In offshore production facilities, large amounts of deaerated seawater are continuously injected to maintain pressure in oil reservoirs and equivalent volumes of fluids, composed of an oil/gas, and water mixture are produced. This process, brewing billions of liters of biphasic fluids particularly rich in microorganisms, goes through complex steel pipeline networks that are particularly prone to biofilm formation. Consequently, offshore facilities are frequently victims of severe microbiologically influenced corrosion. Understanding of microbiologically influenced corrosion is constantly growing. In the laboratory, the inventory of potentially corrosive microorganisms is increasing and microbial biochemical and bioelectrical processes are now recognized to be involved in corrosion. However, understanding of corrosive multispecies biofilms and the complex metabolic processes associated with corrosion remains a considerable challenge as simple laboratory biofilms comprising pure or defined mixed cultures poorly represent the complexity of in situ biofilms. Complementary, antagonistic, and parallel microbial pathways occur within the complex microbial and inorganic matrix of the biofilms which can lead to high corrosion rates. This mini-review explores models of microbiologically influenced corrosion and places them in the context of the multispecies biofilms observed in situ. Consequences of mitigation strategies on biofilm corrosiveness and dispersal are also discussed.

The vast translucent oceans are teeming with microscopic life that drives significant life processes and elemental cycling on Earth. Yet how climate change will affect the functioning of this microbiome is not well understood. Moran reviews progress and the transformative discoveries made recently in marine microbiology that have led environmental, plant, animal, and even human microbiome research.

Microbial biofilms can be both cause and cure to a range of emerging societal problems including antimicrobial tolerance, water sanitation, water scarcity and pollution. The identities of extracellular polymeric substances (EPS) responsible for the establishment and function of biofilms are poorly understood. The lack of information on the chemical and physical identities of EPS limits the potential to rationally engineer biofilm processes, and impedes progress within the water and wastewater sector towards a circular economy and resource recovery. Here, a multidisciplinary roadmap for addressing this EPS identity crisis is proposed. This involves improved EPS extraction and characterization methodologies, cross-referencing between model biofilms and full-scale biofilm systems, and functional description of isolated EPS with in situ techniques (e.g. microscopy) coupled with genomics, proteomics and glycomics. The current extraction and spectrophotometric characterization methods, often based on the principle not to compromise the integrity of the microbial cells, should be critically assessed, and more comprehensive methods for recovery and characterization of EPS need to be developed.Copyright © 2018 Elsevier Ltd. All rights reserved.

Sulphate-reducing bacteria (SRB) are anaerobic microorganisms that use sulphate as a terminal electron acceptor in, for example, the degradation of organic compounds. They are ubiquitous in anoxic habitats, where they have an important role in both the sulphur and carbon cycles. SRB can cause a serious problem for industries, such as the offshore oil industry, because of the production of sulphide, which is highly reactive, corrosive and toxic. However, these organisms can also be beneficial by removing sulphate and heavy metals from waste streams. Although SRB have been studied for more than a century, it is only with the recent emergence of new molecular biological and genomic techniques that we have begun to obtain detailed information on their way of life.

Microbiologically influenced corrosion (MIC) is a major concern in a wide range of industries, with claims that it contributes 20% of the total annual corrosion cost. The focus of this present work is to review critically the most recent proposals for MIC mechanisms, with particular emphasis on whether or not these make sense in terms of their electrochemistry. It is determined that, despite the long history of investigating MIC, we are still a long way from really understanding its fundamental mechanisms, especially in relation to non-sulphate reducing bacterial (SRB) anaerobes. Nevertheless, we do know that both the cathodic polarization theory and direct electron transfer from the metal into the cell are incorrect. Electrically conducting pili also do not appear to play a role in direct electron transfer, although these could still play a role in aiding the mass transport of redox mediators. However, it is not clear if the microorganisms are just altering the local chemistry or if they are participating directly in the electrochemical corrosion process, albeit via the generation of redox mediators. The review finishes with suggestions on what needs to be done to further our understanding of MIC.

Over 258 Mt of solid waste are generated annually in Europe, a large fraction of which is biowaste. Sewage sludge is another major waste fraction. In this study, biowaste and sewage sludge were co-digested in an anaerobic digestion reactor (30% and 70% of total wet weight, respectively). The purpose was to investigate the biogas production and methanogenic archaeal community composition in the anaerobic digestion reactor under meso- (35-37 °C) and thermophilic (55-57 °C) processes and an increasing organic loading rate (OLR, 1-10 kg VS m(-3) d(-1)), and also to find a feasible compromise between waste treatment capacity and biogas production without causing process instability. In summary, more biogas was produced with all OLRs by the thermophilic process. Both processes showed a limited diversity of the methanogenic archaeal community which was dominated by Methanobacteriales and Methanosarcinales (e.g. Methanosarcina) in both meso- and thermophilic processes. Methanothermobacter was detected as an additional dominant genus in the thermophilic process. In addition to operating temperatures, the OLRs, the acetate concentration, and the presence of key substrates like propionate also affected the methanogenic archaeal community composition. A bacterial cell count 6.25 times higher than archaeal cell count was observed throughout the thermophilic process, while the cell count ratio varied between 0.2 and 8.5 in the mesophilic process. This suggests that the thermophilic process is more stable, but also that the relative abundance between bacteria and archaea can vary without seriously affecting biogas production. Copyright © 2014 Elsevier Ltd. All rights reserved.

Molecular structures and sequences are generally more revealing of evolutionary relationships than are classical phenotypes (particularly so among microorganisms). Consequently, the basis for the definition of taxa has progressively shifted from the organismal to the cellular to the molecular level. Molecular comparisons show that life on this planet divides into three primary groupings, commonly known as the eubacteria, the archaebacteria, and the eukaryotes. The three are very dissimilar, the differences that separate them being of a more profound nature than the differences that separate typical kingdoms, such as animals and plants. Unfortunately, neither of the conventionally accepted views of the natural relationships among living systems--i.e., the five-kingdom taxonomy or the eukaryote-prokaryote dichotomy--reflects this primary tripartite division of the living world. To remedy this situation we propose that a formal system of organisms be established in which above the level of kingdom there exists a new taxon called a "domain." Life on this planet would then be seen as comprising three domains, the Bacteria, the Archaea, and the Eucarya, each containing two or more kingdoms. (The Eucarya, for example, contain Animalia, Plantae, Fungi, and a number of others yet to be defined). Although taxonomic structure within the Bacteria and Eucarya is not treated herein, Archaea is formally subdivided into the two kingdoms Euryarchaeota (encompassing the methanogens and their phenotypically diverse relatives) and Crenarchaeota (comprising the relatively tight clustering of extremely thermophilic archaebacteria, whose general phenotype appears to resemble most the ancestral phenotype of the Archaea.

Natural and artificial substrata immersed in the marine environment are typically colonized by microorganisms, which may moderate the settlement/recruitment of algal spores and invertebrate larvae of macrofouling organisms. This mini-review summarizes the major interactions occurring between microbial biofilms and marine fouling algae, including their effects on the settlement, growth and morphology of the adult plants. The roles of chemical compounds that are produced by both bacteria and algae and which drive the interactions are reviewed. The possibility of using such bioactive compounds to control macrofouling will be discussed.

Interrelations between epiphytic bacteria and macroalgae are multifaceted and complicated, though little is known about the community structure, interaction and functions of those epiphytic bacteria. This study comprehensively characterized the epiphytic bacterial communities associated with eight different common seaweeds collected from a rocky intertidal zone on the Indian Ocean at Cape Vidal, South Africa. High-throughput sequencing analyses indicated that seaweed-associated bacterial communities were dominated by the phyla Proteobacteria, Bacteroidetes, Firmicutes, Cyanobacteria, Planctomycetes, Actinobacteria and Verrucomicrobia. Energy-dispersive X-ray (EDX) analysis showed the presence of elemental composition in the surface of examined seaweeds, in varying concentrations. Cluster analysis showed that bacterial communities of brown seaweeds (SW2 and SW4) were closely resembled those of green seaweeds (SW1) and red seaweeds (SW7) while those of brown seaweeds formed a separate branch. Predicted functional capabilities of epiphytic bacteria using PICRUSt analysis revealed abundance of genes related to metabolic and biosynthetic activities. Further important identified functional interactions included genes for bacterial chemotaxis, which could be responsible for the observed association and network of elemental-microbes interaction. The study concludes that the diversity of epiphytic bacteria on seaweed surfaces is greatly influenced by algal organic exudates as well as elemental deposits on their surfaces, which triggers chemotaxis responses from epiphytic bacteria with the requisite genes to metabolise those substrates.

In the marine environment, microbiologically influenced corrosion (MIC) is a major problematic issue, which leads to severe damage to metals and alloys. The prerequisite to mitigate this worldwide problem is to investigate the mechanisms of marine-corroding microbes. Therefore, the corrosion behavior of 316L stainless steel in the presence of marine was investigated by means of electrochemical measurements and surface analysis. The results revealed that is capable of forming a dense and thick biofilm on the surfaces of 316L SS coupons after 7 days of incubation, which reached about a thickness of 40.4 μm. According to electrochemical results, the biofilm also induced the corrosion of 316L SS coupons. The accelerated corrosion of 316L SS coupons was in the form of pits, which was formed underneath the biofilms. The largest pit depth after 14 days of incubation time reached 9.8 μm, which was 6.7 times higher than the one immersed in abiotic medium (1.45 μm). This is the first study demonstrating the MIC of 316L SS due to the biofilm.

In the continuation of our research on seaweeds, crude extracts of 21 brown algae collected from the south coast of England and the west coast of Ireland were screened for in vitro trypanocidal, leishmanicidal and antimycobacterial activities. Mammalian stages of a small set of parasitic protozoa; i.e. Trypanosoma brucei rhodesiense, T. cruzi and Leishmania donovani, and the tubercle bacillus Mycobacterium tuberculosis were used as test organisms. The extracts were also evaluated for selectivity by testing on a mammalian cell line (L6 cells). Only four extracts were moderately active against T. cruzi, whereas all algal extracts showed significant activity against T. brucei rhodesiense, with Halidrys siliquosa and Bifurcaria bifurcata (Sargassaceae) being the most potent (IC50 values 1.2 and 1.9 μg/mL). All algal extracts also displayed leishmanicidal activity, with H. siliquosa and B. bifurcata again being the most active (IC50s 6.4 and 8.6 μg/mL). When tested against M. tuberculosis, only the B. bifurcata extract was found to have some antitubercular potential (MIC value 64.0 μg/mL). Only three seaweed extracts, i.e. H. siliquosa, B. bifurcata and Cystoseira tamariscifolia showed some cytotoxicity. To our knowledge, this is the first study on the antiprotozoal and antimycobacterial activity of brown algae from British and Irish waters.Copyright © 2010 John Wiley & Sons, Ltd.

Aerobic glucose metabolism by Pseudomonas aeruginosa in steady-state biofilms at various substrate loading rates and reactor dilution rates was investigated. Variables monitored were substrate (glucose), biofilm cellular density, biofilm extracellular polymeric substance (EPS) density, and suspended cellular and EPS concentrations. A mathematical model developed to describe the system was compared to experimental data. Intrinsic yield and rate coefficients included in the model were obtained from suspended continuous culture studies of glucose metabolism by P. aeruginosa. Experimental data compared well with the mathematical model, suggesting that P. aeruginosa does not behave differently in steady-state biofilm cultures, where diffusional resistance is negligible, than in suspended cultures. This implies that kinetic and stoichiometric coefficients for P. aeruginosa derived in suspended continuous culture can be used to describe steady-state biofilm processes.

One of the key elements in the establishment and maintenance of the biofilm structure and properties is the extracellular matrix. The extracellular matrix is composed of water and extracellular polymeric substances (EPS): primarily polysaccharides, proteins and DNA. Characterization of the matrix requires component identification, as well as determination of the relative concentration of EPS constituents, including their physicochemical properties and descriptions of their interactions. Several types of experimental approaches with varying degrees of destructiveness can be utilized for this characterization. The analysis of biofilm by infrared spectroscopy gives information about the chemical content of the matrix and the proportions of different EPS. The sensitivity of a biofilm to hydrolytic enzymes targeting different EPS gives insight into the composition of the matrix and the involvement of matrix components in the integrity of the structure. Using both chemical and physical treatments, extraction and purification of EPS from the biofilm also provides a means of determining matrix composition. Purified and/or artificial EPS can be used to obtain artificial matrices and to study their properties. Using examples from the literature, this review will illustrate selected technologies useful in the study of EPS that provide a better understanding of the structure-function relationships in extracellular matrix, and thus the structure-function relationships of the biofilm phenotype.

The presence and the transformations of organic fractions within biofilms are not usually included in biofilm models, mainly owing to the lack of knowledge of the important processes, the stoichiometry and the kinetics. A conceptual biofilm model taking into account microbial physiology with regard to production of extracellular polymers and their transformation within the biofilm is suggested. The suggested components in the biofilm are the cell biomass and the various extracellular polymeric substances (EPS), such as polysaccharides, protein, humic substances and nucleic acids. In addition, environmental factors that influence the microbial exopolymer production and composition are taken into account. The suggested conceptual model can be helpful in structuring the design and evaluation of biofilm experiments focusing on biofilm structure and properties.

Microalgae have been studied as natural resources for a number of applications, most particularly food, animal feed, biofuels, pharmaceuticals, and nutraceuticals. In addition to the intracellular compounds of interest, microalgae can also excrete various extracellular polymeric substances (EPS) into their immediate living environment during their life cycle to form a hydrated biofilm matrix. These microalgal EPS mainly consist of polysaccharides, proteins, nucleic acids and lipids. Most notably, EPS retain their stable matrix structure and form a 3-D polymer network for cells to interact with each other, and mediate their adhesion to surfaces. EPS also play a role as extracellular energy and carbon sinks. They are also abundant source of structurally and compositionally diverse biopolymers which possess unique bioactivities for special high-value applications, specifically as antivirals, antitumor agents, antioxidants, anticoagulants and anti-inflammatories. Their superior rheological properties also make microalgal EPS particularly useful in mechanical engineering (e.g., biolubricants and drag reducers) and food science/engineering (e.g., thickener and preservatives) applications. The chemical composition and structure of EPS appear to correlate with their applications, but the fundamentals of such relationship are not well understood. This article summarizes previous research on microalgal EPS derived from green algae, diatoms and red algae, including compositions/functions/structure, production, and potential applications. The importance of exopolysaccharides and EPS proteins, with their particular metabolic characteristics, are also described because of their potential high-value applications. This review concludes with potential future research areas of microalgal EPS.Copyright © 2016 Elsevier Inc. All rights reserved.

Microbial biofilms and most eukaryotic tissues consist of cells embedded in a three-dimensional extracellular matrix. This matrix serves as a scaffold for cell adhesion and a dynamic milieu that provides varying chemical and physical signals to the cells. Besides a vast array of specific molecular components, an extracellular matrix can provide locally heterogeneous microenvironments differing in porosity/diffusion, stiffness, pH, oxygen and metabolites or nutrient levels. Mechanisms of matrix formation, mechanosensing, matrix remodeling, and modulation of cell-cell or cell-matrix interactions and dispersal are being revealed. This perspective article aims to identify such concepts from the fields of biofilm or eukaryotic matrix biology relevant to the other field to help stimulate new questions, approaches, and insights.Copyright © 2016 Elsevier Ltd. All rights reserved.

Microorganisms can utilize an extensive assortment of carbon and nitrogen sources as well as various added nutrients ranging from simple to complex. Depending on the microbe and the metabolic pathway they undergo, these nutrients are efficiently converted into complex and diverse biopolymers with varied physico-chemical properties. Exopolysaccharides (EPS) are biopolymers that primarily contain- carbohydrates. The extensively studied EPS producing bacteria include Leuconostoc mesenteroides, Xanthomonas campestris, Acinetobacter calcoaceticus, Lactobacillus sp. and Alkaligenes sp. However, some prominent fungal exopolysaccharides produced by Aspergillus niger, Lentinula edodes, Fusarium solani, Botryosphaeria rhodina, Coriolus versicolor have also been put to commercial use. While the microbes may vary substantially in their physiology, the production of EPS depends largely on the optimization of the growth by varying various parameters influencing growth and the meticulous designing of its production media. EPS acts as an invaluable asset for the producing microbe by providing manifold benefits including but not restricted to: protection against- desiccation, starvation, phagocytosis, UV radiation, environmental stress and water retention. Being eco-friendly and biodegradable, major microbial EPS such as; dextran, xanthan, alginate, hyaluronan, pullulan, chitosan and lentinam have found numerous vital applications in pharmaceutical, agriculture, food and cosmetics industries. This review provides an inclusive insight into the world of microbial exopolysaccharides covering its major aspects, namely- its types, biosynthesis and the factors that influence its production along with various techniques used for its recovery and further characterization. Special emphasis is placed on the applications of EPS in various large-scale commercial and industrial sectors.

Microbial exopolysaccharides (EPS) are an abundant and important group of compounds that can be secreted by bacteria, fungi and algae. The biotechnological production of these substances represents a faster alternative when compared to chemical and plant-derived production with the possibility of using industrial wastes as substrates, a feasible strategy after a comprehensive study of factors that may affect the synthesis by the chosen microorganism and desirable final product. Another possible difficulty could be the extraction and purification methods, a crucial part of the production of microbial polysaccharides, since different methods should be adopted. In this sense, this review aims to present the biotechnological production of microbial exopolysaccharides, exploring the production steps, optimization processes and current applications of these relevant bioproducts.

Diverse structural, functional and valuable polysaccharides are synthesized by bacteria of all taxa and secreted into the external environment. These polysaccharides are referred to as exopolysaccharides and they may either be homopolymeric or heteropolymeric in composition and of diverse high molecular weights (10 to 1000 kDa). The material properties of exopolysaccharides have revolutionized the industrial and medical sectors due to their retinue of functional applications and prospects. These applications have been extensive in areas such as pharmacological, nutraceutical, functional food, cosmeceutical, herbicides and insecticides among others, while prospects includes uses as anticoagulant, antithrombotic, immunomodulation, anticancer and as bioflocculants. Due to the extensive applications of bacterial exopolysaccharides, this overview provides basic information on their physiologic and morphologic functions as well as their applications and prospects in the medical and industrial sectors.

Microbial exopolysaccharides such as xanthan and dextran have been commercial products for many years; the search for new gelling agents has yielded gellan. Exopolysaccharides have many other novel properties to offer, and the discovery of immune modulation and tumouristasis by beta-D-glucans, and the use of bacterial cellulose in audio membranes and of hyaluronic acid in cosmetics provide some novel applications. Semisynthetic polymers and polysaccharides as sources of oligosaccharides and as enzyme substrates in the determination of enzyme specificity should further increase the interest in these macromolecules.

This study focuses on the optimisation of cheese whey formulated media for the production of hyaluronic acid (HA) by Streptococcus zooepidemicus. Culture media containing whey (W; 2.1g/L) or whey hydrolysate (WH; 2.4 g/L) gave the highest HA productions. Both W and WH produced high yields on protein consumed, suggesting cheese whey is a good nitrogen source for S. zooepidemicus production of HA. Polysaccharide concentrations of 4.0 g/L and 3.2g/L were produced in W and WH in a further scale-up to 5L bioreactors, confirming the suitability of the low-cost nitrogen source. Cheese whey culture media provided high molecular weight (>3000 kDa) HA products. This study revealed replacing the commercial peptone by the low-cost alternative could reduce HA production costs by up to a 70% compared to synthetic media.Copyright © 2015 Elsevier Ltd. All rights reserved.

Colanic acid (CA) is an extracellular polysaccharide produced by most Escherichia coli strains as well as by other species of the family Enterobacteriaceae. We have determined the sequence of a 23-kb segment of the E. coli K-12 chromosome which includes the cluster of genes necessary for production of CA. The CA cluster comprises 19 genes. Two other sequenced genes (orf1.3 and galF), which are situated between the CA cluster and the O-antigen cluster, were shown to be unnecessary for CA production. The CA cluster includes genes for synthesis of GDP-L-fucose, one of the precursors of CA, and the gene for one of the enzymes in this pathway (GDP-D-mannose 4,6-dehydratase) was identified by biochemical assay. Six of the inferred proteins show sequence similarity to glycosyl transferases, and two others have sequence similarity to acetyl transferases. Another gene (wzx) is predicted to encode a protein with multiple transmembrane segments and may function in export of the CA repeat unit from the cytoplasm into the periplasm in a process analogous to O-unit export. The first three genes of the cluster are predicted to encode an outer membrane lipoprotein, a phosphatase, and an inner membrane protein with an ATP-binding domain. Since homologs of these genes are found in other extracellular polysaccharide gene clusters, they may have a common function, such as export of polysaccharide from the cell.

Biofilms are assemblages of single or multiple populations that are attached to abiotic or biotic surfaces through extracellular polymeric substances. Gene expression in biofilm cells differs from planktonic stage expression and these differentially expressed genes regulate biofilm formation and development. Biofilm systems are especially suitable for the treatment of recalcitrant compounds because of their high microbial biomass and ability to immobilize compounds. Bioremediation is also facilitated by enhanced gene transfer among biofilm organisms and by the increased bioavailability of pollutants for degradation as a result of bacterial chemotaxis. Strategies for improving bioremediation efficiency include genetic engineering to improve strains and chemotactic ability, the use of mixed population biofilms and optimization of physico-chemical conditions. Here, we review the formation and regulation of biofilms, the importance of gene transfer and discuss applications of biofilm-mediated bioremediation processes.

Since its first description in the early 1960s, scleroglucan attracted much attention from both academia and industry. Scleroglucan is an exopolysaccharide secreted by the basidiomycete Sclerotium rolfsii and appreciated as a multipurpose compound applicable in many industrial fields, including oil industry, food industry and pharmacy. In this review, the current knowledge on scleroglucan chemistry, genetics, biosynthesis and production will be summarized and different application possibilities will be discussed. The biosynthesis of scleroglucan in S. rolfsii will be highlighted by recent transcriptomic data and linked to physiological data to better understand the biogenesis of scleroglucan and its link to the phytopathologic lifestyle of S. rolfsii.

The objective of this investigation was to evaluate the chitosans produced by several species of fungi.Representatives of four species of filamentous fungi, Aspergillus niger, Rhizopus oryzae, Lentinus edodes and Pleurotus sajo-caju, and two yeast strains, Zygosaccharomyces rouxii TISTR5058 and Candida albicans TISTR5239, were investigated for their ability to produce chitosan in complex media. Fungal chitosan was produced at 10-140 mg g-1 cell dry weight, had a degree of deacetylation of 84-90% and a molecular weight of 2.7 x 104-1.9 x 105 Da with a viscosity of 3.1-6.2 centipoises (cP).Rhizopus oryzae TISTR3189 was found to be the producer of the highest amounts of chitosan.Commercial chitosan could be obtained from Rhizopus mycelia and would have potential applications for medical and agricultural uses.

Biopolymers are considered a potential alternative to conventional chemical polymers because of their ease of biodegradability, high efficiency, non-toxicity and non-secondary pollution. Recently, extracellular polymeric substances (EPS, biopolymers produced by the microorganisms) have been recognised by many researchers as a potential flocculent for their applications in various water, wastewater and sludge treatment processes. In this context, literature information on EPS is widely dispersed and is very scarce. Thus, this review marginalizes various studies conducted so far about EPS nature-production-recovery, properties, environmental applications and moreover, critically examines future research needs and advanced application prospective of the EPS. One of the most important aspect of chemical composition and structural details of different moieties of EPS in terms of carbohydrates, proteins, extracellular DNA, lipid and surfactants and humic substances are described. These chemical characteristics of EPS in relation to formation and properties of microbial aggregates as well as degradation of EPS in the matrix (biomass, flocs etc) are analyzed. The important engineering properties (based on structural characteristics) such as adsorption, biodegradability, hydrophilicity/hydrophobicity of EPS matrix are also discussed in details. Different aspects of EPS production process such as bacterial strain maintenance; inoculum and factors affecting EPS production were presented. The important factors affecting EPS production include growth phase, carbon and nitrogen sources and their ratio, role of other nutrients (phosphorus, micronutrients/trace elements, and vitamins), impact of pH, temperature, metals, aerobic versus anaerobic conditions and pure and mixed culture. The production of EPS in high concentration with high productivity is essential due to economic reasons. Therefore, the knowledge about all the aspects of EPS production (listed above) is highly essential to formulate a logical and scientific basis for the research and industrial activities. One of the very important issues in the production/application/biodegradation of EPS is how the EPS is extracted from the matrix or a culture broth. Moreover, EPS matrix available in different forms (crude, loosely bound, tightly bound, slime, capsular and purified) can be used as a bioflocculant material. Several chemical and physical methods for the extraction of EPS (crude form or purified form) from different sources have been analyzed and reported. There is ample information available in the literature about various EPS extraction methods. Flocculability, dewaterability and biosorption ability are the very attractive engineering properties of the EPS matrix. Recent information on important aspects of these properties qualitatively as well as quantitatively has been described. Recent information on the mechanism of flocculation mediated by EPS is presented. Potential role of EPS in sludge dewatering and biosorption phenomenon has been discussed in details. Different factors influencing the EPS ability to flocculate and dewaterability of different suspensions have been included. The factors considered for the discussion are cations, different forms of EPS, concentration of EPS, protein and carbohydrate content of EPS, molecular weight of EPS, pH of the suspension, temperature etc. These factors were selected for the study based upon their role in the flocculation and dewatering mechanism as well the most recent available literature findings on these factors. For example, only recently it has been demonstrated that there is an optimum EPS concentration for sludge flocculation/dewatering. High or low concentration of EPS can lead to destabilization of flocs. Role of EPS in environmental applications such as water treatment, wastewater flocculation and settling, colour removal from wastewater, sludge dewatering, metal removal and recovery, removal of toxic organic compounds, landfill leachate treatment, soil remediation and reclamation has been presented based on the most recent available information. However, data available on environmental application of EPS are very limited. Investigations are required for exploring the potential of field applications of EPS. Finally, the limitations in the knowledge gap are outlined and the research needs as well as future perspectives are highlighted. Copyright © 2014 Elsevier Ltd. All rights reserved.

This paper reviews the formation, structure, and stability of bioaggregates with an emphasis on the composition and distribution of extracellular polymeric substances (EPS) and their role in bioaggregation. Bioaggregation is ubiquitous in natural environment and is of great importance in biological wastewater treatment processes. It greatly influences the flocculability, settleability, and dewaterability for flocs and sludge retention and shear resistance for biofilms. The physico-chemical and microbial structures of bioaggregates are dependent on operational conditions as well as microbial diversity and spatial distribution. The formation of bioaggregates is mediated by the physico-chemical interactions as well as the microbial interactions such as EPS production and quorum sensing. EPS are composed of a mixture of macromolecules including proteins, polysaccharides, humic-like substances, and nucleic acids, which entrap the microbial cells in a three-dimensional matrix. The composition and physico-chemical characteristics of EPS have significant influence on the maintenance of the bioaggregate structure and the process performance of the wastewater treatment. However, the mechanisms of bioaggregation are still unclear and the conclusions on the role of EPS were mostly drawn from the established correlations and hypotheses. This paper expects to provide up-to-date knowledge on bioaggregation and insights for further studies and applications.

The production of polyhydroxybutyrate (PHB) and extracellular polymeric substances (EPS) by Ralstonia eutropha ATCC 17699 at various glucose and (NH4)2SO4 concentrations in batch cultures were investigated. The biosynthesis of EPS by R. eutropha closely coupled with cell growth, while PHB was synthesized only under nitrogen-deficient and cell-growth-limited conditions. Experimental results show that the specific PHB production rate had an exponential correlation with both specific cell growth rate and EPS production rate. Furthermore, PHB was observed as the main storage of carbon and energy source by R. eutropha under nitrogen-limited conditions. In addition, experiments were conducted based on central composite design to optimize the batch culture for a high PHB yield. The PHB yield on glucose reached a maximum value of 0.34 g/g at glucose concentrations of 38.2 g/l and (NH4)2SO4 of 3.2 g/l.

Bacteria generate and attach countless glycan structures to diverse macromolecules. Despite this diversity, the mechanisms of glycoconjugate biosynthesis are often surprisingly similar. The focus of this review is on the commonalities between lipopolysaccharide (LPS) and glycoprotein assembly pathways and their evolutionary relationship. Three steps that are essential for both pathways are completed by membrane proteins. These include the initiation of glycan assembly through the attachment of a first sugar residue onto the lipid carrier undecaprenyl pyrophosphate, the translocation across the plasma membrane and the final transfer onto proteins or lipid A-core. Two families of initiating enzymes have been described: the polyprenyl-P N-acetylhexosamine-1-P transferases and the polyprenyl-P hexosamine-1-P transferases, represented by Escherichia coli WecA and Salmonella enterica WbaP, respectively. Translocases are either Wzx-like flippases or adenosine triphosphate (ATP)-binding cassette transporters (ABC transporters). The latter can consist either of two polypeptides, Wzt and Wzm, or of a single polypeptide homolog to the Campylobacter jejuni PglK. Finally, there are two families of conjugating enzymes, the N-oligosaccharyltransferases (N-OTase), best represented by C. jejuni PglB, and the O-OTases, including Neisseria meningitidis PglL and the O antigen ligases involved in LPS biosynthesis. With the exception of the N-OTases, probably restricted to glycoprotein synthesis, members of all these transmembrane protein families can be involved in the synthesis of both glycoproteins and LPS. Because many translocation and conjugation enzymes display relaxed substrate specificity, these bacterial enzymes could be exploited in engineered living bacteria for customized glycoconjugate production, generating potential vaccines and therapeutics.

Microalgae are photosynthetic microorganisms presenting a diversity of biotechnological applications. However, microalgal cultivation systems are not energetically and economically feasible. Possible strategies that can be applied to improve the feasibility of microalgal production include biofouling control in photobioreactors, the use of attached growth systems and bioflocculation. These processes are ruled by surface physicochemical properties. Accordingly, the surface physicochemical properties of Chlorella vulgaris, Pseudokirchneriella subcapitata, Synechocystis salina and Microcystis aeruginosa were determined through contact angle and zeta potential measurements. Additionally, mixed cultures of the selected microorganisms were performed. Sedimentation kinetics of the studied cultures was also evaluated to understand how surface physicochemical properties influence microalgal recovery.

Extracellular nucleic acids are found in different biological fluids in the organism and in the environment: DNA is a ubiquitous component of the organic matter pool in the soil and in all marine and freshwater habitats. Data from recent studies strongly suggest that extracellular DNA and RNA play important biological roles in microbial communities and in higher organisms. DNA is an important component of bacterial biofilms and is involved in horizontal gene transfer. In recent years, the circulating extracellular nucleic acids were shown to be associated with some diseases. Attempts are being made to develop noninvasive methods of early tumor diagnostics based on analysis of circulating DNA and RNA. Recent observations demonstrated the possibility of nucleic acids exchange between eukaryotic cells and extracellular space suggesting their participation in so far unidentified biological processes.(c) 2007 Wiley Periodicals, Inc.

Pseudomonas aeruginosa produces glycolipidic surface-active molecules (rhamnolipids) which have potential biotechnological applications. Rhamnolipids are produced by P. aeruginosa in a concerted manner with different virulence-associated traits. Here, we review the rhamnolipids biosynthetic pathway, showing that it has metabolic links with numerous bacterial products such as alginate, lipopolysaccharide, polyhydroxyalkanoates, and 4-hydroxy-2-alkylquinolines (HAQs). We also discuss the factors controlling the production of rhamnolipids and the proposed roles this biosurfactant plays in P. aeruginosa lifestyle.

Many microorganisms secrete extracellular biopolymeric flocculants (EBFs) in the culture broth. This work reviews the development of EBF research and applications. Aspects discussed include a comparison of the chemical and biological flocculating agents, isolation of EBF-producing microorganisms, culture conditions, mechanisms of flocculation, the chemical structure of EBFs, and the role of physicochemical factors in the flocculating activity.

The extracellular polymeric substances (EPS) contained in activated sludge flocs resulting from two-sewage treatment plants were extracted according to eight methods referred to in the bibliography. Extracted EPS were characterized by their extraction yield, carbon concentration, their biochemical composition, their HPSEC chromatograms and, where possible, molecular weight (MW) distributions. With HPSEC chromatograms, the use of the mobile phase containing methanol allowed a hydrophobic mechanism for EPS, extracted partly by chemical methods, to be identified. An MW distribution (from 0.1 to 600kDa) was established for EPS extracted by control and physical methods only, from calibration. Except for the resin and heating extraction methods, the EPS extracted from the two sludges displayed the same trend in their HPSEC fingerprints but not in their MW distribution. Results show that the extraction methods using chemical reagents strongly affected the HPSEC fingerprints of EPS, whereas, the physical methods influenced only MW distribution but not HPSEC fingerprints. The use of heat to extract EPS seems to induce hydrolysis of a part of EPS. The HPSEC fingerprint is a good indicator for the appreciation of the consequences of EPS extraction methods on the EPS extracted and the distribution of EPS with low MW in particular.

Extracellular polymeric substance (EPS)-mineral associations occur naturally in soil and sediments, and they might play crucial roles in heavy metals immobilization. In this study, EPS-montmorillonite composites with different weight ratios were characterized and investigated for their Cd(II) sorption behavior. The results showed that the EPS chains can intercalate into montmorillonite layers by hydrogen bonding connection and chemical reaction between CO, C-N and COO groups with interlayer cations of montmorillonite, therefore promoting delamination of montmorillonite, especially under a lower weight ratio. An enhancement adsorption of heavy metals was obtained with the composites at lower weight ratios of 1:50 and 0.5:50, whereas composites with higher weight ratio of 5:50 presented a reduced adsorption ability, demonstrating that adsorption of Cd(II) onto the EPS-montmorillonite composites was weight ratio dependent. AFM, CLSM, FT-IR and XPS analysis illustrated that the enhancement of sorption under low weight ratio can be attributed to the release of surface active sites of EPS because of reduced aggregation, the increase of negative surface charges when EPS and montmorillonite were interacted and additional bridging of cadmium ions between EPS and montmorillonite. These findings extend the knowledge into the mobility and fate of Cd(II) in organic matter rich soils and sediments.Copyright © 2019 Elsevier Ltd. All rights reserved.

The management of wastewater sludge, now often referred to as biosolids, accounts for a major portion of the cost of the wastewater treatment process and represents significant technical challenges. In many wastewater treatment facilities, the bottleneck of the sludge handling system is the dewatering operation. Advanced sludge treatment (AST) processes have been developed in order to improve sludge dewatering and to facilitate handling and ultimate disposal. The authors have extensively reported lab-scale, semi-pilot and pilot investigations on either thermal and thermochemical processes, or chemical oxidation using hydrogen peroxide. To understand the action of these advanced sludge technologies, the essential role played by extracellular polymeric substances (EPS) needs to be understood. EPS form a highly hydrated biofilm matrix, in which the micro-organisms are embedded. Hence they are of considerable importance in the removal of pollutants from wastewater, in bioflocculation, in settling and in dewatering of activated sludge. The present paper reviews the characteristics of EPS and the influence of thermochemical and oxidation mechanisms on degradation and flocculation of EPS. Experimental investigations on waste activated sludge are conducted by the authors to evaluate the various literature findings. From the experiments, it is concluded that AST methods enhance cake dewaterability in two ways: (i) they degrade EPS proteins and polysaccharides reducing the EPS water retention properties; and (ii) they promote flocculation which reduces the amount of fine flocs.Copyright 2003 Elsevier B.V.

Redox cycling of extracellular electron shuttles can enable the metabolic activity of subpopulations within multicellular bacterial biofilms that lack direct access to electron acceptors or donors. How these shuttles catalyze extracellular electron transfer (EET) within biofilms without being lost to the environment has been a long-standing question. Here, we show that phenazines mediate efficient EET through interactions with extracellular DNA (eDNA) in Pseudomonas aeruginosa biofilms. Retention of pyocyanin (PYO) and phenazine carboxamide in the biofilm matrix is facilitated by eDNA binding. In vitro, different phenazines can exchange electrons in the presence or absence of DNA and can participate directly in redox reactions through DNA. In vivo, biofilm eDNA can also support rapid electron transfer between redox active intercalators. Together, these results establish that PYO:eDNA interactions support an efficient redox cycle with rapid EET that is faster than the rate of PYO loss from the biofilm.Copyright © 2020 Elsevier Inc. All rights reserved.

In microbiologically influenced corrosion (MIC) caused by sulfate-reducing bacteria (SRB), extracellular electron transfer (EET) between metals and microorganisms affects the metal corrosion process. In this work, the effect of the electron mediator riboflavin on the EET-MIC behavior of 2024 aluminum alloy (AA2024) was investigated by electrochemical methods, surface analysis techniques, focused ion beam, scanning electron microscopy, and x-ray photoelectron spectroscopy techniques. The results showed that the electron mediator was significantly able to accelerate SRB attack against AA2024. SRB utilized to consume H+ to accelerate its own metabolism and promoted the corrosion of AA2024, resulting in the formation of corrosion product AlOOH and Al(OH)3. The addition of electron mediator riboflavin increased the electron transfer efficiency and affected the reaction rate constant to accelerate the corrosion rate of aluminum alloy. The addition of 10 ppm riboflavin led to denser corrosion product biofilms on the surface of the aluminum alloy, which accelerated the formation of NaAlO2. Cl− diffused into the film layer through the pores of the surface of the aluminum alloy and was adsorbed into the film layer to induce pitting corrosion on the surface of the aluminum alloy. A large amount of SRB was attached, which resulted in an increasing pit depth on the surface of the aluminum alloy. Riboflavin accelerated the electron transfer process from the surface of the aluminum alloy across the cell wall to the cytoplasm, which led to serious corrosion of the aluminum alloy. The distribution of SRB in biofilm and the longitudinal distribution of bacteria in the process of pitting corrosion showed that the addition of electron mediators increased the depth of pits in aluminum alloys. Bacteria in the pitting area gathered at the bottom of the biofilm, and the pits were rich in Ca, P, and other elements.

Corrosion of metals is a serious and challenging problem faced worldwide by industry. Purified Leuconostoc mesenteroides exopolysaccharide (EPS) coatings, cast from aqueous solution, inhibited the corrosion of low-carbon steel as determined by electrochemical impedance spectroscopy (EIS). There were two different corrosion behaviors exhibited when EPS films from different strains were cast onto the steel. One EPS coating reacted immediately with the steel substrate to form an iron (III) oxide layer ("rust") during the drying process while another did not. The samples that did not flash corrode had higher corrosion inhibition and formed an iron (II) passivation layer during EIS testing that persisted after the cells were disassembled. Corrosion inhibition was strain-specific as polysaccharides with similar structure did not have the same corrosion potential.

\n Microbiologically influenced corrosion (MC) of steel has been attributed to the activity of biofilms that include anaerobic microorganisms such as iron-respiring bacteria, yet the mechanisms by which these organisms influence corrosion have been unclear. To study this process, we generated mutants of the iron-respiring bacterium\n Shewanella oneidensis\n strain MR-1 that were defective in biofilm formation and/or iron reduction. Electrochemical impedance spectroscopy was used to determine changes in the corrosion rate and corrosion potential as a function of time for these mutants in comparison to the wild type. Counter to prevailing theories of MC, our results indicate that biofilms comprising iron-respiring bacteria may reduce rather than accelerate the corrosion rate of steel. Corrosion inhibition appears to be due to reduction of ferric ions to ferrous ions and increased consumption of oxygen, both of which are direct consequences of microbial respiration.\n

Here, we measured the concentrations of several ions in cultivated Gram-negative and Gram-positive bacteria, and analyzed their effects on polymer formation by the actin homologue MreB. We measured potassium, sodium, chloride, calcium and magnesium ion concentrations in Leptospira interrogans, Bacillus subtilis and Escherichia coli. Intracellular ionic strength contributed from these ions varied within the 130-273 mM range. The intracellular sodium ion concentration range was between 122 and 296 mM and the potassium ion concentration range was 5 and 38 mM. However, the levels were significantly influenced by extracellular ion levels. L. interrogans, Rickettsia rickettsii and E. coli MreBs were heterologously expressed and purified from E. coli using a novel filtration method to prepare MreB polymers. The structures and stability of Alexa-488 labeled MreB polymers, under varying ionic strength conditions, were investigated by confocal microscopy and MreB polymerization rates were assessed by measuring light scattering. MreB polymerization was fastest in the presence of monovalent cations in the 200-300 mM range. MreB filaments showed high stability in this concentration range and formed large assemblies of tape-like bundles that transformed to extensive sheets at higher ionic strengths. Changing the calcium concentration from 0.2 to 0 mM and then to 2 mM initialized rapid remodelling of MreB polymers.

Biosorption of Cr(VI) using native strains of cyanobacteria from metal contaminated soil in the premises of textile mill has been reported in this paper. Biosorption was studied as a function of pH (1-5), contact time (5-180 min) and initial chromium ion concentration (5-20mg/l) to find out the maximum biosorption capacity of alginate immobilized Nostoc calcicola HH-12 and Chroococcus sp. HH-11. The optimum conditions for Cr(VI) biosorption are almost same for the two strains (pH 3-4, contact time 30 min and initial chromium concentration of 20mg/l) however, the biomass of Chroococcus sp. HH-11 was found to be more suitable for the development of an efficient biosorbent for the removal of Cr(VI) from wastewater, as it showed higher values of q(m) and K(f), the Langmuir and Freundlich isotherm parameters. Both the isotherm models were suitable for describing the biosorption of Cr(VI) by the cyanobacterial biosorbents.

\n The bacterium\n Shewanella oneidensis\n is well known to use extracellular electron sinks, metal oxides and ions in nature or electrodes when cultured in a fuel cell, to power the catabolism of organic material. However, the power density of microbial fuel cells has been limited by various factors that are mostly related to connecting the microbes to the anode. Cao\n et al\n. found that a reduced graphene oxide–silver nanoparticle anode circumvents some of these issues, providing a substantial increase in current and power density (see the Perspective by Gaffney and Minteer). Electron microscopy revealed silver nanoparticles embedded or attached to the outer cell membrane, possibly facilitating electron transfer from internal electron carriers to the anode. —MAF\n

\n Safe and effective nuclear waste disposal, as well as accidental radionuclide releases, necessitates our understanding of the fate of radionuclides in the environment, including their interaction with microorganisms. We examined the sorption of Pu(IV) and Pu(V) to\n Pseudomonas\n sp. strain EPS-1W, an aerobic bacterium isolated from plutonium (Pu)-contaminated groundwater collected in the United States at the Nevada National Security Site (NNSS) in Nevada. We compared Pu sorption to cells with and without bound extracellular polymeric substances (EPS). Wild-type cells with intact EPS sorbed Pu(V) more effectively than cells with EPS removed. In contrast, cells with and without EPS showed the same sorption affinity for Pu(IV).\n In vitro\n experiments with extracted EPS revealed rapid reduction of Pu(V) to Pu(IV). Transmission electron microscopy indicated that 2- to 3-nm nanocrystalline Pu(IV)O\n 2\n formed on cells equilibrated with high concentrations of Pu(IV) but not Pu(V). Thus, EPS, while facilitating Pu(V) reduction, inhibit the formation of nanocrystalline Pu(IV) precipitates.\n