Article

Engineering a microbial ‘trap and release’ mechanism for microplastics removal

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Abstract

Plastics are discarded and accumulated in the environment at an alarming rate. However, their resistance to biodegradation allows them to persist in the environment for prolonged durations. While large plastics are easier to remove, microplastic particles from cosmetics or fragments from larger pieces are extremely difficult to remove from the environment. Furthermore, current techniques such as filters poorly retain microplastics or require harsh chemical treatments in wastewater treatment plants. Hence, microplastics enter the natural environment easily even after effluent treatments, thereby endangering aquatic life and humans who consume seafood. It is imperative to develop sustainable bioaggregation processes to trap microplastics quickly for easier removal from the environment. Here, we showed that microplastics can be trapped and aggregated in the sticky exopolymeric substances (EPS) produced by biofilms. As a proof-of-concept, we engineered a bacterial biofilm with a ‘capture-release mechanism’, whose EPS can first cause bioaggregation of microplastics for easier isolation, followed by an inducible biofilm dispersal mechanism that releases trapped microplastics for downstream resource recovery. We also demonstrated the potential application of the engineered biofilm in mitigating microplastics pollution in seawater samples collected in the vicinity of a sewage outfall. This capture-and-release approach should prove widely applicable to other micropollutants or biofilm-enabled catalysis.

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... These sticky bacteria can create multicellular biofilms on the surface of MPs using their own exopolymeric matrix, which frequently had changed diversity, metabolism, and function. This ability makes microbe nets on the MPs surfaces that can easily collect MPs from polluted sources [195][196][197][198]. Additionally, easy plastic recovery from bioaggregation may encourage recycling of recovered plastics rather than using landfills or incineration [199]. ...
... The core mechanisms involved in the removal of MPs/NPs through biofilm includes electrostatic surface adsorption, hydrophobic interaction, sorption onto the biofilm layer, intermolecular repulsion, and electrostatic interplay between MPs/NPs and the membrane surface [170]. Liu et al. [199] have developed a remarkable bacterial biofilm with a "traprelease mechanism" to tackle microplastic pollution. The biofilm, using exopolymeric substances (EPS) and controlled by the signaling molecule c-di-GMP, efficiently aggregates microplastics for easy removal. ...
Article
Micro-and nanoplastics (MNPs) are a growing source of pollution from natural and plastic fibers to non-fiber particles in water matrices. The current review highlights the detection, pathways, measurements and fate of MNPs. Besides, it addresses various treatment technologies, the next generation of MNPs degradation and their removal mechanisms from water bodies especially stormwater. The removal efficiency of MNPs decreases with decreasing particle size, as smaller particles were able to pass more easily through the tertiary sand filter or membrane filter. NPs exhibited lower removal efficiency compared to MPs. Conventional methods for treating stormwater including bioretention filters and constructed wetlands are inadequate in removing MNPs effectively. Some novel methods, such as egg protein derived ultra-lightweight hybrid monolithic aerogel, rely solely on gravity and do not require water, demonstrating up to 100 % removal of microplastics from seawater. This method could also be applied to stormwater treatment. This is superior to membrane technologies including UF and MF, which operates with a substantial energy input and excess water. Integrated treatment systems that combine different technologies can overcome the limitations of individual methods. Furthermore, the core mechanisms involved in eliminating MPs/NPs via biofilm consist of electrostatic surface attachment, hydro-phobic interaction, absorption onto the biofilm layer, intermolecular repulsion, and electrostatic interaction between MPs/NPs and the membrane surface.
... Whilst Romero and co-workers used the wild-type strain PAO1, Liu et al. [89] and Chan et al. [90] engineered the chassis organism P. aeruginosa to perform the capture and release steps. Both exploit the secondary signalling messenger c-di-GMP, which is strongly implicated in biofilm formation in the chassis organism [91]. ...
... In the first example, Liu et al. targeted the wsp chemosensory pathway that is inextricably linked to intracellular levels of c-di-GMP [89]. The authors engineered a wsp mutant, ΔwspF, that overexpresses c-di-GMP. ...
Article
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The global plastic waste crisis has triggered the development of novel methods for removal of recalcitrant polymers from the environment. Biotechnological approaches have received particular attention due to their potential for enabling sustainable, low-intensity bioprocesses which could also be interfaced with microbial upcycling pathways to support the emerging circular bioeconomy. However, low biodegradation efficiency of solid plastic materials remains a bottleneck, especially at mesophilic conditions required for one-pot degradation and upcycling. A promising strategy used in nature to address this is localisation of plastic-degrading microbes to the plastic surface via biofilm-mediated surface association. This review highlights progress and opportunities in leveraging these naturally occurring mechanisms of biofilm formation and other cell-surface adhesion biotechnologies to co-localise engineered cells to plastic surfaces. We further discuss examples of combining these approaches with extracellular expression of plastic-degrading enzymes to accelerate plastic degradation. Additionally, we review this topic in the context of nano- and microplastics bioremediation and their removal from wastewater and finally propose future research directions for this nascent field.
... Conventional microplastics (not fibrous, mainly) are primarily made from partially degraded polyolefins, which, due to their low-density, float on water. To leads to their easy detection and simple methods of capturing them [6]. ...
... Fibrous microplastics are released from textiles by several mechanisms. The first stage is the release of the dust (nanoplastics and particles deposited on the surface as waxes in the case of cotton) [6] from abraded fibrous materials' surfaces and short fibers as part of the surface's hairiness. Surface hairiness is typical for linear staple fiber structures (yarns) (composed fibers are usually over 1.5 cm in length) and for corresponding planar or 3D fibrous structures of these semi-products. ...
Article
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More than a third of microplastics in surface waters are formed by microplastics released from textile products containing textile fibers (fibrous microplastics). A large amount of fibrous microplastics enters the environment during textile production and the first few washing cycles. Mechanical, thermal, chemical, and biological damage to textiles causes the generation of fibrous microplastics. Textile manufacturers, dyers and finishers, garment producers, distributors, or consumers contribute to this process. During the construction of textiles, multiple issues need to be addressed simultaneously. They are related to the optimization of technological processes and the construction and functionalization of fiber structures, considering ecological requirements, including suppressing the formation of fibrous microplastics. This research is focused on the specification of reasons for the generation of fibrous microplastics during textile production. The influence of the structure of fibers, abrasive deformations, and surface structure of fabrics on the generation of fibrous microplastics is discussed. The release of fibrous microplastics during washing is mentioned as well.
... Bacteria used in wastewater treatment are preferred for their detoxification properties. The biofilm of genetically modified P. aeruginosa has been shown to accumulate microplastics within 24 hours, indicating its potential for cleaning microplastics from environments such as wastewater and oceans (Liu et al., 2021). Additionally, Acinetobacter sp. and Scedosporium spp. ...
Conference Paper
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This review examines the structure and function of biofilms formed by microorganisms in various environments, as well as the advantages and disadvantages associated with these biofilms. Over an extended period of years, bacteria were considered to be planktonic (i.e., suspended or free-floating cells) and non-social organisms. Contrary to this view, bacteria in natural environments produce an extracellular matrix and form biofilm structures. These biofilms enable bacteria to establish symbiotic relationships within their own species and with other bacterial species, resulting in a resilient life form capable of withstanding environmental stresses, antibiotics, and host immune responses. Biofilms are characterized by structures that exhibit varying phenotypes in relation to growth rates and genetic expression, influenced by adhesion to interfaces, other cells, or substrates, and embedding within the extracellular polymeric matrix. The matrix, composed of various types of biopolymers produced by biofilm cells, serves multiple functions that significantly contribute to the biofilm lifestyle. It forms the structural skeleton of the biofilm, responsible for surface adhesion and cohesion. The extracellular polymeric substance (EPS) plays a critical role in stabilizing the biofilm by enhancing cohesive forces between cells. EPS immobilizes biofilm cells, which remain in close proximity, facilitating cell-cell communication and cooperative interactions. A comprehensive examination of biofilm characteristics will elucidate the complexities of these microorganism communities associated with surfaces. This review offers a thorough summary of the current literature.
... Researchers created a bacterial bio lm with a "capturerelease mechanism" as a proof of concept. This mechanism allows exopolysaccharide (EPS) to bioaggregate microplastics for simpler isolation and then releases the trapped microplastics through an inducible bio lm dispersal mechanism for the recovery of resources later (Liu et al. 2021). There is growing evidence that the interactions between bio lm and microplastic might alter the physical properties of the particles, hence affecting the fate and effects of microplastics. ...
Chapter
Plastic with a size of less than 5 mm in all dimensions has been considered microplastic. Microplastic occurs in the soil, river water, seawater, sludge, and effluent discharges due to anthropogenic activities. Microplastics and pharmaceutical medications have been reported to have combined actions in wastewater where microplastics serve as adsorbents for the pharmaceuticals. Polyamide, polyethylene, polystyrene, and polyvinylchloride microplastics have been reported in wastewater with adsorbent properties. Interaction between drugs and microplastics imposes ecological threat due to the persistence of the pollutants. For the removal of pharmaceuticals from the environment, some measures are required to desorb them from microplastic. This chapter gives insights into the role of microplastics as a vector for pharmaceutical drugs. This chapter summarizes the occurrence and fate of microplastics along with the sustainable technologies for the removal of microplastics from industrial wastewater.
... Environmental factors such as temperature, pH, humidity, salinity, and material properties determine the ability of microorganisms to adhere and form a biofilm. Liu et al. [36] developed an innovative method of microplastic biodegradation involving the creation of a bacterial biofilm based on the 'trap and release' mechanism. Extracellular polymeric substances (EPSs) are sticky colloidal substances produced by biofilms that capture microplastics and bioaggregate particles that are then released in a form suitable for further recycling and processing. ...
Article
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Abstract: The threat posed by microplastics has become one of the world’s most serious problems. Recent reports indicate that the presence of microplastics has been documented not only in coastal areas and beaches, but also in water reservoirs, from which they enter the bodies of aquatic animals and humans. Microplastics can also bioaccumulate contaminants that lead to serious damage to aquatic ecosystems. The lack of comprehensive data makes it challenging to ascertain the potential consequences of acute and chronic exposure, particularly for future generations. It is crucial to acknowledge that there is still a substantial need for rapid and effective techniques to identify microplastic particles for precise evaluation. Additionally, implementing legal regulations, limiting plastic production, and developing biodegradation methods are promising solutions, the implementation of which could limit the spread of toxic microplastics.
... However, it has been discovered that these microplastics allow for the formation of biofilms, which increases the coagulation and flocculation of these structures, facilitating their elimination [67]. Consequently, methods have been developed to trap microplastics using biofilms, as in the case of Liu and collaborators, who developed a method to capture and release microplastics as needed using wild-type and modified strains of P. aeruginosa [68]. Therefore, the search for new molecules capable of stimulating the formation of biofilms as a method to reduce microplastic pollution is part of the challenge [69]. ...
Article
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Polyphenols from agro-food waste represent a valuable source of bioactive molecules that can be recovered to be used for their functional properties. Another option is to use them as starting material to generate molecules with new and better properties through semi-synthesis. A proanthocyanidin-rich (PACs) extract from avocado peels was used to prepare several semi-synthetic derivatives of epicatechin by acid cleavage in the presence of phenol and thiol nucleophiles. The adducts formed by this reaction were successfully purified using one-step centrifugal partition chromatography (CPC) and identified by chromatographic and spectroscopic methods. The nine derivatives showed a concentration-dependent free radical scavenging activity in the DPPH assay. All compounds were also tested against a panel of pathogenic bacterial strains formed by Listeria monocytogenes (ATCC 7644 and 19115), Staphylococcus aureus (ATCC 9144), Escherichia coli (ATCC 11775 and 25922), and Salmonella enterica (ATCC 13076). In addition, adducts were tested against two no-pathogenic strains, Limosilactobacillus fermentum UCO-979C and Lacticaseibacillus rhamnosus UCO-25A. Overall, thiol-derived adducts displayed antimicrobial properties and, in some specific cases, inhibited biofilm formation, particularly in Listeria monocytogenes (ATCC 7644). Interestingly, phenolic adducts were inactive against all the strains and could not inhibit its biofilm formation. Moreover, depending on the structure, in specific cases, biofilm formation was strongly promoted. These findings contribute to demonstrating that CPC is a powerful tool to isolate new semi-synthetic molecules using avocado peels as starting material for PACc extraction. These compounds represent new lead molecules with antioxidant and antimicrobial activity.
... Genetic engineering approaches have also been applied in biofilm engineering to enhance the accumulation of MP molecules within it. In this direction, Pseudomonas aeruginosa was modified by the deletion of the wspF methylesterase gene to boost the synthesis of exopolymeric substances for improved binding of PVC molecules [181]. In another study, PET biodegradation was enhanced by cloning the gene encoding the polyester hydrolase enzyme responsible for PET degradation from Pseudomonas aestusnigri to E. coli [182]. ...
... The wspF gene was removed, enhancing its ability to remove MPs. The yhjH gene, inserted into the bacterium, reduced biofilm formation, allowing for effective microplastic scavengers for aquatic remediation (Liu et al. 2021). Genetic engineering techniques like recombinant DNA and gene cloning enhance bacteria's biodegradation of heavy metals and hydrocarbons, but developing plastic-breaking strains has received limited attention . ...
Article
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Micro- plastics (MPs) pose significant global threats, requiring an environment-friendly mode of decomposition. Microbial-mediated biodegradation and biodeterioration of micro-plastics (MPs) have been widely known for their cost-effectiveness, and environment-friendly techniques for removing MPs. MPs resistance to various biocidal microbes has also been reported by various studies. The biocidal resistance degree of biodegradability and/or microbiological susceptibility of MPs can be determined by defacement, structural deformation, erosion, degree of plasticizer degradation, metabolization, and/or solubilization of MPs. The degradation of microplastics involves microbial organisms like bacteria, mold, yeast, algae, and associated enzymes. Analytical and microbiological techniques monitor microplastic biodegradation, but no microbial organism can eliminate microplastics. MPs can pose environmental risks to aquatic and human life. Micro-plastic biodegradation involves fragmentation, assimilation, and mineralization, influenced by abiotic and biotic factors. Environmental factors and pre-treatment agents can naturally degrade large polymers or induce bio-fragmentation, which may impact their efficiency. A clear understanding of MPs pollution and the microbial degradation process is crucial for mitigating its effects. The study aimed to identify deteriogenic microorganism species that contribute to the biodegradation of micro-plastics (MPs). This knowledge is crucial for designing novel biodeterioration and biodegradation formulations, both lab-scale and industrial, that exhibit MPs-cidal actions, potentially predicting MPs-free aquatic and atmospheric environments. The study emphasizes the urgent need for global cooperation, research advancements, and public involvement to reduce micro-plastic contamination through policy proposals and improved waste management practices. Graphical abstract
... Yet, the efficacy of MPs removal can differ significantly depending on the treatment method and the specific type of plant, as illustrated in Fig. 7. Identifying the factors contributing to these variations and optimising treatment processes is crucial for enhancing MPs removal and reducing environmental contamination. Bilgin et al., 2020;Talvitie et al., 2017;Perren et al., 2018;Novotna et al., 2019;Xue et al., 2021;Prokopova et al., 2021;Ma et al., 2019;Pivokonsky et al., 2018;Dalmau-Soler et al., 2021;Wang et al., 2020;Sarkar et al., 2021;Risch and Adlhart, 2021;Sun et al., 2020;Sun et al., 2021a;Wang et al., 2021b;Yuan et al., 2020;Liang et al., 2019;Yogarathinam et al., 2022;Kuoppamäki et al., 2021;Wang et al., 2022;Chen et al., 2022;Rius-Ayra and Llorca-Isern, 2021;Zhou et al., 2021;Cunha et al., 2019;Cunha et al., 2020b;Faria et al., 2022;Liu et al., 2021b;Lengar et al., 2021. WWTPs primarily focus on primary and secondary treatments to eliminate MPs. ...
... In humans, the microbiota in the organs and tissues play important roles in the normal functioning of human cells. Biofilms can also be engineered to perform productive tasks, such as bioremediation of pollutants (6)(7)(8) or prevention of pathogen colonization. However, biofilms can be harmful to humans and the functioning of society. ...
... Polystyrene is used extensively in packaging, disposable plates, cups, trays, containers etc, whereas polyethylene is the major component of wrapping film, disposable bags, bottles, toys, etc (Achilias et al., 2007;Khemani, 1997). Unlike other large pollutants, microplastics are extremely difficult to remove from water bodies due to their smaller size (< 5 mm) and low densities (Liu et al., 2021;Lv et al., 2021;Vivekanand et al., 2021). They can persist in the water column for a prolonged duration and interact with biomolecules and toxicants present in the water (Prokić et al., 2019;Sárria et al., 2022). ...
... 7. Modern biotechnology techniques to accelerate the breakdown of microplastics 7.1 Genetic engineering methods Genetic alterations have been introduced to encourage the bacterial biofilm's ability to trap polyvinyl chloride (Liu et al., 2021). By genetically modifying Pseudomonas aeruginosa and removing the wspF gene, it has been made more capable of accumulating microplastics in its biofilm by increasing the production of sticky exopolymeric compounds. ...
Article
Recent studies on plastic pollution have shown that microscopic plastic particles or microplastics are ubiquitous. Both abiotic and biotic components are affected by microplastics. There are several ways to get rid of microplastics, that include recycling, landfilling, incineration, and biodegradation. Biodegradation is still a widely used remediation technology due to its significant economic and environmental benefits. One or more bio-cultures, such as bacteria, mould, yeast, and algae, can be used for biodegradation. In this review, we look through the contributions of microorganisms in biodegradation and other biotechnological techniques to speed up the process.
... Contaminants accumulated in plastic particles can be released into the aquatic environment through diffusion towards a low concentration gradient when plastic reaches an uncontaminated water (Bakir et al., 2014;Souza et al., 2017;Yao et al., 2022). Pathogens living on the surface can come out from that place to spread when the habitat is not enough and the population exceeds the capacity of the plastic capacity (Liu et al., 2021b). These released contaminants and microbes are further suspended, degraded, settled, or consumed by organisms . ...
Article
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To date, previous studies have reported the adverse effects of microplastics (MPs) and nanoplastics (NPs) on both freshwater and marine organisms. However, the information on MPs' and NPs' effects on shrimp species is scarce. In addition, the factors influencing the distribution of these particles in aquatic systems have been explained, yet the mechanisms behind MPs and NPs distribution and consumption, specifically to crustaceans and shrimp, have not been elucidated in detail. The effects of MPs and NPs as well as plastic-carried contaminants and pathogens on shrimp are critical to shrimp production and subsequent human consumption. Recent findings are required to review and discuss to open up new avenues for emerging Shrimp and crustacean research for sustainability. This review summarizes the distribution and fate of MPs and NPs along with contaminants and pathogens and identifies potential risks to shrimp health. The transport of MPs and NPs is influenced by their plastic properties, hydrodynamics, and water properties. Additionally, the fate of these particles on a plastic surface (plastisphere) is regulated by contaminant properties. Pathogens thriving on plastic surfaces and contaminants adsorbed can reach aquatic organisms directly with plastic particles or indirectly after release to an aquatic environment. MPs and NPs can be absorbed by shrimp through their gills and mouth and accumulate in their internal organs. Innate immunity influenced the degree of survival rate, tissue damage, alteration of gut microbiota, and increased oxidative stress caused by MPs and NPs accumulation. The studies on the effects of MPs and NPs are still not sufficient to understand how these particles are absorbed from various parts of the shrimp body and the fate of these plastics inside the body.
... Generally, a bioreactor is any system that involves organisms or biochemically active substances sourced from organisms, which have been useful in the manufacturing of 3 biopharmaceuticals, chemicals, food, and food additives. In addition, significant progress has been made in the application of microbial bioreactors in the bioremediation of various environmental pollutants such as dyes [11,12], heavy metals [13], organic contaminants [14], petroleum hydrocarbons, and, to a lesser degree, microplastics [15]. ...
Chapter
Conventional methods of removing plastic waste cause adverse environmental effects, which have sparked a huge interest in microbes as environmentally friendly alternatives. Microbes play a vital role in the self-cleaning ability of our planet, acting as microreactors, and have evolved over time to keep up with the ever-changing flux of xenobiotics and contaminants including plastic waste. These mini bioreactors include actinomycetes, algae, bacteria, and fungi, which along with their enzymes, are the key players in the plastic degradation process. These microbial enzymes have been demonstrated to partially degrade recalcitrant fossil-based plastic polymers such as polypropylene, polyethylene, polyethylene terephthalate, polystyrene, and polyvinyl chloride. In addition, they have also been shown to significantly break down the less resistant biobased plastics such as polylactic acid, polyhydroxyalkanoates, poly-3-hydroxybutyrate, polyhydroxyvalerate, and polyhydroxyhexanoate. Consequently, this chapter will examine how microorganisms and their enzymes can be utilized as bioresource for plastic degradation. It delves into the general mechanism of microbial plastic degradation centered on biofragmentation, biodeterioration, mineralization, and assimilation. In addition to the basic conventional methods used to identify and isolate plastic-degrading microbes and their enzymes, advanced biochemical techniques are also discussed for improving the efficiency of these bioreactors, such as metagenomics, protein engineering, and recombinant technology. This chapter also identifies critical knowledge gaps and future research directions in the effective utilization of microbes as bioresources for plastic degradation.
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Microplastics (MP) contamination in food and water poses significant health risks. While microbes that form biofilm show potential for removing MP from the environment, no methods currently exist to eliminate these non-degradable MP from the human body. In this study, we propose using probiotics to adsorb and remove ingested MP within the gut. We conducted a comprehensive evaluation of 784 bacterial strains to assess their ability to adsorb 0.1 μm polystyrene particles using a high-throughput screening method. Among the tested strains, Lacticaseibacillus paracasei DT66 and Lactiplantibacillus plantarum DT88 exhibited optimal adsorption in vitro and were effective across various MP types. In an animal model, mice treated with these probiotics demonstrated a 34% increase in PS excretion rates and a 67% reduction in residual polystyrene (PS) particles within the intestine. Additionally, administration of Lactiplantibacillus plantarum DT88 mitigated PS-induced intestinal inflammation. Together, our findings demonstrate a novel probiotic strategy for addressing MP-associated health risks, emphasizing the potential of strain-specific probiotics to remove MP from the gut environment.
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The presence of microplastics (MPs) in human body parts has raised significant concerns due to their status as a major environmental pollutant. Despite existing methods for detecting and identifying MPs in human tissues, there is a lack of standardized techniques, compromising the comparability of data across studies. This review critically analyzes the current knowledge on MPs in human body parts, sources and potential exposure pathways. This study underscores the urgent need for standardized and validated techniques for accurate MP analysis and characterization in human tissues, addressing the methodological challenges in MP detection. The findings of this review indicate that humans are exposed to MPs potentially through several routes such as ingestion, inhalation and dermal contact. However, the exact routes for MPs entering the body remain unclear. It also examines the wide range of health impacts associated with MPs, such as oxidative stress, inflammatory responses, endocrine disruption, and potential genotoxicity. Nevertheless, the cellular and molecular mechanisms underlying these effects are still not well understood, especially when considering the diverse concentrations, shapes, and sizes of MPs. Therefore, further research is essential, particularly to enhance epidemiological studies that can robustly establish the link between MP exposure and health impacts in large populations. Advancing this knowledge will be crucial for developing effective strategies to safeguard both environmental and public health from the detrimental effects of MPs. Keywords: Emerging contaminants; Microplastic Detection; Human health; Toxicity; Bioaccumulation; Mitigation strategies
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Chapter
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Pollutants can exert numerous adverse impacts on both human health and the environment. To minimize pollutants and their effects, it is important to reduce emissions, practice proper waste management, and use cleaner technologies. Polluted environments can be cleaned using bioremediation, a more cost-effective and environmentally friendly method than traditional methods. Several bioremediation techniques are available, including biostimulation, which stimulates the growth of naturally occurring microorganisms, and bioaugmentation, which enhances natural biodegradation by adding specific microorganisms or enzymes to the contaminated environment. Chemicals, pesticides, petroleum hydrocarbons, heavy metals, and petroleum hydrocarbons have all been successfully cleaned up using bioremediation. The use of genetically engineered microbes (GEMs) for environmental remediation involves modifying microorganisms to degrade or remove pollutants from contaminated environments. Although GEMs show promise as a solution to environmental pollution, there are also concerns about their potential unintended consequences, such as the spread of modified genes to other organisms. To implement GEMs on a large scale, it is important to evaluate the potential risks and benefits thoroughly. Treatment with microbes is a less costly and more effective method of removing pollutants from polluted environments. This chapter discussed challenges in designing multi-functional genetic engineering microorganisms for simultaneous pollutant removal from soil contaminated by GEMs and recent advances in bioremediation techniques and approaches.
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Microplastics are micrometre-sized emerging pollutants produced by plastic fragmentation. They have been recently detected in most ecosystems, even in remote areas. Here, we review microplastics with emphasis on sources, occurrence, transport, detection methods, policies, toxicity, and management methods. In the transport section, we discuss sorption kinetics, layered microplastics, and influencing factors such as biofilm formation. Microplastic management can be done by adsorption, filtration, oxidation, and biodegradation. Microplastic interaction is influenced by temperature, pH, salinity, and dissolved organic matter.
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Microorganisms, which are present ubiquitously in the earth, play a very important role in maintaining any kind of an ecosystem and aquatic ecosystems are no exception from it. These ecosystems are often prone to pollution and contamination by toxic and heavy metals, excess of nutrients (eutrophication), pathogens, foreign species, etc. which needs to be abated to keep it healthy. Also, to maintain the balance of an ecosystem, the nutrients must be recirculated and support for survival of the living organisms is required. These tasks are done by the microbial interactions with the pollutants and other organisms by taking different forms like biofilms and aggregates by employing various mechanisms like bioremediation (plant–microbe interactions), co-metabolism, etc. The microbes also decay the organic compounds which are generally applied to the fields thereby regulating the organic carbon, carbon dioxide and oxygen flow in the system. The microbes are one of the sole players responsible for fixing and regenerating the key organic elements like carbon, nitrogen, sulphur and phosphorous and mobilising the cofactors and vitamins necessary for metabolism, growth, and development of biological units. They are crucial for sustaining the food chains and food webs and thus regulate the energy and material fluxes. Functionally, these microbes support the living part of aquatic ecosystem and keep up the water quality. As a result of the associated interactions, they receive substances and services essential for their own survival and development which will be reviewed further in this chapter.
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[EXTENDED ABSTRACT] Background and aim: Efficient removal of environmental pollutants in a sustainable and eco-friendly manner demands innovative approaches relying on sound science. Various physico-chemcial approaches have been put forward to alleviate the pollution problem but many of these have practical limitations due to high implementation costs, toxic by-product formation, and redistribution of pollutants in the environment. Biological and microbiological approaches, on the other hand, offer more economically-viable and environmentally sustainable alternatives to manage pollutants. Microorganisms have immense potential to remove pollutants or transform recalcitrant xenobiotics into less toxic chemical species. Recent paradigms in the science of biodegradation and recent developments in bioremediation technologies urge the utilization of microbial consortia to effectively remove a wide array of environmental pollutants instead of employing single microbial species. Periphyton—a complex, inter-connected, and biofilm-forming biological community of micro and macroorganisms inhabiting wetland ecosystems—has been shown to interact with various critical pollutants and contribute to their biodegradation. The paper aims to highlight the biological processes employed by the periphytic community to remove organic pollutants, pharmaceuticals, heavy metals, microplastics, and excess nutrients. The study also discusses periphytic biofilm formation and their response mechanisms to pollution. Methodology: The present paper reviews the related literature to compile comprehensively the most essential and recent understanding of the interaction between periphyton and environmental pollutants. The article also describes the mechanisms employed by the periphytic biofilm in pollutant removal, addresses common challenges in periphyton-based bioremediation, and outlines research gaps for future studies. These findings prove helpful in developing periphyton-derived bioremediation technologies. Findings: The periphytic community is an integral and dynamic component of the wetland ecosystem, responding quickly to external stimuli. The community’s structural composition and biochemical processes change according to the prevailing surrounding conditions and the presence of pollutants. Periphyton uses various mechanisms to adapt to pollution and enable biodegradation. The unique characteristics and processes in the periphyton biological community that make it a powerful biodegradation agent include functional redundancy, ectopic or co-metabolism, extracellular polymeric substances synthesis, and pollutant-induced community tolerance. Moreover, the three-dimensional shape, porous nature, and voids in biofilms’ structure enhance pollutants’ bioadsorption and accumulation within the biofilm, removing them from the external environment. As such, studies have confirmed the considerable capacity of periphytic biofilms to remove organic pollutants, pharmaceuticals, heavy metals, microplastics, and excess nutrients from the environment. Conclusion: Periphyton-based bioremediation represents an innovative approach to managing environmental pollution. Although periphytic biofilms interact dynamically with living and non-living agents in their exterior and can alleviate environmental pollution via biosorption, assimilation, and biodegradation processes, effective and sustainable utilization of periphyton in bioremediation technologies demands the scientific community’s awareness of current bottlenecks and research gaps. Most importantly, attention needs to be given to controlling the growth of periphytic biofilms in a given ecosystem, increasing biofilms colonization potential and successful establishment in a new ecosystem, creating functionally-enriched periphyton with enhanced capacity in removing target pollutants, and safe and eco-friendly post-bioremediation disposal or reuse of periphyton. [Full text is in the Persian Lanugage]
Conference Paper
Bioremediation presents an environmentally-friendly, economic, and sustainable approach for reclaiming contaminated sites. The present review introduces periphyton as a complex microbial community consisting of various groups of microorganisms with versatile capabilities in removing environmental pollutants such as organic pollutants, pharmaceuticals, heavy metals, and microplastics. The paper is based on the key findings of recent scientific research and shines a light on the bioremediation potential of periphyton by comparing it with other microorganisms. In addition, certain essential research gaps are outlined. This study proves helpful in developing innovative and efficient bioremediation technologies. [Full-text is in the Persian language]
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As nanoplastics and persistent organic pollutants are broadly distributed in aquatic ecosystems and pose a potential threat to ecosystem, most pertinent studies have focused on aquatic animals, while studies on freshwater plants have been rarely reported. Therefore, we analyzed the single and combined toxicological impacts of various concentrations of 80 nm polystyrene nanoplastics (PS-NPs) including 0.5, 5, 10, and 20 mg/L and polychlorinated biphenyl-52 (PCB-52, 2,2′,5,5′- tetrachlorobiphenyl) at 0.1 mg/L on the aquatic plant Spirodela polyrhiza (S. polyrhiza) after a 10-day hydroponic experiment. Laser confocal scanning microscopy (LCSM) showed the accumulation of PS-NPs mainly in the root surface and the lower epidermis of leaves, and the enrichment of PS-NPs was aggravated by the presence of PCB-52. PS-NPs at 10 mg/L and 20 mg/L alone or in combination with PCB-52 notably inhibited the growth of S. polyrhiza, reduced the synthesis of chlorophylls a and b, and increased the activities of superoxide dismutase (SOD) and peroxidase (POD) as well as malondialdehyde (MDA) levels, and induced osmotic imbalance (soluble protein and soluble sugar contents) (p < 0.05). However, a single treatment with low levels of PS-NPs had positive effects on the growth (0.5 mg/L) and photosynthetic systems (0.5, 5 mg/L) of S. polyrhiza, while co-exposure exacerbated the damaging impacts of PS-NPs on the antioxidant defense system of S. polyrhiza, which was more pronounced in the roots. Furthermore, correlation analysis revealed that plant growth parameters were positively correlated with chlorophyll a and b content and negatively correlated with soluble sugars, antioxidant enzymes, lipid peroxidation, and carotenoid content (p < 0.05). These results provide data to improve the understanding of the single and combined ecotoxicological effects of nanoplastics and polychlorinated biphenyls (PCBs) in aquatic plants and their application in phytoremediation measures.
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Background: Microbes have been implicated in atherosclerosis development and progression, but the impact of bacterial-based biofilms on fibrous plaque rupture remains poorly understood. Results: Here, we developed a comprehensive atherosclerotic model to reflect the progression of fibrous plaque under biofilm-induced inflammation (FP-I). High expressions of biofilm-specific biomarkers algD, pelA and pslB validated the presence of biofilms. Biofilm promotes the polarization of macrophages towards a pro-inflammatory (M1) phenotype, as demonstrated by an increase in M1 macrophage-specific marker CD80 expression in CD68+ macrophages. The increase in the number of intracellular lipid droplets (LDs) and foam cell percentage highlighted the potential role of biofilms on lipid synthesis or metabolic pathways in macrophage-derived foam cells. In addition, collagen I production by myofibroblasts associated with the fibrous cap was significantly reduced along with the promotion of apoptosis of myofibroblasts, indicating that biofilms affect the structural integrity of the fibrous cap and potentially undermine its strength. Conclusion: We validated the unique role of biofilm-based inflammation in exacerbating fibrous plaque damage in the FP-I model, increasing fibrous plaque instability and risk of thrombosis. Our results lay the foundation for mechanistic studies of the role of biofilms in fibrous plaques, allowing the evaluation of preclinical combination strategies for drug therapy. Statement of significance: A microsystem-based model was developed to reveal interactions in fibrous plaque during biofilm-induced inflammation (FP-I). Real-time assessment of biofilm formation and its role in fibrous plaque progression was achieved. The presence of biofilms enhanced the expression of pro-inflammatory (M1) specific marker CD80, lipid droplets, and foam cells and reduced anti-inflammatory (M2) specific marker CD206 expression. Fibrous plaque exposure to biofilm-based inflammation reduced collagen I expression and increased apoptosis marker Caspase-3 expression significantly. Overall, we demonstrate the unique role of biofilm-based inflammation in exacerbating fibrous plaque damage in the FP-I model, promoting fibrous plaque instability and enhanced thrombosis risk. Our findings lay the groundwork for mechanistic studies, facilitating the evaluation of preclinical drug combination strategies.
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Microbial communities that form surface-attached biofilms must release and disperse their constituent cells into the environment to colonize fresh sites for continued survival of their species. For pathogens, biofilm dispersal is crucial for microbial transmission from environmental reservoirs to hosts, cross-host transmission, and dissemination of infections across tissues within the host. However, research on biofilm dispersal and its consequences in colonization of fresh sites remain poorly understood. Bacterial cells can depart from biofilms via stimuli-induced dispersal or disassembly due to direct degradation of the biofilm matrix, but the complex heterogeneity of bacterial populations released from biofilms rendered their study difficult. Using a novel 3D-bacterial "biofilm-dispersal-then-recolonization" (BDR) microfluidic model, we demonstrated that Pseudomonas aeruginosa biofilms undergo distinct spatiotemporal dynamics during chemical-induced dispersal (CID) and enzymatic disassembly (EDA), with contrasting consequences in recolonization and disease dissemination. Active CID required bacteria to employ bdlA dispersal gene and flagella to depart from biofilms as single cells at consistent velocities but could not recolonize fresh surfaces. This prevented the disseminated bacteria cells from infecting lung spheroids and Caenorhabditis elegans in on-chip coculture experiments. In contrast, EDA by degradation of a major biofilm exopolysaccharide (Psl) released immotile aggregates at high initial velocities, enabling the bacteria to recolonize fresh surfaces and cause infections in the hosts efficiently. Hence, biofilm dispersal is more complex than previously thought, where bacterial populations adopting distinct behavior after biofilm departure may be the key to survival of bacterial species and dissemination of diseases.
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Microplastic (MP) and Nanoplastic (NP) contamination have become a critical ecological concern due to their persistent presence in every aspect of the ecosystem and their potentially harmful effects. The current approaches to eradicate these wastes by burning up and dumping adversely impact the environment, while recycling has its own challenges. As a result, applying degradation techniques to eliminate these recalcitrant polymers has been a focus of scientific investigation in the recent past. Biological, photocatalytic, electrocatalytic, and, recently, nanotechnologies have been studied to degrade these polymers. Nevertheless, it is hard to degrade MPs and NPs in the environment, and these degradation techniques are comparatively inefficient and require further development. The recent research focuses on the potential use of microbes to degrade MPs and NPs as a sustainable solution. Therefore, considering the recent advancements in this important research field, this review highlights the utilization of organisms and enzymes for the biodegradation of the MPs and NPs with their probable degradation mechanisms. This review provides insight into various microbial entities and their enzymes for the biodegradation of MPs. In addition, owing to the lack of research on the biodegradation of NPs, the perspective of applying these processes to NPs degradation has also been looked at. Finally, a critical evaluation of the recent development and perspective for future research to improve the effective removal of MPs and NPs in the environment through biodegradation is also discussed.
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Plastic, and its pollution of marine ecosystems, has emerged as a global concern. Among the several other sources, plastics from abandoned, lost, or discarded fishing gears (ALDFG), and ropes are considered the most dangerous for marine wildlife. In EU states, the management ALDFG is prioritized through a dedicated action plan owing to the hazardous nature of ALDFG and the increase in commercial fishing activity in EU waters. The action plan demands to close the loop of plastics from fishing to ensure sustainable resource management using strategies of the circular economy (CE). Commercial fishing is a crucial sector in Norway, generating 4000 tons of waste plastic annually from fishing gears and ropes. While recycling, landfilling, and incineration are the standard end-of-life management options, the recycling industry in the region is immature. The lack of recycling capacity and inadequate infrastructure results in exporting most of the recyclable fraction out of Norway for further processing. Although within the framework of CE, the transboundary export of waste for recycling misses the opportunity to create value out of waste within the region. Therefore, in the pursuit of CE strategies, it is essential to ensure regional sustainability. In this study, we assess the environmental, economic, and social impacts of landfilling, incinerating, and recycling of waste fishing gears in Norway. To represent the current state, we include two existing recycling scenarios for the assessment, namely, recycling (inland) and recycling (export). Based on qualitative and quantitative data from relevant stakeholders, we adapted multi-criteria decision analysis (MCDA) to rank the end-of-life (EOL) alternatives through their ability to sustainably manage 4000 tons of waste plastics from fishing gears in Norway. The ranking and insights from stakeholder interaction were used to ascertain potential barriers in realizing principles of CE and to further recognize opportunities for establishing circular business models in the region.
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Microplastics in aquatic environments provide novel habitats for surface-colonizing microorganisms. Given the continuing debate on whether substrate-specific properties or environmental factors prevail in shaping biofilm assemblages on microplastics, we examined the influence of substrate vs. spatial factors in the development of bacterial assemblages on polyethylene (PE), polystyrene (PS), wood, and seston and in the free-living fraction. Further, the selective colonization of microplastics by potential pathogens was investigated because among the bacterial species found in microplastic-associated biofilms are potentially pathogenic Vibrio spp. Due to their persistence and great dispersal potential, microplastics could act as vectors for these potential pathogens and for biofilm assemblages in general. Incubation experiments with these substrates were conducted for 7 days during a summer cruise along the eastern Baltic Sea coastline in waters covering a salinity gradient of 4.5–9 PSU. Bacterial assemblages were analyzed using 16S rRNA-gene amplicon sequencing, distance-based redundancy analyses, and the linear discriminant analysis effect size method to identify taxa that were significantly more abundant on the plastics. The results showed that the sample type was the most important factor structuring bacterial assemblages overall. Surface properties were less significant in differentiating attached biofilms on PE, PS, and wood; instead, environmental factors, mainly salinity, prevailed. A potential role for inorganic-nutrient limitations in surface-specific attachment was identified as well. Alphaproteobacteria (Sphingomonadaceae, Devosiaceae, and Rhodobacteraceae) and Gammaproteobacteria (Alteromonadaceae and Pseudomonas) were distinctive for the PE- and PS-associated biofilms. Vibrio was more abundant on the PE and PS biofilms than on seston, but its abundances were highest on wood and positively correlated with salinity. These results corroborate earlier findings that microplastics constitute a habitat for biofilm-forming microorganisms distinct from seston, but less from wood. In contrast to earlier reports of low Vibrio numbers on microplastics, these results also suggest that vibrios are early colonizers of surfaces in general. Spatial as well as temporal dynamics should therefore be considered when assessing the potential of microplastics to serve as vectors for bacterial assemblages and putative pathogens, as these parameters are major drivers of biofilm diversity.
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We report the entire process underlying the NicR2 regulatory mechanism from association between free NicR2 and two promoters to dissociation of the NicR2-promoter complex. NicR2 can bind to another promoter, Pspm , which controls expression of nicotine-degrading genes that are not controlled by the Phsp promoter. We identified specific nucleotides of the Pspm promoter responsible for NicR2 binding. HSP was further demonstrated as an antagonist, which prevents the binding of NicR2 to the Pspm and Phsp promoters, by locking NicR2 in the derepression conformation. The competition between NicR2 and RNA polymerase is essential to initiate transcription of nicotine-degrading genes. This study extends our understanding of molecular mechanisms in biodegradation of environmental pollutants and toxicants.
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Wastewater treatment plants serve to collect and treat wastes that are known to include microplastic (MP; synthetic polymer materials <5 mm in size) and other small anthropogenic litter as particles, fibers and microbeads. Here, we determined the microplastic loads and removal efficiencies of three wastewater treatment plants (WWTPs) with different treatment sizes, operations and service compositions discharging to Charleston Harbor, South Carolina, USA over the course of a year. Overall, we found that MP concentrations (counts per L) varied within a factor of 2.5 in influent and 4.8 in effluent at each WWTP, and that neither concentrations nor removal efficiencies demonstrated a seasonal trend. The largest wastewater treatment plant in the study, which also employed primary clarification, had the highest MP removal efficiency of 97.6 ± 1.2%. The other two smaller facilities had average removal efficiencies of 85.2 ± 6.0% and 85.5 ± 9.1%. We demonstrate through source modeling that microplastic fiber loads in influent were consistent with service area populations laundering textiles given previously published rates of microplastic generation in washing machines. Using measured WWTP flow rates and MP counts, we find a combined load of MPs leaving all three WWTPs with discharged effluent totaling 500–1000 million MPs per day. We estimate from this the emission of 0.34–0.68 g MP per capita per year in treated wastewater, which may only account for <0.1% of plastic debris input to this metropolitan area's surface waters on an annual mass basis when land-based (mis)managed plastic waste sources are also considered. However, the potential for sorption of chemicals present in wastewater to microplastics and their small size, which confers immediate bioaccessibility, may present unique toxicological risks for microplastics discharged from WWTPs.
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Although the ubiquitous bacterial secondary messenger cyclic diguanylate (c-di-GMP) has important cellular functions in a wide range of bacteria, its function in the model plant pathogen Pseudomonas syringae remains largely elusive. To this end, we overexpressed Escherichia coli diguanylate cyclase (YedQ) and phosphodiesterase (YhjH) in P. syringae, resulting in high and low in vivo levels of c-di- GMP, respectively. Via genome-wide RNA sequencing of these two strains, we found that c-di-GMP regulates (i) fliN, fliE, and flhA, which are associated with flagellar assembly; (ii) alg8 and alg44, which are related to the exopolysaccharide biosynthesis pathway; (iii) pvdE, pvdP, and pvsA, which are associated with the siderophore biosynthesis pathway; and (iv) sodA, which encodes a superoxide dismutase. In particular, we identified three promoters that are sensitive to elevated levels of c-di-GMP and inserted them into luciferase-based reporters that respond effectively to the c-di-GMP levels in P. syringae; these promoters could be useful in the measurement of in vivo levels of c-di-GMP in real time. Further phenotypic assays validated the RNA sequencing (RNA-seq) results and confirmed the effect on c-di-GMP-associated pathways, such as repressing the type III secretion system (T3SS) and motility while inducing biofilm production, siderophore production, and oxidative stress resistance. Taken together, these results demonstrate that c-di-GMP regulates the virulence and stress response in P. syringae, which suggests that tuning its level could be a new strategy to protect plants from attacks by this pathogen.
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Ocean plastic pollution has resulted in a substantial accumulation of microplastics in the marine environment. Today, this plastic litter is ubiquitous in the oceans, including even remote habitats such as deep-sea sediments and polar sea ice, and it is believed to pose a threat to ecosystem health. However, the concentration of microplastics in the surface layer of the oceans is considerably lower than expected, given the ongoing replenishment of microplastics and the tendency of many plastic types to float. It has been hypothesized that microplastics leave the upper ocean by aggregation and subsequent sedimentation. We tested this hypothesis by investigating the interactions of microplastics with marine biogenic particles collected in the southwestern Baltic Sea. Our laboratory experiments revealed a large potential of microplastics to rapidly coagulate with biogenic particles, which substantiates this hypothesis. Together with the biogenic particles, the microplastics efficiently formed pronounced aggregates within a few days. The aggregation of microplastics and biogenic particles was significantly accelerated by microbial biofilms that had formed on the plastic surfaces. We assume that the demonstrated aggregation behaviour facilitates the export of microplastics from the surface layer of the oceans and plays an important role in the redistribution of microplastics in the oceans.
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Significance Synthetic polymers are ubiquitous in the modern world but pose a global environmental problem. While plastics such as poly(ethylene terephthalate) (PET) are highly versatile, their resistance to natural degradation presents a serious, growing risk to fauna and flora, particularly in marine environments. Here, we have characterized the 3D structure of a newly discovered enzyme that can digest highly crystalline PET, the primary material used in the manufacture of single-use plastic beverage bottles, in some clothing, and in carpets. We engineer this enzyme for improved PET degradation capacity and further demonstrate that it can also degrade an important PET replacement, polyethylene-2,5-furandicarboxylate, providing new opportunities for biobased plastics recycling.
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Although plastic is ubiquitous in marine systems, our current knowledge of transport mechanisms is limited. Much of the plastic entering the ocean sinks; this is intuitively obvious for polymers such as polystyrene (PS), which have a greater density than seawater, but lower density polymers like polyethylene (PE) also occur in sediments. Biofouling can cause large plastic objects to sink, but this phenomenon has not been described for microplastics < 5 mm. We incubated PS and PE microplastic particles in estuarine and coastal waters to determine how biofouling changes their sinking behavior. Sinking velocities of PS increased 16% in estuarine water (salinity 9.8) and 81% in marine water (salinity 36) after 6 weeks of incubation. Thereafter sinking velocities decreased due to lower water temperatures and reduced light availability. Biofouling did not cause PE to sink during the 14 weeks of incubation in estuarine water, but PE started to sink after six weeks in coastal water when sufficiently colonized by blue mussels Mytilus edulis, and its velocity continued to increase until the end of the incubation period. Sinking velocities of these PE pellets were similar irrespective of salinity (10 vs. 36). Biofilm composition differed between estuarine and coastal stations, presumably accounting for differences in sinking behavior. We demonstrate that biofouling enhances microplastic deposition to marine sediments, and our findings should improve microplastic transport models.
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Plastics have outgrown most man-made materials and have long been under environmental scrutiny. However, robust global information, particularly about their end-of-life fate, is lacking. By identifying and synthesizing dispersed data on production, use, and end-of-life management of polymer resins, synthetic fibers, and additives, we present the first global analysis of all mass-produced plastics ever manufactured. We estimate that 8300 million metric tons (Mt) as of virgin plastics have been produced to date. As of 2015, approximately 6300 Mt of plastic waste had been generated, around 9% of which had been recycled, 12% was incinerated, and 79% was accumulated in landfills or the natural environment. If current production and waste management trends continue, roughly 12,000 Mt of plastic waste will be in landfills or in the natural environment by 2050.
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In the aquatic environment, microplastic (MP; <5 mm) is a cause of concern because of its persistence and potential adverse effects on biota. Studies of microlitter impacts are mostly based on virgin and spherical polymer particles as model MP. However, in pelagic and benthic environments, surfaces are always colonized by microorganisms forming so-called biofilms. The influence of such biofilms on the fate and potential effects of MP is not understood well. Here, we review the physical interactions of early microbial colonization on plastic surfaces and their reciprocal influence on the weathering processes and vertical transport as well as sorption and release of contaminants by MP. Possible ecological consequences of biofilm formation on MP, such as trophic transfer of MP particles and potential adverse effects of MP, are virtually unknown. However, evidence is accumulating that the biofilm−plastic interactions have the capacity to influence the fate and impacts of MP by modifying the physical properties of the particles. There is an urgent research need to better understand these interactions and increase the ecological relevance of current laboratory testing by simulating field conditions in which microbial life is a key driver of biogeochemical processes.
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Synthetic plastics, which are widely present in materials of everyday use, are ubiquitous and slow-degrading polymers in environmental wastes. Of special interest are the capabilities of microorganisms to accelerate their degradation. Members of the metabolically-diverse genus Pseudomonas are of particular interest due their capabilities to degrade and metabolize synthetic plastics. Pseudomonas species isolated from environmental matrices have been identified to degrade polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyurethane, polyethylene terephthalate, polyethylene succinate, polyethylene glycol, and polyvinyl alcohol at varying degrees of efficiency. Here we present a review of the current knowledge on the factors that control the ability of Pseudomonas spp. to process these different plastic polymers and their byproducts. These factors include cell surface attachment within biofilms, catalytic enzymes involved in oxidation or hydrolysis of the plastic polymer, metabolic pathways responsible for uptake and assimilation of plastic fragments, and chemical factors that are advantageous or inhibitory to the biodegradation process. We also highlight future research directions required in order to harness fully the capabilities of Pseudomonas spp. in bioremediation strategies towards eliminating plastic wastes.
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The host immune system offers a hostile environment with antimicrobials and reactive oxygen species (ROS) that are detrimental to bacterial pathogens, forcing them to adapt and evolve for survival. However, the contribution of oxidative stress to pathogen evolution remains elusive. Using an experimental evolution strategy, we show that exposure of the opportunistic pathogen Pseudomonas aeruginosa to sub-lethal hydrogen peroxide (H2O2) levels over 120 generations led to the emergence of pro-biofilm rough small colony variants (RSCVs), which could be abrogated by l-glutathione antioxidants. Comparative genomic analysis of the RSCVs revealed that mutations in the wspF gene, which encodes for a repressor of WspR diguanylate cyclase (DGC), were responsible for increased intracellular cyclic-di-GMP content and production of Psl exopolysaccharide. Psl provides the first line of defence against ROS and macrophages, ensuring the survival fitness of RSCVs over wild-type P. aeruginosa. Our study demonstrated that ROS is an essential driving force for the selection of pro-biofilm forming pathogenic variants. Understanding the fundamental mechanism of these genotypic and phenotypic adaptations will improve treatment strategies for combating chronic infections.
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Biofilms are surface-associated communities of microorganism embedded in extracellular matrix. Exopolysaccharide is a critical component in the extracellular matrix that maintains biofilm architecture and protects resident biofilm bacteria from antimicrobials and host immune attack. However, self-produced factors that target the matrix exopolysaccharides, are still poorly understood. Here, we show that PslG, a protein involved in the synthesis of a key biofilm matrix exopolysaccharide Psl in Pseudomonas aeruginosa, prevents biofilm formation and disassembles existing biofilms within minutes at nanomolar concentrations when supplied exogenously. The crystal structure of PslG indicates the typical features of an endoglycosidase. PslG mainly disrupts the Psl matrix to disperse bacteria from biofilms. PslG treatment markedly enhances biofilm sensitivity to antibiotics and macrophage cells, resulting in improved biofilm clearance in a mouse implant infection model. Furthermore, PslG shows biofilm inhibition and disassembly activity against a wide range of Pseudomonas species, indicating its great potential in combating biofilm-related complications.Cell Research advance online publication 27 November 2015; doi:10.1038/cr.2015.129.
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Stress response plays an important role on microbial adaptation under hostile environmental conditions. It is generally unclear how the signaling transduction pathway mediates a stress response in planktonic and biofilm modes of microbial communities simultaneously. Here, we showed that metalloid tellurite (TeO32–) exposure induced the intracellular content of the secondary messenger cyclic di-GMP (c-di-GMP) of Pseudomonas aeruginosa. Two diguanylate cyclases (DGCs), SadC and SiaD, were responsible for the increased intracellular content of c-di-GMP. Enhanced c-di-GMP levels by TeO32– further increased P. aeruginosa biofilm formation and resistance to TeO32–. P. aeruginosa ΔsadCΔsiaD and PAO1/plac-yhjH mutants with low intracellular c-di-GMP content were more sensitive to TeO32– exposure and had low relative fitness compared to the wild-type PAO1 planktonic and biofilm cultures exposed to TeO32–. Our study provided evidence that c-di-GMP level can play an important role in mediating stress response in microbial communities during both planktonic and biofilm modes of growth.
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The nucleotide signaling molecule bis-(3'-5')-cyclic dimeric guanosine monophosphate (c-di-GMP) plays an essential role in regulating microbial virulence and biofilm formation. C-di-GMP is synthesized by diguanylate cyclase (DGC) enzymes and degraded by phosphodiesterase (PDE) enzymes. One intrinsic feature of c-di-GMP signaling is the abundance of DGCs and PDEs encoded by many bacterial species. It is unclear whether the different DGCs or PDEs coordinately establish the c-di-GMP regulation or function independently of each other. Here, we provide evidence that multiple DGCs are involved in regulation of c-di-GMP on synthesis of the major iron siderophore pyoverdine in Pseudomonas aeruginosa. Constitutive expression of the WspG or YedQ DGC in P. aeruginosa is able to induce its pyoverdine synthesis. Induction of pyoverdine synthesis by high intracellular c-di-GMP depends on the synthesis of exopolysaccharides and another two DGCs, SiaD and SadC. SiaD was found to boost the c-di-GMP synthesis together with constitutively expressing YedQ. The exopolysaccharides and the SiaD DGC were found to modulate the expression of the RsmY/RsmZ ncRNAs. Induction of the RsmY/RsmZ ncRNAs might enhance the pyoverdine synthesis through SadC. Our study sheds light on a novel multiple-DGC-coordinated (MDC) c-di-GMP regulatory mechanism of bacteria. This article is protected by copyright. All rights reserved.
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Cyclic di-GMP (c-di-GMP) has emerged as an important intracellular signaling molecule, controlling the transitions between planktonic (free-living) and sessile lifestyles, biofilm formation, and virulence in a wide variety of microorganisms. The following protocol describes the extraction and quantification of c-di-GMP from Pseudomonas aeruginosa samples. We have made every effort to keep the protocol as general as possible to enable the procedure to be applicable for the analysis of c-di-GMP levels in various bacterial species. However, some modifications may be required for the analysis of c-di-GMP levels in other bacterial species.
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The bis-(3'-5')-cyclic dimeric guanosine monophosphate (c-di-GMP) is a ubiquitous second messenger that determines bacterial lifestyle between the planktonic and biofilm modes of life. Although the role of c-di-GMP signaling in biofilm development and dispersal has been extensively studied, how c-di-GMP signaling influences environmental bioprocess activities such as biodegradation remains unexplored. To elucidate the impacts of elevating c-di-GMP level on environmental bioprocesses, we constructed a Comamonas testosteroni strain constitutively expressing a c-di-GMP synthase YedQ from Escherichia coli and examined its capability in biofilm formation and biodegradation of 3-chloroaniline (3-CA). The high c-di-GMP strain exhibited an increased binding to Congo red dye, a decreased motility, and an enhanced biofilm formation capability. In planktonic cultures, the strain with an elevated c-di-GMP concentration and the wild type could degrade 3-CA comparably well. However, under batch growth conditions with a high surface to volume ratio, an elevated c-di-GMP concentration in C. testosteroni significantly increased the contribution of biofilms in 3-CA biodegradation. In continuous submerged biofilm reactors, C. testosteroni with an elevated c-di-GMP level exhibited an enhanced 3-CA biodegradation and a decreased cell detachment rate. Taken together, this study provides a novel strategy to enhance biofilm-based biodegradation of toxic xenobiotic compounds through manipulating bacterial c-di-GMP signaling.
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Bacteria assume distinct lifestyles during the planktonic and biofilm modes of growth. Increased levels of the intracellular messenger c-di-GMP determine the transition from planktonic to biofilm growth, while a reduction causes biofilm dispersal. It is generally assumed that cells dispersed from biofilms immediately go into the planktonic growth phase. Here we use single-nucleotide resolution transcriptomic analysis to show that the physiology of dispersed cells from Pseudomonas aeruginosa biofilms is highly different from those of planktonic and biofilm cells. In dispersed cells, the expression of the small regulatory RNAs RsmY and RsmZ is downregulated, whereas secretion genes are induced. Dispersed cells are highly virulent against macrophages and Caenorhabditis elegans compared with planktonic cells. In addition, they are highly sensitive towards iron stress, and the combination of a biofilm-dispersing agent, an iron chelator and tobramycin efficiently reduces the survival of the dispersed cells.
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