[Show abstract][Hide abstract] ABSTRACT: Metal acquisition and intracellular trafficking are crucial for all cells and metal ions have been recognized as virulence determinants in bacterial pathogens. Virulence of the human gastric pathogen Helicobacter pylori is dependent on nickel, cofactor of two enzymes essential for in vivo colonization, urease and [NiFe] hydrogenase. We found that two small paralogous nickel-binding proteins with high content in Histidine (Hpn and Hpn-2) play a central role in maintaining non-toxic intracellular nickel content and in controlling its intracellular trafficking. Measurements of metal resistance, intracellular nickel contents, urease activities and interactomic analysis were performed. We observed that Hpn acts as a nickel-sequestration protein, while Hpn-2 is not. In vivo, Hpn and Hpn-2 form homo-multimers, interact with each other, Hpn interacts with the UreA urease subunit while Hpn and Hpn-2 interact with the HypAB hydrogenase maturation proteins. In addition, Hpn-2 is directly or indirectly restricting urease activity while Hpn is required for full urease activation. Based on these data, we present a model where Hpn and Hpn-2 participate in a common pathway of controlled nickel transfer to urease. Using bioinformatics and top-down proteomics to identify the predicted proteins, we established that Hpn-2 is only expressed by H. pylori and its closely related species Helicobacter acinonychis. Hpn was detected in every gastric Helicobacter species tested and is absent from the enterohepatic Helicobacter species. Our phylogenomic analysis revealed that Hpn acquisition was concomitant with the specialization of Helicobacter to colonization of the gastric environment and the duplication at the origin of hpn-2 occurred in the common ancestor of H. pylori and H. acinonychis. Finally, Hpn and Hpn-2 were found to be required for colonization of the mouse model by H. pylori. Our data show that during evolution of the Helicobacter genus, acquisition of Hpn and Hpn-2 by gastric Helicobacter species constituted a decisive evolutionary event to allow Helicobacter to colonize the hostile gastric environment, in which no other bacteria persistently thrives. This acquisition was key for the emergence of one of the most successful bacterial pathogens, H. pylori.
[Show abstract][Hide abstract] ABSTRACT: Background
Phosphatidylinositol-3-kinases (PI3Ks) are a family of eukaryotic enzymes modifying phosphoinositides in phosphatidylinositols-3-phosphate. Located upstream of the AKT/mTOR signalling pathway, PI3Ks activate secondary messengers of extracellular signals. They are involved in many critical cellular processes such as cell survival, angiogenesis and autophagy. PI3K family is divided into three classes, including 14 human homologs. While class II enzymes are composed of a single catalytic subunit, class I and III also contain regulatory subunits. Here we present an in-depth phylogenetic analysis of all PI3K proteins.
We confirmed that PI3K catalytic subunits form a monophyletic group, whereas regulatory subunits form three distinct groups. The phylogeny of the catalytic subunits indicates that they underwent two major duplications during their evolutionary history: the most ancient arose in the Last Eukaryotic Common Ancestor (LECA) and led to the emergence of class III and class I/II, while the second – that led to the separation between class I and II – occurred later, in the ancestor of Unikonta (i.e., the clade grouping Amoebozoa, Fungi, and Metazoa). These two major events were followed by many lineage specific duplications in particular in vertebrates, but also in various protist lineages. Major loss events were also detected in Vidiriplantae and Fungi. For the regulatory subunits, we identified homologs of class III in all eukaryotic groups indicating that, for this class, both the catalytic and the regulatory subunits were presents in LECA. In contrast, homologs of the regulatory class I have a more recent origin.
The phylogenetic analysis of the PI3K shed a new light on the evolutionary history of these enzymes. We found that LECA already contained a PI3K class III composed of a catalytic and a regulatory subunit. Absence of class II regulatory subunits and the recent origin of class I regulatory subunits is puzzling given that the class I/II catalytic subunit was present in LECA and has been conserved in most present-day eukaryotic lineages. We also found surprising major loss and duplication events in various eukaryotic lineages. Given the functional specificity of PI3K proteins, this suggests dynamic adaptation during the diversification of eukaryotes.
Electronic supplementary material
The online version of this article (doi:10.1186/s12862-015-0498-7) contains supplementary material, which is available to authorized users.
Preview · Article · Dec 2015 · BMC Evolutionary Biology
[Show abstract][Hide abstract] ABSTRACT: Background
Two-component systems (TCS) play critical roles in sensing and responding to environmental cues. Azospirillum is a plant growth-promoting rhizobacterium living in the rhizosphere of many important crops. Despite numerous studies about its plant beneficial properties, little is known about how the bacterium senses and responds to its rhizospheric environment. The availability of complete genome sequenced from four Azospirillum strains (A. brasilense Sp245 and CBG 497, A. lipoferum 4B and Azospirillum sp. B510) offers the opportunity to conduct a comprehensive comparative analysis of the TCS gene family.
Azospirillum genomes harbour a very large number of genes encoding TCS, and are especially enriched in hybrid histidine kinases (HyHK) genes compared to other plant-associated bacteria of similar genome sizes. We gained further insight into HyHK structure and architecture, revealing an intriguing complexity of these systems. An unusual proportion of TCS genes were orphaned or in complex clusters, and a high proportion of predicted soluble HKs compared to other plant-associated bacteria are reported. Phylogenetic analyses of the transmitter and receiver domains of A. lipoferum 4B HyHK indicate that expansion of this family mainly arose through horizontal gene transfer but also through gene duplications all along the diversification of the Azospirillum genus. By performing a genome-wide comparison of TCS, we unraveled important ‘genus-defining’ and ‘plant-specifying’ TCS.
This study shed light on Azospirillum TCS which may confer important regulatory flexibility. Collectively, these findings highlight that Azospirillum genomes have broad potential for adaptation to fluctuating environments.
Electronic supplementary material
The online version of this article (doi:10.1186/s12864-015-1962-x) contains supplementary material, which is available to authorized users.
[Show abstract][Hide abstract] ABSTRACT: In a recent article, Nelson-Sathi et al. (NS) report that the origins of major archaeal lineages (MAL) correspond to massive
group-specific gene acquisitions via HGT from bacteria (Nelson-Sathi et al. 2015. Origins of major archaeal clades correspond
to gene acquisitions from bacteria. Nature 517(7532):77-80.). If correct, this would have fundamental implications for the
process of diversification in microbes. However, a reexamination of these data and results shows that the methodology used
by NS systematically inflates the number of genes acquired at the root of each MAL, and incorrectly assumes bacterial origins
for these genes. A reanalysis of their data with appropriate phylogenetic models accounting for the dynamics of gene gain
and loss between lineages supports the continuous acquisition of genes over long periods in the evolution of Archaea.
Full-text · Article · Nov 2015 · Molecular Biology and Evolution
[Show abstract][Hide abstract] ABSTRACT: Acid mine drainage (AMD) is a highly toxic environment for most living organisms due to the
presence of many lethal elements including arsenic (As). Thiomonas (Tm.) bacteria are found
ubiquitously in AMD and can withstand these extreme conditions, in part because they are
able to oxidize arsenite. In order to further improve our knowledge concerning the adaptive
capacities of these bacteria, we sequenced and assembled the genome of six isolates
derived fromthe Carnoulès AMD, and compared them to the genomes of Tm. arsenitoxydans
3As (isolated from the same site) and Tm. intermedia K12 (isolated from a sewage pipe). A
detailed analysis of the Tm. sp. CB2 genome revealed various rearrangements had occurred
in comparison to what was observed in 3As and K12 and over 20 genomic islands (GEIs)
were found in each of these three genomes.We performed a detailed comparison of the two
arsenic-related islands found in CB2, carrying the genes required for arsenite oxidation and
As resistance, with those found in K12, 3As, and five other Thiomonas strains also isolated
from Carnoulès (CB1, CB3, CB6, ACO3 and ACO7). Our results suggest that these arsenicrelated
islands have evolved differentially in these closely related Thiomonas strains, leading
to divergent capacities to survive in As rich environments.
[Show abstract][Hide abstract] ABSTRACT: Author Summary
Deciphering the circuit design of signal transduction networks is a fundamental question in cell biology. This task is challenging because many pathways are branched and control multiple cellular processes in response to one or several environmental signals. Studying pathway diversification in bacteria could be a powerful approach because these organisms contain so-called chemosensory systems, modular signaling units that have been adapted multiple times independently to regulate a large number of physiological processes. Here, we studied one such system, the Myxococcus xanthus chemosensory pathway (Frz) that controls the directionality of two distinct motility systems (A- and S-motility). By experimentally uncoupling the regulations, we found that the Frz pathway evolved from a simpler ancestral system that only controlled S-motility originally. Two major pathway remodeling events allowed the recruitment of A-motility to the regulation, (i) the duplication of a connector protein which created the branch point and (ii), the acquisition of a signal amplification mechanism to allow signal partitioning at the branch point. These results reveal the core structure of a complex chemosensory system and generally suggest that gene duplication and signal amplification underlie the diversification of signal transduction pathways.
[Show abstract][Hide abstract] ABSTRACT: One of the most fundamental questions in evolutionary biology is the origin of the lineage leading to eukaryotes. Recent phylogenomic analyses have indicated an emergence of eukaryotes from within the radiation of modern Archaea and specifically from a group comprising Thaumarchaeota/"Aigarchaeota" (candidate phylum)/Crenarchaeota/Korarchaeota (TACK). Despite their major implications, these studies were all based on the reconstruction of universal trees and left the exact placement of eukaryotes with respect to the TACK lineage unclear. Here we have applied an original two-step approach that involves the separate analysis of markers shared between Archaea and eukaryotes and between Archaea and Bacteria. This strategy allowed us to use a larger number of markers and greater taxonomic coverage, obtain high-quality alignments, and alleviate tree reconstruction artifacts potentially introduced when analyzing the three domains simultaneously. Our results robustly indicate a sister relationship of eukaryotes with the TACK superphylum that is strongly associated with a distinct root of the Archaea that lies within the Euryarchaeota, challenging the traditional topology of the archaeal tree. Therefore, if we are to embrace an archaeal origin for eukaryotes, our view of the evolution of the third domain of life will have to be profoundly reconsidered, as will many areas of investigation aimed at inferring ancestral characteristics of early life and Earth.
Full-text · Article · May 2015 · Proceedings of the National Academy of Sciences
[Show abstract][Hide abstract] ABSTRACT: Mesotoga strain PhosAc3 was the first mesophilic cultivated member of the order Thermotogales. This genus currently contain two described species, M. prima and M. infera. Strain PhosAc3, isolated from a Tunisian digestor treating phosphogypsum, is phylogenetically closely related to M. prima strain MesG1.Ag.4.2T. Strain PhosAc3 has a genome of 3.1 Mb with a G+C content of 45.2%. It contains 3,051 protein-coding genes of which 74.6% have their best reciprocal BLAST hit in the genome of the type species, strain MesG1.Ag.4.2T. For this reason we propose to assign strain PhosAc3 as a novel ecotype of the Mesotoga prima species. However, in contrast with the M. prima type strain, (i) it does not ferment sugars but uses them only in the presence of elemental sulfur as terminal electron acceptor, (ii) it produces only acetate and CO2 from sugars, whereas strain MesG1.Ag.4.2T produces acetate, butyrate, isobutyrate, isovalerate, 2-methyl-butyrate and (iii) sulfides are also end products of the elemental sulfur reduction in theses growth conditions.
Electronic supplementary material
The online version of this article (doi:10.1186/1944-3277-10-12) contains supplementary material, which is available to authorized users.
Full-text · Article · May 2015 · Standards in Genomic Sciences
[Show abstract][Hide abstract] ABSTRACT: Studying the evolution of macromolecular assemblies is important to improve our understanding of how complex cellular structures evolved, and to identify the functional building blocks that are involved. Recent studies suggest that the macromolecular complexes that are involved in two distinct processes in Myxococcus xanthus - surface motility and sporulation - are derived from an ancestral polysaccharide capsule assembly system. In this Opinion article, we argue that the available data suggest that the motility machinery evolved from this capsule assembly system following a gene duplication event, a change in carbohydrate polymer specificity and the acquisition of additional proteins by the motility complex, all of which are key features that distinguish the motility and sporulation systems. Furthermore, the presence of intermediates of these systems in bacterial genomes suggests a testable evolutionary model for their emergence and spread.
[Show abstract][Hide abstract] ABSTRACT: Microorganisms were the sole inhabitants of our planet for almost 3 billion years. They have survived the intense geological upheavals that have marked the history of the Earth. They profoundly shaped their environment, thus participating in a true co-evolution between the biosphere and the geosphere. Through their activity, they also created favourable conditions for the emergence of multicellular aerobic organisms (particularly with an intense production of oxygen released into the atmosphere).
Among past microorganisms, LUCA occupied a central position in the evolutionary history of life. The possible origin and the large uncertainties about the nature of LUCA are discussed: where and when did LUCA live? Was it a hyperthermophilic, thermophilic or mesophilic organism? How did its genome look like?
Scenarios and hypotheses regarding the emergence and the relationships of the three domains of life – Archaea, Bacteria and Eucarya – as well as the transition from a prokaryotic to eukaryotic cell organisation are discussed in the light of the most recent data. Possible major steps in the evolution of microorganisms are deduced from genomic investigations and from the geological record (fossils, isotopic ratios, biomarkers). Although the early steps of microbial metabolic evolution are still hotly debated, it is possible to speculate on the occurrence of the first living entities, from the primordial metabolisms to the advent of photosynthesis.
[Show abstract][Hide abstract] ABSTRACT: Microorganisms live in fluctuating environments. At the microscopic scale, their habitats are contrasted and have highly variable physical, chemical, and biological parameters. The versatility of microbial ecosystems implies that microorganisms must constantly adapt to these. Adaptation can result from spontaneous point mutations of the genetic material that creates genetic diversity at the population level. However, this mechanism by itself is not capable of explaining the extraordinary adaptive capacity of microorganisms. Research performed in the first part of the twentieth century has revealed that this capacity results very often from the ability to import genetic material from other microorganisms. This phenomenon is called horizontal (or lateral) gene transfer (HGT). The mechanisms of HGTs and their evolutionary consequences are discussed..
[Show abstract][Hide abstract] ABSTRACT: Classification of prokaryotes is hierarchically organized into seven levels: kingdoms, phyla, classes, orders, families, genera, and species. In prokaryotes, because they reproduce by clonal fission, the species, considered as the basic unit of the biological diversity, faces several problems such as the definition of an individual. A bacterial strain can be recognized as an individual belonging to a species. However, many inconsistencies exist between phenotypic similarity levels and evolutionary relationships deduced from molecular phylogenies. Most taxonomic groups have been reconsidered through phylogenetic analysis in the 1980s, and a consensus has been reached on the need for coherence between taxonomy and phylogeny. Thus, the multiple revisions of species, genera, or higher taxonomic levels pose many complex problems that are solved gradually. Prokaryotic microorganisms correspond to two of the three domains of life: Archaea and Bacteria. Their systematics is described in the “Bergey’s Manual for Systematic Bacteriology, second edition” published in five volumes.
In the text, the Latin terms used are those accepted by the Nomenclature Committee, and the organization of the bacterial and archaeal domains is presented as they appear in the “Bergey’s Manual for Systematic Bacteriology.” They are discussed according to the recent data of the hierarchical classification of Prokaryotes.
[Show abstract][Hide abstract] ABSTRACT: In human pathogenic bacteria, nickel is required for the activation of two enzymes, urease and [NiFe]-hydrogenase, necessary for host infection. Acquisition of Ni(II) is mediated by either permeases or ABC-importers, the latter including a subclass that involves an extracytoplasmic nickel-binding protein, Ni-BP. This study reports on the structure of three Ni-BPs from a diversity of human pathogens and on the existence of three new nickel-binding motifs. These are different from that previously described for Escherichia coli Ni-BP NikA, known to bind nickel via a nickelophore, and indicate a variegated ligand selectivity for Ni-BPs. The structures are consistent with ligand affinities measured in solution by calorimetry and challenge the hypothesis of a general requirement of nickelophores for nickel uptake by canonical ABC importers. Phylogenetic analyses showed that Ni-BPs have different evolutionary origins and emerged independently from peptide-binding proteins, possibly explaining the promiscuous behavior of this class of Ni(II) carriers.
[Show abstract][Hide abstract] ABSTRACT: The seminal work of Carl Woese and co-workers has contributed to promote the RNA component of the small subunit of the ribosome (SSU rRNA) as a "gold standard" of modern prokaryotic taxonomy and systematics, and an essential tool to explore microbial diversity. Yet, this marker has a limited resolving power, especially at deep phylogenetic depth and can lead to strongly biased trees. The ever-larger number of available complete genomes now calls for a novel standard dataset of robust protein markers that may complement SSU rRNA. In this respect, concatenation of ribosomal proteins (r-proteins) is being growingly used to reconstruct large-scale prokaryotic phylogenies, but their suitability for systematic and/or taxonomic purposes has not been specifically addressed. Using Proteobacteria as a case study, we show that amino acid and nucleic acid r-protein sequences contain a reliable phylogenetic signal at a wide range of taxonomic depths, which has not been totally blurred by mutational saturation or horizontal gene transfer. The use of accurate evolutionary models and reconstruction methods allows overcoming most tree reconstruction artefacts resulting from compositional biases and/or fast evolutionary rates. The inferred phylogenies allow clarifying the relationships among most proteobacterial orders and families, along with the position of several unclassified lineages, suggesting some possible revisions of the current classification. In addition, we investigate the root of the Proteobacteria by considering the time-variation of nucleic acid composition of r-protein sequences and the information carried by horizontal gene transfers, two approaches that do not require the use of an outgroup and limit tree reconstruction artefacts. Altogether, our analyses indicate that r-proteins may represent a promising standard for prokaryotic taxonomy and systematics.
Full-text · Article · Jun 2014 · Molecular Phylogenetics and Evolution
[Show abstract][Hide abstract] ABSTRACT: The thermophilic sulfate-reducing archaeon Archaeoglobus fulgidus strain VC-16 (DSM 4304), which is known to oxidize fatty acids and n-alkenes, was shown to oxidize saturated hydrocarbons (n-alkanes in the range C10-C21) with thiosulfate or sulfate as a terminal electron acceptor. The amount of n-hexadecane degradation observed was in stoichiometric agreement with the theoretically expected amount of thiosulfate reduction. One of the pathways used by anaerobic microorganisms to activate alkanes is addition to fumarate that involves alkylsuccinate synthase as a key enzyme. A search for genes encoding homologous enzymes in A. fulgidus identified the pflD gene (locus-tag AF1449) that was previously annotated as a pyruvate formate lyase. A phylogenetic analysis revealed that this gene is of bacterial origin and was likely acquired by A. fulgidus from a bacterial donor through a horizontal gene transfer. Based on three-dimensional modeling of the corresponding protein and molecular dynamic simulations, we hypothesize an alkylsuccinate synthase activity for this gene product. The pflD gene expression was upregulated during the growth of A. fulgidus on an n-alkane (C16) compared with growth on a fatty acid. Our results suggest that anaerobic alkane degradation in A. fulgidus may involve the gene pflD in alkane activation through addition to fumarate. These findings highlight the possible importance of hydrocarbon oxidation at high temperatures by A. fulgidus in hydrothermal vents and the deep biosphere.The ISME Journal advance online publication, 24 April 2014; doi:10.1038/ismej.2014.58.
[Show abstract][Hide abstract] ABSTRACT: The evolutionary origin of eukaryotes is a question of great interest for which many different hypotheses have been proposed. These hypotheses predict distinct patterns of evolutionary relationships for individual genes of the ancestral eukaryotic genome. The availability of numerous completely sequenced genomes covering the three domains of life makes it possible to contrast these predictions with empirical data. We performed a systematic analysis of the phylogenetic relationships of ancestral eukaryotic genes with archaeal and bacterial genes. In contrast with previous studies, we emphasize the critical importance of methods accounting for statistical support, horizontal gene transfer and gene loss, and we disentangle the processes underlying the phylogenomic pattern we observe. We first recover a clear signal indicating that a fraction of the bacteria-like eukaryotic genes are of alphaproteobacterial origin. Then, we show that the majority of bacteria-related eukaryotic genes actually do not point to a relationship with a specific bacterial taxonomic group. We also provide evidence that eukaryotes branch close to the last archaeal common ancestor. Our results demonstrate that there is no phylogenetic support for hypotheses involving a fusion with a bacterium other than the ancestor of mitochondria. Overall, they leave only two possible interpretations, based respectively on the early-mitochondria hypotheses, which suppose an early endosymbiosis of an alphaproteobacterium in an archaeal host, and on the slow-drip autogenous hypothesis, in which early eukaryotic ancestors were particularly prone to horizontal gene transfers.
Full-text · Article · Jan 2014 · Molecular Biology and Evolution