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Chemotaxis toward Amino-Acids in Escherichia-Coli
Journal of Bacteriology
Abstract
Escherichia coli cells are shown to be attracted to the l-amino acids alanine, asparagine, aspartate, cysteine, glutamate, glycine, methionine, serine, and threonine, but not to arginine, cystine, glutamine, histidine, isoleucine, leucine, lysine, phenylalanine, tryptophan, tyrosine, or valine. Bacteria grown in a proline-containing medium were, in addition, attracted to proline. Chemotaxis toward amino acids is shown to be mediated by at least two detection systems, the aspartate and serine chemoreceptors. The aspartate chemoreceptor was nonfunctional in the aspartate taxis mutant, which showed virtually no chemotaxis toward aspartate, glutamate, or methionine, and reduced taxis toward alanine, asparagine, cysteine, glycine, and serine. The serine chemoreceptor was nonfunctional in the serine taxis mutant, which was defective in taxis toward alanine, asparagine, cysteine, glycine, and serine, and which showed no chemotaxis toward threonine. Additional data concerning the specificities of the amino acid chemoreceptors with regard to amino acid analogues are also presented. Finally, two essentially nonoxidizable amino acid analogues, alpha-aminoisobutyrate and alpha-methylaspartate, are shown to be attractants for E. coli, demonstrating that extensive metabolism of attractants is not required for amino acid taxis.
... In general, for sugars there is no clear relation between the growth rate afforded by a given sugar and its strength as an attractant 150 . In the figure, we replot data from capillary assay studies performed in the 1970s 150,151 where the chemotactic sensitivities, defined as the negative of the logarithm of the threshold concentration inducing chemotaxis, to many sugars was measured, as well as the growth rate on those sugars when used as a carbon source (red dots). This reveals no clear correlation between measured growth rates and chemotactic sensitivities. ...
... This reveals no clear correlation between measured growth rates and chemotactic sensitivities. Furthermore, the best studied chemotaxis response is that of E. coli to the amino acids aspartate and serine 6,151 . Although E. coli consumes these amino acids first 129 and is attracted more strongly to these than to any sugar 151 (blue lines), these amino acids only sustain low growth yields when provided as the sole carbon source 129 . ...
... Furthermore, the best studied chemotaxis response is that of E. coli to the amino acids aspartate and serine 6,151 . Although E. coli consumes these amino acids first 129 and is attracted more strongly to these than to any sugar 151 (blue lines), these amino acids only sustain low growth yields when provided as the sole carbon source 129 . The chemotaxis preferences of E. coli point to much wider ecological functions of chemotaxis beyond simply tracking the sources of a compound to fuel metabolism. ...
How bacterial chemotaxis is performed is much better understood than why. Traditionally, chemotaxis has been understood as a foraging strategy by which bacteria enhance their uptake of nutrients and energy, yet it has remained puzzling why certain less nutritious compounds are strong chemoattractants and vice versa. Recently, we have gained increased understanding of alternative ecological roles of chemotaxis, such as navigational guidance in colony expansion, localization of hosts or symbiotic partners and contribution to microbial diversity by the generation of spatial segregation in bacterial communities. Although bacterial chemotaxis has been observed in a wide range of environmental settings, insights into the phenomenon are mostly based on laboratory studies of model organisms. In this Review, we highlight how observing individual and collective migratory behaviour of bacteria in different settings informs the quantification of trade-offs, including between chemotaxis and growth. We argue that systematically mapping when and where bacteria are motile, in particular by transgenerational bacterial tracking in dynamic environments and in situ approaches from guts to oceans, will open the door to understanding the rich interplay between metabolism and growth and the contribution of chemotaxis to microbial life.
... 48,49 Nitrogen as a major constituent in all amino acids can be predominantly traced in the bacterial cell. 50 Carbon and oxygen are present in all organic cellular components in the cytoplasm and bacterial cell membrane. 50,51 STEM-EDS elemental mapping of Ni confirmed the presence of nickel element in bacteria upon interacting with unary Ni-Gly particles. ...
... 50 Carbon and oxygen are present in all organic cellular components in the cytoplasm and bacterial cell membrane. 50,51 STEM-EDS elemental mapping of Ni confirmed the presence of nickel element in bacteria upon interacting with unary Ni-Gly particles. Interestingly, the Ni-Gly particles were coated with N, P, and S elements that are representative of bacterial diagnostic elements, suggesting the possible formation of biofilm on the glycerolate particles. ...
While polyelemental alloys are shown to be promising for healthcare applications, their effectiveness in promoting bacterial growth remains unexplored. In the present work, we evaluated the interaction of polyelemental glycerolate particles (PGPs) with Escherichia coli (E. coli) bacteria. PGPs were synthesized using the solvothermal route, and nanoscale random distribution of metal cations in the glycerol matrix of PGPs was confirmed. We observed 7-fold growth of E. coli bacteria upon 4 h of interaction with quinary glycerolate (NiZnMnMgSr-Gly) particles in comparison to control E. coli bacteria. Nanoscale microscopic studies on bacteria interactions with PGPs showed the release of metal cations in the bacterium cytoplasm from PGPs. The electron microscopy imaging and chemical mapping indicated bacterial biofilm formation on PGPs without causing significant cell membrane damage. The data showed that the presence of glycerol in PGPs is effective in controlling the release of metal cations, thus preventing bacterial toxicity. The presence of multiple metal cations is expected to provide synergistic effects of nutrients needed for bacterial growth. The present work provides key microscopic insights of mechanisms by which PGPs enhance biofilm growth. This study opens the door for future applications of PGPs in areas where bacterial growth is essential including healthcare, clean energy, and the food industry.
... 35 Nitrogen is present as a major constituent in all amino acids in the bacterial cell. 36 Carbon is a major component of all organic cellular components in the cytoplasm and bacterial cell membrane. 36 Oxygen is present in proteins, carbohydrates, fatty acids, nucleic acids, and polyphosphates. ...
... 36 Carbon is a major component of all organic cellular components in the cytoplasm and bacterial cell membrane. 36 Oxygen is present in proteins, carbohydrates, fatty acids, nucleic acids, and polyphosphates. 37 Chlorine is responsible for cellular homeostasis and plays an important role in osmotic balance in the bacterial cell. ...
Multi-principal element nanoparticles are an emerging class of materials with potential applications in medicine and biology. However, it is not known how such nanoparticles interact with bacteria at nanoscale. In the present work, we evaluated the interaction of multi-principal elemental alloy (FeNiCu) nanoparticles with Escherichia coli (E. coli) bacteria using the in situ graphene liquid cell (GLC) scanning transmission electron microscopy (STEM) approach. The imaging revealed the details of bacteria wall damage in the vicinity of nanoparticles. The chemical mappings of S, P, O, N, C, and Cl elements confirmed the cytoplasmic leakage of the bacteria. Our results show that there is selective release of metal ions from the nanoparticles. The release of copper ions was much higher than that for nickel while the iron release was the lowest. In addition, the binding affinity of bacterial cell membrane protein functional groups with Cu, Ni, and Fe cations is found to be the driving force behind the selective metal cations' release from the multi-principal element nanoparticles. The protein functional groups driven dissolution of multielement nanoparticles was evaluated using the density functional theory (DFT) computational method, which confirmed that the energy required to remove Cu atoms from the nanoparticle surface was the least in comparison with those for Ni and Fe atoms. The DFT results support the experimental data, indicating that the energy to dissolve metal atoms exposed to oxidation and/or the to presence of oxygen atoms at the surface of the nanoparticle catalyzes metal removal from the multielement nanoparticle. The study shows the potential of compositional design of multi-principal element nanoparticles for the controlled release of metal ions to develop antibacterial strategies. In addition, GLC-STEM is a promising approach for understanding the nanoscale interaction of metallic nanoparticles with biological structures.
... Early studies of chemotaxis showed that bacteria are attracted to common nutrients, such as amino acids or sugars (Adler, Hazelbauer and Dahl 1973;Mesibov and Adler 1972;Pfeffer 1884), while being repelled from harmful conditions such as toxic levels of inorganic ions or extreme pH (Tso and Adler 1974), which led to the assumption that bacteria use chemotaxis to accumulate in environmental niches that provide optimal conditions for growth. Confirming this correlation between chemotactic and metabolic preferences, several studies have shown that, even within the same chemical class, the most potent chemoattractants are those compounds that are also preferentially consumed (Neumann, Grosse and Sourjik 2012;Somavanshi, Ghosh and Sourjik 2016;Yang et al. 2015) or give the shortest lag time in growth when used as a carbon source . ...
... Importantly, these different functions of motility and chemotaxis are not mutually exclusive but contextdependent. Even a single E. coli chemoreceptor Tsr can mediate chemotaxis to the preferentially consumed amino acid serine, to bacterial signaling molecules AI-2 and indole, and to animal hormones (Hegde et al. 2011;Lopes and Sourjik 2018;Mesibov and Adler 1972;Orr et al. 2020;. Consequently, knockouts of individual receptors frequently show pleiotropic defects, from reduced growth fitness under conditions where chemotaxis is important to reduced biofilm formation and virulence. ...
Most swimming bacteria are capable of following gradients of nutrients, signaling molecules and other environmental factors that affect bacterial physiology. This tactic behavior became one of the most-studied model systems for signal transduction and quantitative biology, and underlying molecular mechanisms are well characterized in Escherichia coli and several other model systems. In this review, we focus primarily on less understood aspect of bacterial chemotaxis, namely its physiological relevance for individual bacterial cells and for bacterial populations. As evident from multiple recent studies, even for the same bacterial species flagellar motility and chemotaxis might serve multiple roles, depending on the physiological and environmental conditions. Among these, finding sources of nutrients and more generally locating niches that are optimal for growth appear to be one of the major functions of bacterial chemotaxis, which could explain many chemoeffector preferences as well as flagellar gene regulation. Chemotaxis might also generally enhance efficiency of environmental colonization by motile bacteria, which involves intricate interplay between individual and collective behaviors and trade-offs between growth and motility. Finally, motility and chemotaxis play multiple roles in collective behaviors of bacteria including swarming, biofilm formation and autoaggregation, as well as in their interactions with animal and plant hosts.
... Although Leeuwenhoek already observed the motility of microorganisms in 1670s using his primitive single-lens microscopes, bacterial chemotaxis was not discovered until the late nineteenth century by Engelmann and Pfeffer, who first documented bacterial responses to oxygen [4-6] (for reviews of early chemotaxis research, see [7] and [8]). Subsequent studies have extensively characterized the chemotactic response of bacteria to chemoattractants such as amino acids [9], sugars [10], and dipeptides [11] and chemorepellants such as alcohols [12] and heavy metal cations [13,14]. Despite oxygen's historical significance in the discovery of chemotaxis, it elicits unique and complex behavior in the response of bacteria-referred to as aerotaxis-unobserved with other chemical stimuli. ...
Bacteria navigate their environment by biasing their swimming direction toward beneficial chemicals and away from harmful ones. Out of all the chemicals bacteria respond to, oxygen stands out due to its ubiquitous presence, distinct influence on bacterial metabolism and motility, and historical role in chemotaxis research. However, a coherent understanding of bacterial motility in oxygen gradients, known as aerotaxis , remains elusive, as evidenced by conflicting reports on the migration direction of the model organism Escherichia coli in self-generated oxygen gradients. Here, by combining experiments, simulations, and theory, we provide a unified framework elucidating the fundamental biophysical principle governing bacterial aerotaxis. We track the migration of bacteria in a capillary channel under self-generated oxygen gradients and show that the migration direction depends on the overall bacterial density. At high densities, bacteria migrate toward regions of higher oxygen concentration, whereas at low densities, they move in the opposite direction. We identify a critical bacterial density at which collective migration ceases, despite the presence of oxygen gradients. A kinetic theory, based on the assumption that bacteria seek an optimal oxygen concentration, is then developed to quantitatively explain our experimental findings. We validate this hypothesis by demonstrating the biased movement of individual bacteria in a dense suspension and proposing a signaling pathway that enables this behavior. Thus, by bridging the molecular level understanding of the signaling pathway, the motility of single bacteria in oxygen gradients, and the collective population dynamics shaped by oxygen diffusion and consumption, our study provides a comprehensive understanding of aerotaxis, addressing the long-standing controversy over how bacteria response to non-uniform oxygen distributions pervasive in microbial habitats.
... Amino acids, particularly proteinogenic amino acids, have long been recognized as potent chemoattractants, presumably due to their essential role in biological processes (Mesibov and Adler, 1972;Vuppula et al., 2010). Some of the oldest and most critical biochemical pathways, such as carbon fixation methods, have evolved around the need to synthesize such key amino acids (Braakman and Smith, 2012). ...
One excellent biosignature for the present detection of microbial life on
Earth is motility, leading to its growing interest within the astrobiological
community as an observable attribute that, if detected during future in situ
space missions, could point towards the existence of life on Mars or other
celestial bodies. Microbial motility can be induced by various stimulants,
including certain chemicals called chemoeffectors, leading to subsequent
chemotaxis. Following this concept, this work examines the chemotactic
affinities of the bacteria Bacillus subtilis and Pseudoalteromonas haloplanktis
as well as the archaeon Haloferax volcanii for L-serine, which has been
previously demonstrated to have a high chemoeffective potency across a
wide range of species from all domains of life on Earth. Methodologically,
we introduce here a novel approach for utilizing μ-slides that diverges from
the more traditional long-term chemotactic assay in favor of a shorter time
frame assay that only requires a simple blob detection algorithm for microbial
detection. Given the technical, computational, and time constraints necessary
for an in-situ life detection mission, this simplified approach could be a cost
and resource-effective way to probe for potential chemotactic-responsive
life. Overall, the results indicated that each of the three organisms showed
chemotactic behavior toward L-serine, which, to our knowledge, is the first
time that an L-serine-induced chemotactic response has been detected for
H. volcanii.
... Chemotactic responses were also affected by optical isomerism (i.e., enantiomers). Several bacterial and archaeal strains were attracted towards specific L-amino acids but did not respond to their D-form [41][42][43] , or with a threshold concentration 100 to 1000-fold higher 44 (Table S1). Natural proteins are exclusively built from L-amino acids as D-amino acids cannot be incorporated into proteins via ribosomal synthesis 45 . ...
Chemicals inducing chemotaxis have been characterised for over 60 years across hundreds of publications. Without any synthesis of these scattered results, our current understanding of the molecules affecting prokaryotic behaviours is fragmented. Here, we examined 341 publications to assemble a comprehensive database of prokaryotic chemoeffectors, compiling the effect (attractant, repellent or neutral) of 926 chemicals previously tested and the chemotactic behaviour of 394 strains. Our analysis reveals that (i) not all chemical classes trigger chemotaxis equally, in particular, amino acids and benzenoids are much stronger attractants than carbohydrates; (ii) over one-quarter of attractants tested are not used for growth but solely act as chemotactic signals; (iii) the prokaryote’s origin matters, as terrestrial strains respond to 50% more chemicals than those originating from human or marine biomes; (iv) repellents affect cell behaviour at concentrations 10-fold higher than attractants; (v) the effect of large molecules and the behaviour of bacteria other than Proteobacteria have been largely overlooked. Taken together, our findings provide a unifying view of the chemical characteristics that affect prokaryotic behaviours globally.
... The spray contained two main types of ingredients one active ingredient ciprofloxacin which was coated on nano-particles. The others were inactive ingredients which included PEG-ZnO-NPs, 5% ethanol as solvent to dissolve the nano-formulate, glycerin as a preservative, adhesive agent, for moisturization, as a facilitator in wound healing, and L-aspartic acid as chemoattractant for bacteria 36,37 . For the preparation of nano-therapeutic, the concentration of 10 mg/L NPs was prepared in 5% ethanol solution with proper mixing by stirring for 2 h with random sonication. ...
Antimicrobial resistance is a worldwide health problem that demands alternative antibacterial strategies. Modified nano-composites can be an effective strategy as compared to traditional medicine. The current study was designed to develop a biocompatible nano-drug delivery system with increased efficacy of current therapeutics for biomedical applications. Zinc oxide nanoparticles (ZnO-NPs) were synthesized by chemical and green methods by mediating with Moringa olifera root extract. The ZnO–NPs were further modified by drug conjugation and coating with PEG (CIP-PEG-ZnO-NPs) to enhance their therapeutic potential. PEGylated ZnO-ciprofloxacin nano-conjugates were characterized by Fourier Transform Infrared spectroscopy, X-ray diffractometry, and Scanning Electron Microscopy. During antibacterial screenings chemically and green synthesized CIP-PEG-ZnO-NPs revealed significant activity against clinically isolated Gram-positive and Gram-negative bacterial strains. The sustainable and prolonged release of antibiotics was noted from the CIP–PEG conjugated ZnO-NPs. The synthesized nanoparticles were found compatible with RBCs and Baby hamster kidney cell lines (BHK21) during hemolytic and MTT assays respectively. Based on initial findings a broad-spectrum nano-material was developed and tested for biomedical applications that eradicated Staphylococcus aureus from the infectious site and showed wound-healing effects during in vivo applications. ZnO-based nano-drug carrier can offer targeted drug delivery, and improved drug stability and efficacy resulting in better drug penetration.
... A chemoreceptor can sense ligands other than its cognate attractant; e.g., Tar can bind serine albeit with a much lower affinity [48,49]. Though we incorporate the term of Tar-serine sensing, f 3 , in all our model simulations and analysis, we claim that it does not change the qualitative conclusions. ...
Although bacterial chemotaxis behavior in a single gradient has been well studied, chemotaxis of bacterial population in complex environments is not well understood. Here, we discovered four distinct behaviors of populations in microfluidic experiments with different opposing gradients of MeAsp and serine. By using a population chemotaxis model based on the dynamics of intracellular signaling pathways, we found that the nongenetic variability of the relevant chemoreceptors (Tar and Tsr) within the population is responsible for the diverse population behaviors. Through analyses combining the phenotype-to-performance mapping and Tar/Tsr ratio distribution, we predicted the phase diagram of population chemotaxis behaviors under varying chemical gradients and the effect of growth period on population behaviors, which were verified by additional experiments. Our study suggests that phenotypic heterogeneity in chemoreceptors enables diverse chemotactic strategies, which cells may adopt to improve their population fitness in complex environments.
Published by the American Physical Society 2024
... We measured the response of individual cells to a decrease in concentration of α-methyl-DL-aspartate (MeAsp), a non-metabolizable analog of L-aspartate 52 that acts as a chemoattractant 52,53 . We used a three-channel flow chamber (Fig. 4a) to observe the effect of a step-down from 1 to 0 mM MeAsp on individual optically trapped wild-type cells. ...
The Escherichia coli chemotaxis network, by which bacteria modulate their random run/tumble swimming pattern to navigate their environment, must cope with unavoidable number fluctuations (“noise”) in its molecular constituents like other signaling networks. The probability of clockwise (CW) flagellar rotation, or CW bias, is a measure of the chemotaxis network’s output, and its temporal fluctuations provide a proxy for network noise. Here we quantify fluctuations in the chemotaxis signaling network from the switching statistics of flagella, observed using time-resolved fluorescence microscopy of individual optically trapped E. coli cells. This approach allows noise to be quantified across the dynamic range of the network. Large CW bias fluctuations are revealed at steady state, which may play a critical role in driving flagellar switching and cell tumbling. When the network is stimulated chemically to higher activity, fluctuations dramatically decrease. A stochastic theoretical model, inspired by work on gene expression noise, points to CheY activation occurring in bursts, driving CW bias fluctuations. This model also shows that an intrinsic kinetic ceiling on network activity places an upper limit on activated CheY and CW bias, which when encountered suppresses network fluctuations. This limit may also prevent cells from tumbling unproductively in steep gradients.
... While the core of the signaling pathway is conserved among bacteria, the number and specificity of chemoreceptors are highly variable and strain specific (6). The reported repertoire of signals recognized by chemoreceptors across bacterial species includes not only proteinogenic amino acids (7,8), polyamines (9), quaternary amines (10), nucleoba ses and their derivatives (11,12), organic acids (13,14), and sugars (15) but also inorganic ions (16,17), pH (18)(19)(20), and temperature (21,22). Nevertheless, the signal specificity remains unknown for the absolute majority of chemoreceptors. ...
The chemotaxis network, one of the most prominent prokaryotic sensory systems, is present in most motile bacteria and archaea. Although the conserved signaling core of this network is well characterized, ligand specificities of a large majority of diverse chemoreceptors encoded in bacterial genomes remain unknown. Here, we performed a systematic identification and characterization of new chemoeffectors for the opportunistic pathogen Pseudomonas aeruginosa, which has 26 chemoreceptors possessing most of the common types of ligand binding domains. By performing capillary chemotaxis assays for a library of growth-promoting compounds, we first identified a number of novel chemoattractants of varying strength. We subsequently mapped specificities of these ligands by performing Förster resonance energy transfer and microfluidic measurements for 16 hybrid chemoreceptors that combine the periplasmic ligand binding domains of P. aeruginosa receptors and the cytoplasmic signaling domain of the Escherichia coli Tar receptor. Direct binding of putative ligands to chemoreceptors was further confirmed using thermal shift assay and microcalorimetry. Altogether, the combination of methods enabled us to assign several new attractants, including methyl 4-aminobutyrate, 5-aminovalerate, L-ornithine, 2-phenylethylamine, and tyramine, to previously characterized chemoreceptors and to annotate a novel purine-specific receptor PctP. Responses of hybrid receptors to changes in pH further revealed a complex bidirectional pH sensing mechanism in P. aeruginosa, which involves at least four chemoreceptors PctA, PctC, TlpQ, and PctP. Our screening strategy could be applied for the systematic characterization of unknown sensory domains in a wide range of bacterial species.
IMPORTANCE
Chemotaxis of motile bacteria has multiple physiological functions. It enables bacteria to locate optimal ecological niches, mediates collective behaviors, and can play an important role in infection. These multiple functions largely depend on ligand specificities of chemoreceptors, and the number and identities of chemoreceptors show high diversity between organisms. Similar diversity is observed for the spectra of chemoeffectors, which include not only chemicals of high metabolic value but also bacterial, plant, and animal signaling molecules. However, the systematic identification of chemoeffectors and their mapping to specific chemoreceptors remains a challenge. Here, we combined several in vivo and in vitro approaches to establish a systematic screening strategy for the identification of receptor ligands and we applied it to identify a number of new physiologically relevant chemoeffectors for the important opportunistic human pathogen P. aeruginosa. This strategy can be equally applicable to map specificities of sensory domains from a wide variety of receptor types and bacteria.
... Chemotaxis towards d-Arg may have a nutritional purpose. This idea is supported by results in E. coli showing that certain compounds with low nutritional value can be chemoattractants 44 and by the presence of a catabolic d-amino acid dehydrogenase enzyme 45 . The crystal structures of the LBD of MCP DRK showed that it has a typical antiparallel 4HB structure, which is conserved in various receptors 46 . ...
To explore favourable niches while avoiding threats, many bacteria use a chemotaxis navigation system. Despite decades of studies on chemotaxis, most signals and sensory proteins are still unknown. Many bacterial species release d-amino acids to the environment; however, their function remains largely unrecognized. Here we reveal that d-arginine and d-lysine are chemotactic repellent signals for the cholera pathogen Vibrio cholerae. These d-amino acids are sensed by a single chemoreceptor MCPDRK co-transcribed with the racemase enzyme that synthesizes them under the control of the stress-response sigma factor RpoS. Structural characterization of this chemoreceptor bound to either d-arginine or d-lysine allowed us to pinpoint the residues defining its specificity. Interestingly, the specificity for these d-amino acids appears to be restricted to those MCPDRK orthologues transcriptionally linked to the racemase. Our results suggest that d-amino acids can shape the biodiversity and structure of complex microbial communities under adverse conditions.
... One plausible mechanism for a cell density-dependent consumption rate of Asp is spatial variations in the concentration of dissolved oxygen, which is required by E. coli to consume Asp (17,53). Oxygen is consumed by E. coli (6,17), but it can be replenished by permeation through the PDMS chip (54). ...
Chemotactic bacteria not only navigate chemical gradients, but also shape their environments by consuming and secreting attractants. Investigating how these processes influence the dynamics of bacterial populations has been challenging because of a lack of experimental methods for measuring spatial profiles of chemoattractants in real time. Here, we use a fluorescent sensor for aspartate to directly measure bacterially generated chemoattractant gradients during collective migration. Our measurements show that the standard Patlak-Keller-Segel model for collective chemotactic bacterial migration breaks down at high cell densities. To address this, we propose modifications to the model that consider the impact of cell density on bacterial chemotaxis and attractant consumption. With these changes, the model explains our experimental data across all cell densities, offering new insight into chemotactic dynamics. Our findings highlight the significance of considering cell density effects on bacterial behavior, and the potential for fluorescent metabolite sensors to shed light on the complex emergent dynamics of bacterial communities.
SIGNIFICANCE STATEMENT
During collective cellular processes, cells often dynamically shape and respond to their chemical environments. Our understanding of these processes is limited by the ability to measure these chemical profiles in real time. For example, the Patlak-Keller-Segel model has widely been used to describe collective chemotaxis towards self-generated gradients in various systems, albeit without direct verification. Here we used a biocompatible fluorescent protein sensor to directly observe attractant gradients created and chased by collectively-migrating bacteria. Doing so uncovered limitations of the standard chemotaxis model at high cell densities and allowed us to establish an improved model. Our work demonstrates the potential for fluorescent protein sensors to measure the spatiotemporal dynamics of chemical environments in cellular communities.
... On smaller scales, directed motion of colloidal particles can be achieved through different mechanisms including thermophoresis (6), diffusiophoresis (7,8), photocatalysis (9,10), induced-charge electrophoresis (11), and Quincke rotation (12)(13)(14). On the other hand, the biological world exploits self-propulsion to, inter alia, explore surroundings for nutrition (15,16) and migrate to more conducive environments (17). A rapidly growing body of studies has demonstrated that physical interactions (both steric and hydrodynamic) are sufficient for the emergence of a wealth of collective dynamic states such as clustering (7,9) and swarming (18) in microscopic active systems (19). ...
Emergent behavior in collectives of "robotic" units with limited capabilities that is robust and programmable is a promising route to perform tasks on the micro and nanoscale that are otherwise difficult to realize. However, a comprehensive theoretical understanding of the physical principles, in particular steric interactions in crowded environments, is still largely missing. Here, we study simple light-driven walkers propelled through internal vibrations. We demonstrate that their dynamics is well captured by the model of active Brownian particles, albeit with an angular speed that differs between individual units. Transferring to a numerical model, we show that this polydispersity of angular speeds gives rise to specific collective behavior: self-sorting under confinement and enhancement of translational diffusion. Our results show that, while naively perceived as imperfection, disorder of individual properties can provide another route to realize programmable active matter.
... 36 Similarly, Escherichia coli relies on numerous amino acids for microbial protein synthesis. 37 When in vitro models were used during spaceflight, a potent increase in E. coli growth occurred compared with ground-based models. 30,34 However, human models have not examined the effects of spaceflight on E. coli composition. ...
Spaceflight exerts an extreme and unique influence on human physiology as astronauts are subjected to long-term or short-term exposure to microgravity. During spaceflight, a multitude of physiological changes, including the loss of skeletal muscle mass, bone resorption, oxidative stress, and impaired blood flow, occur, which can affect astronaut health and the likelihood of mission success. In vivo and in vitro metabolite studies suggest that amino acids are among the most affected nutrients and metabolites by microgravity (a weightless condition due to very weak gravitational forces). Moreover, exposure to microgravity alters gut microbial composition, immune function, musculoskeletal health, and consequently amino acid metabolism. Appropriate knowledge of daily protein consumption, with a focus on specific functional amino acids, may offer insight into potential combative and/or therapeutic effects of amino acid consumption in astronauts and space travelers. This will further aid in the successful development of long-term manned space mission and permanent space habitats.
... The metR gene encodes the transcriptional activator of metE (34). Methionine was described by Julius Adler as one of the amino acids toward which E. coli can perform chemotaxis through the aspartate receptor Tar (35). From methionine, the enzyme S-adenosylmethionine (SAM) synthetase (encoded by metK) leads to the production of SAM (36), which serves as donor of the methyl group for the methylation of the chemoreceptors and methylaccepting chemotaxis proteins (MCPs) by CheR (37,38). ...
This study investigates migration phenotypes of 265 Escherichia coli soil isolates from the Buffalo River basin in Minnesota, USA. Migration rates on semisolid tryptone swim plates ranged from nonmotile to 190% of the migration rate of a highly motile E. coli K-12 strain. The nonmotile isolate, LGE0550, had mutations in flagellar and chemotaxis genes, including two IS3 elements in the flagellin-encoding gene fliC. A genome-wide association study (GWAS), associating the migration rates with genetic variants in specific genes, yielded two metabolic variants (rygD-serA and metR-metE) with previous implications in chemotaxis. As a novel way of confirming GWAS results, we used minimal medium swim plates to confirm the associations. Other variants in metabolic genes and genes that are associated with biofilm were positively or negatively associated with migration rates. A determination of growth phenotypes on Biolog EcoPlates yielded differential growth for the 10 tested isolates on d-malic acid, putrescine, and d-xylose, all of which are important in the soil environment.
IMPORTANCE E. coli is a Gram-negative, facultative anaerobic bacterium whose life cycle includes extra host environments in addition to human, animal, and plant hosts. The bacterium has the genomic capability of being motile. In this context, the significance of this study is severalfold: (i) the great diversity of migration phenotypes that we observed within our isolate collection supports previous (G. NandaKafle, A. A. Christie, S. Vilain, and V. S. Brözel, Front Microbiol 9:762, 2018, https://doi.org/10.3389/fmicb.2018.00762; Y. Somorin, F. Abram, F. Brennan, and C. O’Byrne, Appl Environ Microbiol 82:4628–4640, 2016, https://doi.org/10.1128/AEM.01175-16) ideas of soil promoting phenotypic heterogeneity, (ii) such heterogeneity may facilitate bacterial growth in the many different soil niches, and (iii) such heterogeneity may enable the bacteria to interact with human, animal, and plant hosts.
... One of the key ways that bacteria physiologically respond to chemicals in their environment is via chemotaxis; the ability of cells to bias their motility in response to chemical gradients 15,16 . There is a large literature on swimming (flagella-driven) chemotaxis, which broadly suggests that cells have the ability to move towards beneficial conditions and away from harmful ones [17][18][19][20][21][22] . However, to our knowledge, there is no evidence that swimming cells bias their movement in response to antibiotics. ...
Bacteria commonly live in surface-associated communities where steep gradients of antibiotics and other chemical compounds can occur. While many bacterial species move on surfaces, we know surprisingly little about how such antibiotic gradients affect cell motility. Here, we study the behaviour of the opportunistic pathogen Pseudomonas aeruginosa in stable spatial gradients of several antibiotics by tracking thousands of cells in microfluidic devices as they form biofilms. Unexpectedly, these experiments reveal that bacteria use pili-based (‘twitching’) motility to navigate towards antibiotics. Our analyses suggest that this behaviour is driven by a general response to the effects of antibiotics on cells. Migrating bacteria reach antibiotic concentrations hundreds of times higher than their minimum inhibitory concentration within hours and remain highly motile. However, isolating cells - using fluid-walled microfluidic devices - reveals that these bacteria are terminal and unable to reproduce. Despite moving towards their death, migrating cells are capable of entering a suicidal program to release bacteriocins that kill other bacteria. This behaviour suggests that the cells are responding to antibiotics as if they come from a competing colony growing nearby, inducing them to invade and attack. As a result, clinical antibiotics have the potential to lure bacteria to their death.
... For typical soft interfaces, the bending modulus κ β ≈ 10 −19 J [55,57], so if one considers a viscosity approximately that of water, η 1 ≈ 10 −3 N s/m 2 , and swimmers of length L ≈ 10 μm (cell body + flagellar bundle combined), then t c1 ≈ 10 s. In general, microscopic swimmers also respond to external cues, such as an externally imposed flow [26][27][28]31,34,37,72,82] or some form of chemical actuation [83][84][85][86][87][88][89][90], that can influence their migration on such long timescales. Typically, even in the absence of such an external driving force, the reorientations take seconds, as most microscopic swimmers have an inherent mechanism allowing them to change their orientation [49,71,72,91]. ...
We study the coupled hydrodynamics between a motile slender microswimmer and a deformable interface that separates two Newtonian fluid regions. From the disturbance field generated by the swimming motion, we quantitatively characterize the interface deformation and the manner in which the coupling modifies the microswimmer translation itself. We treat the role of the swimmer type (pushers and pullers), size and model an interface that can deform due to both surface tension and bending elasticity. Our analysis reveals a strong dependence of the hydrodynamics on the swimmer orientation and position. Given the viscosities of the two fluid media, the interface properties and the swimmer type, a swimmer can either migrate toward or away from the interface depending on its configurations. When the swimmer is oriented parallel to the interface, a pusher-type swimmer is repelled from the interface at short times if it is swimming in the more viscous fluid. At long times, however, pushers are always attracted to the interface, and pullers are always repelled from it. However, swimmers oriented orthogonal to the interface exhibit a migration pattern opposite to the parallel swimmers. In consequence, a host of complex migration trajectories emerge for swimmers arbitrarily oriented to the interface. We find that confining a swimmer between a rigid boundary and a deformable interface results in regimes of attraction toward both surfaces depending on the swimmer location in the channel, irrespective viscosity ratio. The differing migration patterns are most prominent in a region of order the swimmer size from the interface, where the slender swimmer model yields a better approximation to the coupled hydrodynamics.
... For 6 h experiments, a chemotactic mechanism is thought to be responsible for increased attachment. Indeed, 50 years ago Escherichia coli was found to display chemotactic behaviour towards amino acids (Mesibov and Adler 1972). Although chemotaxis in some bacterial species has been established in relation to amino acids, the link between amino acids as conditioning film molecules and attachment has so far not been evaluated to the best of the authors' knowledge. ...
Microbiologically influenced corrosion and biofouling of steels depend on the adsorption of a conditioning film and subsequent attachment of bacteria. Extracellular deoxyribonucleic acid (eDNA) and amino acids are biologically critical nutrient sources and are ubiquitous in marine environments. However, little is known about their role as conditioning film molecules in early biofilm formation on metallic surfaces. The present study evaluated the capacity for eDNA and amino acids to form a conditioning film on carbon steel (CS), and subsequently, the influence of these conditioning films on bacterial attachment using a marine bacterial strain. Conditioning films of eDNA or amino acids were formed on CS through physical adsorption. Biochemical and microscopic analysis of eDNA conditioning, amino acid conditioning and control CS surfaces demonstrated that organic conditioning surfaces promoted bacterial attachment. The results highlight the importance of conditioning the surface in initial bacterial attachment to steel.
... The media used in our experiments have L -serine as the most abundant nutrient source and chemoattractant (Neidhardt et al., 1974). E. coli consume this amino acid first (Yang et al., 2015) and respond to it most strongly as a chemoattractant compared to other components of the media (Wong et al., 2014;Mesibov and Adler, 1972;Adler, 1966;Menolascina et al., 2017). Furthermore, the nutrient levels of our liquid medium are nearly two orders of magnitude larger than the levels under which E. coli excrete appreciable amounts of their own chemoattractant (Budrene and Berg, 1991) and generate strikingly different front behavior (Budrene and Berg, 1991;Budrene and Berg, 1995;Mittal et al., 2003) than those that arise in our experiments; however, the nutrient levels we use are sufficiently low to avoid toxicity associated with extremely large levels of L -serine (Neumann et al., 2014). ...
ELife digest
Flocks of birds, schools of fish and herds of animals are all good examples of collective migration, where individuals co-ordinate their behavior to improve survival. This process also happens on a cellular level; for example, when bacteria consume a nutrient in their surroundings, they will collectively move to an area with a higher concentration of food via a process known as chemotaxis.
Several studies have examined how disturbing collective migration can cause populations to fall apart. However, little is known about how groups withstand these interferences. To investigate, Bhattacharjee, Amchin, Alert et al. studied bacteria called Escherichia coli as they moved through a gel towards nutrients.
The E. coli were injected into the gel using a three-dimensional printer, which deposited the bacteria into a wiggly shape that forces the cells apart, making it harder for them to move as a collective group. However, as the bacteria migrated through the gel, they smoothed out the line and gradually made it straighter so they could continue to travel together over longer distances.
Computer simulations revealed that this smoothing process is achieved by differences in how the cells respond to local nutrient levels based on their position. Bacteria towards the front of the group are exposed to more nutrients, causing them to become oversaturated and respond less effectively to the nutrient gradient. As a result, they move more slowly, allowing the cells behind them to eventually catch-up.
These findings reveal a general mechanism in which limitations in how individuals sense and respond to an external signal (in this case local nutrient concentrations) allows them to continue migrating together. This mechanism may apply to other systems that migrate via chemotaxis, as well as groups whose movement is directed by different external factors, such as temperature and light intensity.
... Some advantages are the inability for metabolization, conserving a strong chemotactic response and maintaining the study concentration. The analogues helped to demonstrate that chemoattraction to the substances can be independent of the metabolic benefit of transport or can metabolize them [36]. We consider that the aspartate analogues interact with the dedicated MCP receptor and in this way a signal is sent in such a manner that it activates metabolism. ...
Biotin is a key cofactor of metabolic carboxylases, although many rhizobial strains are biotin auxotrophs. When some of these strains were serially subcultured in minimal medium, they showed diminished growth and increased excretion of metabolites. The addition of biotin, or genetic complementation with biotin synthesis genes resulted in full growth of Rhizobium etli CFN42 and Rhizobium phaseoli CIAT652 strains. Half of rhizobial genomes did not show genes for biotin biosynthesis, but three-quarters had genes for biotin transport. Some strains had genes for an avidin homologue (rhizavidin), a protein with high affinity for biotin but an unknown role in bacteria. A CFN42-derived rhizavidin mutant showed a sharper growth decrease in subcultures, revealing a role in biotin storage. In the search of biotin-independent growth of subcultures, CFN42 and CIAT652 strains with excess aeration showed optimal growth, as they also did, unexpectedly, with the addition of aspartic acid analogues α- and N -methyl aspartate. Aspartate analogues can be sensed by the chemotaxis aspartate receptor Tar. A tar homologue was identified and its mutants showed no growth recovery with aspartate analogues, indicating requirement of the Tar receptor in such a phenotype. Additionally, tar mutants did not recover full growth with excess aeration. A Rubisco-like protein was found to be necessary for growth as the corresponding mutants showed no recovery either with high aeration or aspartate analogues; also, diminished carboxylation was observed. Taken together, our results indicate a route of biotin-independent growth in rhizobial strains that included oxygen, a Tar receptor and a previously uncharacterized Rubisco-like protein.
... One of the key ways that bacteria physiologically respond to chemicals in their environment is via chemotaxis; the ability of cells to bias their motility in response to chemical gradients (15,16). There is a large literature on swimming (flagella-driven) chemotaxis, which broadly suggests that cells have the ability to move towards beneficial conditions and away from harmful ones (17)(18)(19)(20)(21)(22). However, to our knowledge, there is no evidence that swimming cells bias their movement in response to antibiotics. ...
Bacteria commonly live in communities on surfaces where steep gradients of antibiotics and other chemical compounds routinely occur. While many species of bacteria can move on surfaces, we know surprisingly little about how such antibiotic gradients affect cell motility. Here we study the behaviour of the opportunistic pathogen Pseudomonas aeruginosa in stable spatial gradients of a range of antibiotics by tracking thousands of cells in microfluidic devices as they form biofilms. Unexpectedly, these experiments reveal that individual bacteria use pili-based ('twitching') motility to actively navigate towards regions with higher antibiotic concentrations. Our analyses suggest that this biased migration is driven, at least in part, by a direct response to the antibiotics. Migrating cells can reach antibiotic concentrations hundreds of times higher than their minimum inhibitory concentration in a few hours and remain highly motile. However, isolating these cells - using fluid-walled microfluidic devices that can be reconfigured in situ - suggests that these bacteria are terminal and not able to reproduce. In spite of moving towards their death, we show that migrating cells are capable of entering a suicidal program to release bacteriocins that are used to kill other bacteria. Our work suggests that bacteria respond to antibiotics as if they come from a competing colony growing in the neighbourhood, inducing them to invade and attack. As a result, clinical antibiotics have the potential to serve as a bait that lures bacteria to their death.
... For typical soft interfaces, the bending modulus κ β ≈ 10 −19 J [55,57], so if one considers a viscosity approximately that of water, η 1 ≈ 10 −3 , and swimmers of length L ≈ 10µm (cell body+flagellar bundle combined), then t c1 ≈ 10s. In general, microscopic swimmers also respond to external cues, such as an externally imposed flow [26,27,28,31,34,37,67,73] or some form of chemical actuation [74,75,76,77,78,79,80,81], that can influence their migration on such long time scales. Typically, even in the absence of such an external driving force, the reorientations take seconds, as most microscopic swimmers have an inherent mechanism allowing them to change their orientation [49,66,67,82]. ...
We study the coupled hydrodynamics between a motile slender microswimmer and a deformable interface that separates two Newtonian fluid regions. From the disturbance field generated by the swimming motion, we quantitatively characterize the interface deformation and the manner in which the coupling modifies the microswimmer translation itself. We treat the role of the swimmer type (pushers and pullers), size and model an interface that can deform due to both surface tension and bending elasticity. Our analysis reveals a strong dependence of the hydrodynamics on the swimmer orientation and position. Given the viscosities of the two fluid media, the interface properties and the swimmer type, a swimmer can either migrate towards or away from the interface depending on its configurations. When the swimmer is oriented parallel to the interface, a pusher-type swimmer is repelled from the interface at short times if it is swimming in the more viscous fluid. At long times however, pushers are always attracted to the interface, and pullers are always repelled from it. In contrast, when the swimmers are oriented orthogonal to the interface, there is a decoupling of the hydrodynamics, resulting in a swimmer translation that is stationary in time. In this case, a pusher-type swimmer is always repelled from the interface when it occupies the low viscosity fluid, and attracted otherwise. The differing migration patterns are most prominent in a region of order the swimmer size from the interface, where the slender swimmer model yields a better approximation to the coupled hydrodynamics.
... The growing evidence indicates that Glu might control bacterial behaviors, including chemotaxis (Brown and Berg, 1974;Craven and Montie, 1985;Mesibov and Adler, 1972;Ordal and Gibson, 1977;Yang et al., 2015), to its theoretical limits (Brumley et al., 2019) as well as social-type communications within biofilms Martinez-Corral et al., 2018). The stress responses in bacteria also recruit γ-aminobutyrate (GABA) as a part of systemic adaptations with a prominent Glu/GABA coupled transporter. ...
Glutamate (Glu) is the primary excitatory transmitter in the mammalian brain. But, we know little about the evolutionary history of this adaptation, including the selection of l-glutamate as a signaling molecule in the first place. Here, we used comparative metabolomics and genomic data to reconstruct the genealogy of glutamatergic signaling. The origin of Glu-mediated communications might be traced to primordial nitrogen and carbon metabolic pathways. The versatile chemistry of L-Glu placed this molecule at the crossroad of cellular biochemistry as one of the most abundant metabolites. From there, innovations multiplied. Many stress factors or injuries could increase extracellular glutamate concentration, which led to the development of modular molecular systems for its rapid sensing in bacteria and archaea. More than 20 evolutionarily distinct families of ionotropic glutamate receptors (iGluRs) have been identified in eukaryotes. The domain compositions of iGluRs correlate with the origins of multicellularity in eukaryotes. Although L-Glu was recruited as a neuro-muscular transmitter in the early-branching metazoans, it was predominantly a non-neuronal messenger, with a possibility that glutamatergic synapses evolved more than once. Furthermore, the molecular secretory complexity of glutamatergic synapses in invertebrates (e.g., Aplysia) can exceed their vertebrate counterparts. Comparative genomics also revealed 15+ subfamilies of iGluRs across Metazoa. However, most of this ancestral diversity had been lost in the vertebrate lineage, preserving AMPA, Kainate, Delta, and NMDA receptors. The widespread expansion of glutamate synapses in the cortical areas might be associated with the enhanced metabolic demands of the complex brain and compartmentalization of Glu signaling within modular neuronal ensembles.
... E. coli is able to recognize rather minute differences between the isomeric forms of hexose sugar molecules and the equally subtle differences between aminoacid and non-aminoacid forms of simple organic molecules (Macnab, 1979/315-316). Bacterium reacts to the 100 times more dilute solution of aspartate molecules than to its methylated form (Mesibov and Adler, 1972). It reacts to 1000 times more dilute solution of galactose than to its analog, 2-deoxy-D-galactose (Adler et al, 1973). ...
Since more than hundred years the attempts to explain biological adaptations constitute the main current of evolutionary thinking. In 1901 C. LI. Morgan wrote: „The doctrine of evolution has rendered the study of adaptation of scientific importance. Before that doctrine was formulated, natural adaptations formed part of the mystery of special creation, and played a great role in natural theology through the use of the argument from 'design in nature’". The modem doctrine of biology stresses the importance of the environment in „shaping" the inner properties of every living being. This means an obvious although tacit refusal to assume or recognize any single, integrated agent in the origin of main functional biological traits and in the genesis of new kinds of life. The role ascribed to random mutations, and to „pressures of the environment" is just one aspect of the neodarwinian theory. Another aspect of this doctrine is the widespread conviction that all phenomena of life are a natural, both random and necessary result of interactions between constantly changing material objects.
... This method consists of introducing a capillary with chemoattractant into a bacterial solution that is subsequently deposited on an agar plate, and after its incubation, the number of colonies is quantified. By means of this methodology, Mesibov and Adler (1972) demonstrated that E. coli was attracted to several amino acids, including L-aspartate, showing a peak at a concentration of 10 mM. Wolfe and Berg used the strategy of incorporating L-aspartate into agar plates and determined that E. coli shows maximum attraction at 10 µM (Wolfe and Berg, 1989). ...
Some bacteria have coevolved to establish symbiotic or pathogenic relationships with plants, animals or humans. With human association, the bacteria can cause a variety of diseases. Thus, understanding bacterial phenotypes at the single‐cell level is essential to develop beneficial applications. Traditional microbiological techniques have provided great knowledge about these organisms; however, they have also shown limitations, such as difficulties in culturing some bacteria, the heterogeneity of bacterial populations or difficulties in recreating some physical or biological conditions. Microfluidics is an emerging technique that complements current biological assays. Since microfluidics works with micrometric volumes, it allows fine‐tuning control of the test conditions. Moreover, it allows the recruitment of three‐dimensional (3D) conditions, in which several processes can be integrated and gradients can be generated, thus imitating physiological 3D environments. Here, we review some key microfluidic‐based studies describing the effects of different microenvironmental conditions on bacterial response, biofilm formation and antimicrobial resistance. For this aim, we present different studies classified into six groups according to the design of the microfluidic device: (i) linear channels, (ii) mixing channels, (iii) multiple floors, (iv) porous devices, (v) topographic devices and (vi) droplet microfluidics. Hence, we highlight the potential and possibilities of using microfluidic‐based technology to study bacterial phenotypes in comparison with traditional methodologies.
... We steer the pipette tip to the target and rely on diffusion for the delivery and release of the payload. This technique is common in microbiology for chemotaxis assays [95] and replicates intercellular delivery systems, which often rely on close proximity and diffusion between cells. The pipette aperture, molecular concentration as well as dwell time can be chosen to control the transfer of molecular species. ...
Autonomous fleets of small-scale robots have the potential to enhance operations or open entirely new avenues in domains ranging from medicine to manufacturing. For instance, microrobots could serve as vehicles to deliver therapeutics, assistants to manipulate cells in microbiological experiments, or agents to assemble microscale objects. In order to realize these applications, microrobots must locomote precisely, gather information from their environment, communicate to share information, and use that information to make decisions. Developing the key actuation, sensing, control, information processing, and associated fabrication methods, which underpin these high-level tasks, is still a significant challenge. In this dissertation, we present biohybrid approaches to microrobot design and fabrication in which organic and synthetic materials are synergistically combined to create a new class of microscale robotic systems, which we call "robotic wetware." By interfacing synthetic hardware and software with programmable living cells, we develop components and subsystems to enable more functional microrobots. We begin by designing and demonstrating biological actuation methods with an approach to simultaneously power and control groups of microstructures using active bacterial baths. We then introduce soft micro bio robots (SMBRs), the first microrobot platform which integrates on-board components derived from synthetic biology. We formulate a biocompatible fabrication method based on 3D printing and molding. We design SMBRs to harbor a suite of low-level functions including actuation and sensing, as well as sophisticated capabilities such as chemical or cellular delivery and biofilm remediation. We actuate SMBRs using applied magnetic fields, and use genetic engineering to design and construct living sensors, chemical actuators, and information processors which function on-board as additional elements of the feedback control loop. Similarly, we demonstrate microrobots as components of feedback control loops in biological circuits and show that robots carrying chemical actuators and biosensors can interrogate synthetic biological systems at a range of spatiotemporal scales. Finally, we develop strategies for multi-microrobot control and demonstrate teams of diamagnetically levitated milliscale robots equipped with manipulators such that they function as mobile assistants in microbiological experiments. These contributions constitute a suite of strategies for small-scale actuation, control, sensing, and information processing, and together form the enabling subsystems for autonomous biocompatible swarms.
... The media used in our experiments have L-serine as the most abundant nutrient source and chemoattractant 69 . E. coli consume this amino acid first 49 and respond to it most strongly as a chemoattractant compared to other components of the media 6,36,70,71 . Furthermore, the nutrient levels of our liquid medium are nearly two orders of magnitude larger than the levels under which E. coli excrete appreciable amounts of their own chemoattractant 72 and generate strikingly different front behavior 72-74 than those that arise in our experiments; however, the nutrient levels we use are sufficiently low to avoid toxicity associated with extremely large levels of L-serine 75 . ...
Collective migration -- the directed, coordinated motion of many self-propelled agents -- is a fascinating emergent behavior exhibited by active matter that has key functional implications for biological systems. Extensive studies have elucidated the different ways in which this phenomenon may arise. Nevertheless, how collective migration can persist when a population is confronted with perturbations, which inevitably arise in complex settings, is poorly understood. Here, by combining experiments and simulations, we describe a mechanism by which collectively migrating populations smooth out large-scale perturbations in their overall morphology, enabling their constituents to continue to migrate together. We focus on the canonical example of chemotactic migration of Escherichia coli, in which fronts of cells move via directed motion, or chemotaxis, in response to a self-generated nutrient gradient. We identify two distinct modes in which chemotaxis influences the morphology of the population: cells in different locations along a front migrate at different velocities due to spatial variations in (i) the local nutrient gradient and in (ii) the ability of cells to sense and respond to the local nutrient gradient. While the first mode is destabilizing, the second mode is stabilizing and dominates, ultimately driving smoothing of the overall population and enabling continued collective migration. This process is autonomous, arising without any external intervention; instead, it is a population-scale consequence of the manner in which individual cells transduce external signals. Our findings thus provide insights to predict, and potentially control, the collective migration and morphology of cell populations and diverse other forms of active matter.
Nucleosides are essential components of all living cells. Bacteria use salvage pathways to import nucleosides from their environment and to utilize them for nucleic acid biosynthesis, but also as alternative sources of carbon, nitrogen and energy. Motile bacteria commonly show chemoattraction towards nutritionally valuable compounds, and in this work, we demonstrate that the chemotaxis pathway of Escherichia coli exhibits specific attractant response to pyrimidine nucleosides. Particularly sensitive response, in the sub-micromolar range, was observed for deoxyribonucleosides thymidine and deoxycytidine. In contrast, ribonucleosides elicited weaker and less sensitive response, and no response to pyrimidine nucleobases was observed in the micromolar range of concentrations. Our subsequent analysis revealed that the pathway response to pyrimidine deoxyribonucleosides is mediated by the minor E. coli chemoreceptor Tap. The observed narrow dynamic range of this response indicates that sensing of deoxyribonucleosides is indirect, likely via an unknown periplasmic binding protein that interacts with Tap.
The focus of this report is to assess the role that amino acids, together with insulin, play in adherence to plastic and latex under various temperatures and bacterial growth stages. Various gram-negative bacteria were grown in minimal medium to either logarithmic (log) or stationary (stat) growth phase. The adherence of washed cells to plastic or latex was determined using multiwell plates or 6-mm latex squares at 22°C or 37°C in a buffer containing physiological insulin levels (20 or 200 μU/ml), with and without the amino acids tested (10−1 to 10−3 M). The controls were buffer alone, insulin alone, and amino acid alone. Only seven of the 20 amino acids tested modulated adherence to plastic and/or latex. No global pattern based on the amino acid structure was evident. Insulin did not affect adherence in the presence of alanine, valine, aspartic acid, glutamine, and lysine. Arginine (Arg; 10−1 to 10−2 M) inhibited adherence to latex (but not plastic) and dispersed preformed biofilms for all organisms except Acinetobacter baumannii. At a biofilm-permissive Arg concentration (10−3 M), insulin (200 µU) restored the inhibitory effect of Arg. These findings may provide insights into material composition modifications that could have clinical and industrial applications.
A 3D microfluidic platform for single-cell chemotaxis studies and active cell sorting based on chemotactic phenotypes across diverse applications.
The bacterial chemotaxis system is one of the best-understood cellular pathways and serves as the model for signal transduction systems. Most chemotaxis research has been conducted with transmembrane chemotaxis systems from Escherichia coli and has established paradigms of the system that were thought to be universal. However, emerging research has revealed that many bacteria possess alternative features of their chemotaxis system, demonstrating that these systems are likely more complex than previously assumed. Here, we compare the canonical chemotaxis system of E. coli with systems that diverge in supramolecular architecture, sensory mechanisms, and protein composition. The alternative features have likely evolved to accommodate chemical specificities of natural niches and cell morphologies. Collectively, these studies demonstrate that bacterial chemotaxis systems are a rapidly expanding field that offers many new opportunities to explore this exceedingly diverse system.
We develop and study the hydrodynamic theory of flocking with autochemotaxis. This describes large collections of self-propelled entities all spontaneously moving in the same direction, each emitting a substance which attracts the others (e.g., ants). The theory combines features of the Keller-Segel model for autochemotaxis with the Toner-Tu theory of flocking. We find that sufficiently strong autochemotaxis leads to an instability of the uniformly moving state (the “flock”), in which bands of different density form moving parallel to the mean flock velocity with different speeds. This instability is, therefore, completely different from the well-known “banding instability,” in which bands form perpendicular to the mean flock velocity. The bands we find, which are reminiscent of ant trails, coarsen over time to reach a phase-separated state, in which one high-density and one low-density band fill the entire system. The same instability, described by the same hydrodynamic theory, can occur in flocks phase separating due to any microscopic mechanism (e.g., sufficiently strong attractive interactions). Although in many ways analogous to equilibrium phase separation via spinodal decomposition, the two steady-state densities here are determined not by a common tangent construction, as in equilibrium, but by an uncommon tangent construction very similar to that found for motility-induced phase separation of disordered active particles. Our analytic theory agrees well with our numerical simulations of our equations of motion.
Bacteria can tolerate antibiotics despite lacking the genetic components for resistance. The prevailing notion is that tolerance results from depleted cellular energy or cell dormancy. In contrast to this view, many cells in the tolerant population of Escherichia coli can exhibit motility – a phenomenon that requires cellular energy, specifically, the proton-motive force (PMF). As these motile-tolerant cells are challenging to isolate from the heterogeneous tolerant population, their survival mechanism is unknown. Here, we discovered that motile bacteria segregate themselves from the tolerant population under micro-confinement, owing to their unique ability to penetrate micron-sized channels. Single-cell measurements on the motile-tolerant population showed that the cells retained a high PMF, but they did not survive through active efflux alone. By utilizing growth assays, single-cell fluorescence studies, and chemotaxis assays, we showed that the cells survived by dynamically inhibiting the function of existing porins in the outer membrane. A drug transport model for porin-mediated intake and efflux pump-mediated expulsion suggested that energetic tolerant cells withstand antibiotics by constricting their porins. The novel porin adaptation we have uncovered is independent of gene expression changes and may involve electrostatic modifications within individual porins to prevent extracellular ligand entry.
Chemotaxis, or the following of chemical concentration gradients, is essential for microbes to locate nutrients. A microbe can swim in the direction of increasing nutrient concentrations to reach the source. However, microbes often display paradoxical behaviors, such as Escherichia coli being repulsed by several amino acids. Here, we explore chemotaxis towards a moving target and demonstrate that repulsion from a nutrient can actually improve chemotaxis towards its source. Because a moving source leaves most of the nutrient plume behind it, simply following the concentration gradient produces inefficient intercept trajectories. However, when attraction to a fast-diffusing molecule and repulsion from a slow-diffusing molecule are combined, motion in a new direction emerges and intercept times are significantly reduced. When the source is moving faster than the microbe can swim this differential strategy can even be essential to ever intercepting the source at all. Finally, we leverage existing data to show that E. coli is attracted to fast-diffusing amino acids and repulsed by slow-diffusing ones, suggesting it may utilize a differential strategy and providing a possible explanation for its repulsion from certain amino acids. Our results thus illuminate new possibilities in how microbes can integrate signals from multiple concentration gradients and propose a new strategy by which microbe may accomplish the difficult task of intercepting a moving target.
Bacteria perform chemotactic adaptation by sequential modification of multiple modifiable sites on chemoreceptors through stochastic action of tethered adaptation enzymes (CheR and CheB). To study the molecular kinetics of this process, we measured the response to different concentrations of MeAsp for the Tar-only Escherichia coli strain. We found a strong dependence of the methylation rate on the methylation level and established a new mechanism of adaptation kinetics due to tethered particle motion of the methylation enzyme CheR. Experiments with various lengths of the C-terminal flexible chain in the Tar receptor further validated this mechanism. The tethered particle motion resulted in a CheR concentration gradient that ensures encounter-rate matching of the sequential modifiable sites. An analytical model of multisite catalytic reaction showed that this enables robustness of methylation to fluctuations in receptor activity or cell-to-cell variations in the expression of adaptation enzymes and reduces the variation in methylation level among individual receptors.
The movement of cells in response to a chemical gradient is known as chemotaxis.An assay that is frequently used to analyze chemotaxis is the soft agar plate method. In this study, we used the soft agar plate method to examine the chemotactic migration of bacteria. On soft agar plates with a chemical attractant, bacteria were injected, and over time, their migration toward the attractant was seen. We discovered that the bacteria clearly responded to the attractant by migrating in that direction and producing discernible colonies. Our findings show how the soft agar plate approach may be used to examine the chemotactic behaviorof bacteria, and they also imply that it can be used to study the chemotactic behavior of other cell types. Chemotaxis is a biological mechanism in which specialized sensory receptors on the surface of bacteria detect chemical gradients. These receptors set off a series of events that alter the bacterial flagella motor and cause the bacterium to migrate in the direction of the chemical gradient. Several crucial bacterial processes, such as nutrition intake, host colonization, and biofilm formation, depend on chemotaxis.
About half of the known bacterial species perform chemotaxis that gains them access to sites that are optimal for growth and survival. The motility apparatus and chemotaxis signaling pathway impose a large energetic and metabolic burden on the cell. There is almost no limit to the type of chemoeffectors that are recognized by bacterial chemoreceptors. For example, they include hormones, neurotransmitters, quorum-sensing molecules, and inorganic ions. However, the vast majority of chemoeffectors appear to be of metabolic value. We review here the experimental evidence indicating that accessing nutrients is the main selective force that led to the evolution of chemotaxis.
The current assignment depicts the structure of recent quinoline derivatives. This method begins with the structure of imine derivatives through the condensation reaction of ethyl 2-aminobenzoate with various substituted aliphatic aldehydes and ketones in the existence of sodium hydroxide as a catalyst. While the second step includes the intra-cyclization process of the imine compounds in presence of a base like tertiary butoxide that resolute installs the hydroxyl- group on the bicyclic skeleton and aromatic amines. The molecular docking program Flare V4.0 was applied to investigate the biological activities of divers produced compounds against E.coli bacteria. Spectral data support the compounds of each the recent outputs acquired during this assignment.
The chemotaxis network, one of the most prominent prokaryotic sensory systems, is present in most motile bacteria and archaea. Although the conserved signaling core of the network is well characterized, ligand specificities of a large majority of diverse chemoreceptors encoded in bacterial genomes remain unknown. Here we performed a systematic identification and characterization of new chemoeffectors for the opportunistic pathogen Pseudomonas aeruginosa , which has 26 chemoreceptors possessing most of the common types of ligand binding domains. By performing capillary chemotaxis assays for a library of growth-promoting compounds, we first identified a number of novel chemoattractants of varying strength. We subsequently mapped specificities of these ligands by performing Förster resonance energy transfer (FRET) and microfluidic measurements for hybrids containing ligand binding domains of P. aeruginosa chemoreceptors and the signaling domain of the Escherichia coli Tar receptor. Direct binding of ligands to chemoreceptors was further confirmed in vitro using thermal shift assay and microcalorimetry. Altogether, the combination of methods enabled us to assign several new attractants, including methyl 4-aminobutyrate, 5-aminovalerate, L-ornithine, 2-phenylethylamine and tyramine, to previously characterized chemoreceptors and to annotate a novel purine-specific receptor PctP. Our screening strategy could be applied for the systematic characterization of unknown sensory domains in a wide range of bacterial species.
Importance
Chemotaxis of motile bacteria has multiple physiological functions. It enables bacteria to locate optimal ecological niches, mediates collective behaviors, and can play an important role in infection. These multiple functions largely depend on ligand specificities of chemoreceptors, and the number and identities of chemoreceptors show high diversity between organisms. Similar diversity is observed for the spectra of chemoeffectors, which include not only chemicals of high metabolic value but also bacterial, plant and animal signaling molecules. However, the systematic identification of chemoeffectors and their mapping to specific chemoreceptors remains a challenge. Here, we combined several in vivo and in vitro approaches to establish a systematic screening strategy for the identification of receptor ligands, and we applied it to identify a number of new physiologically relevant chemoeffectors for the important opportunistic human pathogen P. aeruginosa . This strategy can be equally applicable to map specificities of sensory domains from a wide variety of receptor types and bacteria.
Salmonella enterica has six subspecies, of which the subspecies enterica is the most important for human health. The dispersal and infectivity of this species are dependent upon flagella-driven motility. Two kinds of flagella-mediated movements have been described-swimming individually in bulk liquid and swarming collectively over a surface substrate. During swarming, the bacteria acquire a distinct physiology, the most significant consequence of which is acquisition of adaptive resistance to antibiotics. Described here are protocols to cultivate, verify, and study swimming and swarming motility in S. enterica, and an additional "border-crossing" assay, where cells "primed" to swarm are presented with an environmental challenge such as antibiotics to assess their propensity to handle the challenge.
Rotation is part of our everyday lives. For most of human history, rotation was considered a uniquely human invention, something beyond the anatomical capabilities of organisms. In 1973, Howard Berg made the audacious proposal that the common gut bacterium Escherichia coli swims by rotating helical flagellar filaments. In 1987, Paul Boyer suggested that the FoF1 ATP synthase of E. coli is also a rotary device. Now we know that rotating nanomachines evolved independently at least three times. They power a wide variety of cellular processes. Here, the study of flagellar rotation in E. coli is briefly summarized. In 2020, the Cryo-EM structure of the MotAB stator element of the bacterial flagellum was described. The structure strongly suggests that the MotAB stator rotates to drive flagellar rotation. Similar motors are coupled to other diverse processes. The following articles in this issue review the current knowledge and speculation about rotating biological nanomachines.
We describe a new method for accurately and reproducibly delivering a minute amount of a chemical to a small target in an aqueous environment. Our method is based on a micropipette with a check valve at its tip that can be opened and closed on demand. We demonstrate that this device can produce a flux of 10 ⁻¹² l in a short pulse lasting less than 100 ms. The finite width of the pulse is due to molecular dispersion of the chemical, in this case, fluorescein. The chemical distribution near the micropipette tip is measured and compared with the results of a numerical integration assuming stokeslet flow. Our technique is of general utility and has applications in microbiology and neuroscience when a precise control of the spatiotemporal chemical distribution around a specimen is desired.
Chemical sensing is vital to the survival of all organisms. Bacterial chemotaxis is conducted by multiple receptors that sense chemicals to regulate a single signalling system controlling the transition between the direction (clockwise vs. counterclockwise) of flagellar rotation. Such an integrated system seems better suited to judge chemicals as either favourable or unfavourable, but not for identification purposes though differences in their affinities to the receptors may cause difference in response strength. Here, an experimental setup was developed to monitor behaviours of multiple cells stimulated simultaneously as well as a statistical framework based on Bayesian inferences. Although responses of individual cells varied substantially, ensemble averaging of the time courses seemed characteristic to attractant species, indicating we can extract information of input chemical species from responses of the bacterium. Furthermore, two similar, but distinct, beverages elicited attractant responses of cells with profiles distinguishable with the Bayesian procedure. These results provide a basis for novel bio-inspired sensors that could be used with other cell types to sense wider ranges of chemicals.
The survival and successful spread of many bacterial species hinges on their mode of motility. One of the most distinct of these is swarming, a collective form of motility where a dense consortium of bacteria employ flagella to propel themselves across a solid surface. Surface environments pose unique challenges, derived from higher surface friction/tension and insufficient hydration. Bacteria have adapted by deploying an array of mechanisms to overcome these challenges. Beyond allowing bacteria to colonize new terrain in the absence of bulk liquid, swarming also bestows faster speeds and enhanced antibiotic resistance to the collective. These crucial attributes contribute to the dissemination, and in some cases pathogenicity, of an array of bacteria.
This mini-review highlights; 1) aspects of swarming motility that differentiates it from other methods of bacterial locomotion. 2) Facilitatory mechanisms deployed by diverse bacteria to overcome different surface challenges. 3) The (often difficult) approaches required to cultivate genuine swarmers. 4) The methods available to observe and assess the various facets of this collective motion, as well as the features exhibited by the population as a whole.
The past two decades have seen a remarkable progress in the development of synthetic colloidal agents which are capable of creating directed motion in an unbiased environment at the microscale. These self-propelling particles are often praised for their enormous potential to self-organize into dynamic nonequilibrium structures such as living clusters, synchronized superrotor structures or self-propelling molecules featuring a complexity which is rarely found outside of the living world. However, the precise mechanisms underlying the formation and dynamics of many of these structures are still barely understood, which is likely to hinge on the gaps in our understanding of how active colloids interact. In particular, besides showing comparatively short-ranged interactions which are well known from passive colloids (Van der Waals, electrostatic etc.), active colloids show novel hydrodynamic interactions as well as phoretic and substrate-mediated “osmotic” cross-interactions which hinge on the action of the phoretic field gradients which are induced by the colloids on other colloids in the system. The present article discusses the complexity and the intriguing properties of these interactions which in general are long-ranged, non-instantaneous, nonpairwise and non-reciprocal and which may serve as key ingredients for the design of future nonequilibrium colloidal materials. Besides providing a brief overview on the state of the art of our understanding of these interactions a key aim of this review is to emphasize open key questions and corresponding open challenges.
Chemotactic migration of bacteria—their ability to direct multicellular motion along chemical gradients—is central to processes in agriculture, the environment, and medicine. However, current understanding of migration is based on studies performed in bulk liquid, despite the fact that many bacteria inhabit tight porous media such as soils, sediments, and biological gels. Here, we directly visualize the chemotactic migration of Escherichia coli populations in well-defined 3D porous media in the absence of any other imposed external forcing (e.g., flow). We find that pore-scale confinement is a strong regulator of migration. Strikingly, cells use a different primary mechanism to direct their motion in confinement than in bulk liquid. Furthermore, confinement markedly alters the dynamics and morphology of the migrating population—features that can be described by a continuum model, but only when standard motility parameters are substantially altered from their bulk liquid values to reflect the influence of pore-scale confinement. Our work thus provides a framework to predict and control the migration of bacteria, and active matter in general, in complex environments.
Intimate cell contact and subsequent type three secretion system-dependent cell invasion are key steps in host colonization of Salmonella. Adhesion to complex glycostructures at the apical membrane of polarized cells is mediated by the giant adhesin SiiE. This protein is secreted by a type 1 secretion system (T1SS) and needs to be retained at the bacterial surface to exert its adhesive function. Here, we show that SiiE surface expression was linked to the presence of L aspartate sensed by the Salmonella-specific methyl-accepting chemotaxis protein CheM. Bacteria lacking CheM were attenuated for invasion of polarized cells, whereas increased invasion was seen with Salmonella exposed to the non-metabolizable aspartate analog α methyl-D, L aspartate (MeAsp). While components of the chemotaxis phosphorelay or functional flagella were dispensable for the increased invasion, CheM directly interacted with proteins associated with the SiiE T1SS arguing for a novel non-canonical signaling mechanism. As a result, CheM attractant signaling caused a shift from secreted to surface-retained and adhesion-competent SiiE. Thus, CheM controls the virulence function of SiiE in a precise spatio-temporal fashion depending on the host micro-milieu.
In the search for new antibacterial compounds, we repositioned an antimalarial compound class by derivatising it based on the so-called "eNTRy" rules for enhanced accumulation into Gram-negative bacteria. We designed, synthesised and evaluated a small library of amino acid modified compounds together with the respective Boc-protected analogues, leading to no substantial improvement in antibacterial activity against Escherichia coli wild-type K12, whereas more distinct activity differences were observed in E. coli mutant strains ΔtolC, D22, ΔacrB and BL21(DE3)omp8. A comparison of the activity results of the E. coli mutants with respect to the known rules related to enhanced activity against Gram-negative bacteria revealed that applicability of the rules is not always ensured. Out of the four amino acids used in this study, glycine derivatives showed highest antibacterial activity, although still suffering from efflux issues.
Two proteins, a galactose-binding protein and a leucine-binding protein, have been isolated from shock fluid of a mutant of Escherichia coli K12 that lacks galactokinase. They were purified by conventional methods to a homogeneous state as judged by electrophoresis on acrylamide columns and other physicochemical criteria. The leucine-binding protein was crystallized by treatment with ammonium sulfate. Binding activity was measured by means of equilibrium dialysis. The osmotic shock procedure was an essential part of the scheme of purification.
The purified galactose-binding protein was substantially free of galactokinase, acid hexose phosphatase, and uridine diphosphoglucose pyrophosphatase activities. Of a number of carbohydrates tested, only galactose and glucose were bound. A number of related sugars, including mannose, fucose, lactose, galactosamine, and galactose 1- and 6-phosphate did not interfere with the binding of galactose. The leucine-binding protein showed specificity for leucine, isoleucine, and valine but not for other amino acids tested.
Dissociation constants were measured for the galactose-binding protein with galactose and glucose. The values were in the range of 10⁻⁶m. The binding proteins carried out a reversible binding of galactose or leucine in the absence of any chemical alteration of the substrates.
Cold osmotic shock following treatment with Tris-EDTA liberates two galactose binding components from the cell envelope of E. coli. One of them, most probably identical with the so-called galactose binding protein, is shown to be related to the function of the β-methylgalactoside permease in E. coli.
Galactose and β-glycerolgalactoside, the most efficiently transported substrates of the permease, show apparent Km values of uptake which are of the same order of magnitude as the dissociation constants of these sugars to the galactose binding protein. Glucose, β-glycerolgalactoseide, β-methylgalactoside and d-fucose inhibit the galactose uptake by the β-methylgalactoside permease in the same decreasing order as they inhibit the galactose binding activity of the galactose binding protein.
Two out of three permease-less mutants contain the binding protein. The binding protein isolated from these mutants appears to be identical to the corresponding binding protein from the permease positive strain by their immunochemical behavior as well as by their galactose binding activity.
The second galactose binding component also binds β-glycerolgalactoside. Its dissociation constant to galactose is higher than that of the galactose binding protein; its 280/260 mμ absorption ratio is 0.85.
N-methyl-N′-nitro-N-nitrosoguanidine (NTG) induces at least one mutation per treated cell under conditions permitting over 50 per cent survival. The procedure for obtaining these results is to take logarithmic phase cells from either nutrient broth or minimal medium, wash them, and treat them with 100 μg of NTG per ml of buffer at pH 6.0 for 15 to 30 minutes. Prior to plating, the cells are again washed, and - if auxotrophs are sought - are diluted into nutrient broth and permitted to undergo two division cycles.With this procedure the yield of induced auxotrophs is 11 per cent; at 1000 pg NTG per ml the yield is over 40 per cent, but 95 per cent of the cells are killed.
Extensive metabolism of chemicals is neither required, nor sufficient, for attraction of bacteria to the chemicals. Instead, the bacteria detect the attractants themselves. The systems that carry out this detection are called "chemoreceptors." There are mutants that fail to be attracted to one particular chemical or to a group of closely related chemicals but still metabolize these chemicals normally. These mutants are regarded as being defective in specific chemoreceptors. Data obtained so far indicate that there are at least five different chemoreceptors in Escherichia coli. The chemoreceptors are not the enzymes that catalyze the metabolism of the attractants, nor are they the parts of the permeases and related transport systems that have been tested.
Mutants of Escherichia coli K12 have been found which fail to carry out chemotaxis toward certain chemicals only. One mutant exhibits greatly reduced chemotaxis toward L-serine but has no detectable defect either in uptake or in oxidative metabolism of that compound. Another mutant is not attracted to D-galactose and certain related sugars. There is a correlation between the galactose chemotaxis defect and a defect in galactose uptake, perhaps indicating a common component for chemotaxis and uptake systems. The results are discussed in terms of a model for chemotaxis in which attractants are detected by specific "chemoreceptors."
THE bacterium Escherichia coli is chemotactic, that is, motile cells are attracted by certain chemicals such as oxygen, some sugars, and some amino-acids12. The chemicals are detected by “chemoreceptors", sensing devices which recognize an attractant without metabolizing it2. There are at least eight different chemoreceptors in E. coli2. Each chemoreceptor should have a recognition component-a part that has affinity for the chemicals detected by that chemoreceptor-and possibly other components to link the recognition component to a pathway, common to all the chemoreceptors2,3, that leads to the response.We have isolated “specifically nonchemotactic” mutants, which are defective in a particular chemoreceptor, so that they do not respond to a group of structurally related compounds but exhibit normal responses to other attractants4. For example, “galactose taxis” mutants4 have no detectable taxis toward D-galactose, 1-D-glycerol-ß-D-galactoside, D-fucose, methyl-ß-D-galactoside, L-arabinose, D-xylose, or L-sorbose (the sugars recognized only by the galactose chemoreceptor), and a reduced response toward D-glucose, methyl-a-D-glucoside and 2-deoxy-D-glucose (the sugars recognized by both the galactose and the glucose chemoreceptors). Taxis toward other sugar attractants (such as D-ribose) and toward amino-acids is normal in such a mutant.
Motile Escherichia coli placed at one end of a capillary tube containing an energy source and oxygen migrate out into the tube in one or two bands, which are clearly visible to the naked eye and can also be demonstrated by photography, microscopy, and densitometry and by assaying for bacteria throughout the tube. The formation of two bands is not due to heterogeneity among the bacteria, since the bacteria in each band, when reused, will form two more bands.
If an anaerobically utilizable energy source such as galactose is present in excess over the oxygen, the first band consumes all the oxygen and a part of the sugar and the second band uses the residual sugar anaerobically. On the other hand, if oxygen is present in excess over the sugar, the first band oxidizes all the sugar and leaves behind unused oxygen, and the second band uses up the residual oxygen to oxidize an endogenous energy source.
The essence of the matter is that the bacteria create a gradient of oxygen or of an energy source, and then they move preferentially in the direction of the higher concentration of the chemical. As a consequence, bands of bacteria (or rings of bacteria in the case of agar plates) form and move out. These results show that E. coli is chemotactic toward oxygen and energy sources such as galactose, glucose, aspartic acid, threonine, or serine. The full repertoire of chemotactic responses by E. coli is no doubt greater than this, and a more complete list remains to be compiled.
The studies reported here demonstrate that chemotaxis allows bacteria to find that environment which provides them with the greatest supply of energy. It is clearly an advantage for bacteria to be able to carry out chemotaxis, since by this means they can avoid unfavorable conditions and seek optimum surroundings.
Finally, it is necessary to acknowledge the pioneering work of Englemann, Pfeffer, and the other late-19th-century biologists who discovered chemotaxis in bacteria, and to point out that the studies reported here fully confirm the earlier reports of Beijerinck and Sherris and his collaborators on a band of bacteria chemotactic toward oxygen. By using a chemically defined medium instead of a complex broth, it has been possible to study this band more closely and to demonstrate in addition the occurrence of a second band of bacteria chemotactic toward an energy source. Beijerinck did, in fact, sometimes observe a second band, but he did not offer an explanation for it.
Adler, Julius (University of Wisconsin, Madison). Effect of amino acids and oxygen on chemotaxis in Escherichia coli. J. Bacteriol.
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121–129. 1966.—Motile cells of Escherichia coli placed at one end of a capillary tube containing a mixture of the 20 amino acids commonly found in proteins migrate out into the tube in two bands. The bands are clearly visible to the naked eye, and they can also be demonstrated by microscopy, photography, and densitometry, and by assaying for bacteria throughout the tube. The occurrence of more than one band is not due to heterogeneity among the bacteria, since each band can be used over to give rise to two again. The first band uses all the oxygen to oxidize portions of one or more of the amino acids, including serine, and the second band consumes the residual serine anaerobically. The results are interpreted to mean that E. coli shows chemotaxis toward oxygen and serine. When no energy source is added to the medium, a band of bacteria still appears. It consumes all the oxygen to oxidize an endogenous energy source. The addition of any one of 10 oxidizable amino acids stimulates the rate of travel of this band. Alanine, an example that was studied in detail, supports such a band that consumes all the oxygen to oxidize a portion of the alanine. Serine, the only amino acid that this strain can use either aerobically or anaerobically when grown under the conditions used here, gives rise to two bands.
We have isolated 40 mutants of Escherichia coli which are nonchemotactic as judged by their failure to swarm on semisolid tryptone plates or to make bands in capillary tubes containing tryptone broth. All the mutants have normal flagella, a fact shown by their shape and reaction with antiflagella serum. All are fully motile under the microscope and all are sensitive to the phage chi. Unlike its parent, one of the mutants, studied in greater detail, failed to show chemotaxis toward oxygen, glucose, serine, threonine, or aspartic acid. The failure to exhibit chemotaxis does not result from a failure to use the chemicals. The swimming of this mutant was shown to be random. The growth rate was normal under several conditions, and the growth requirements were unchanged.
Beobachtungen und Betrachtungen uiber tactische Reizerscheinungen
- W Rothert
- Rothert W.
Rothert, W. 1901. Beobachtungen und Betrachtungen uiber tactische Reizerscheinungen. Flora 88:371-421.
Solubilities of amino acids in water at various temperatures, p. B-10 Handbook of biochemistry: selected data for molecular biology
- J O Hutchens
- E P K Hade
Hutchens, J. O., and E. P. K. Hade, Jr. 1968. Solubilities of amino acids in water at various temperatures,
p. B-10. In H. A. Sober (ed.), Handbook of biochemistry: selected data for molecular biology. The Chemical Rubber Co., Cleveland.
Handbook of biochemistry: selected data for molecular biology. The Chemical Rubber Co
- J O Hutchens
- E P K Hade