Bacterial Extracellular Polymeric Substances Research Articles

Protein profile of bacterial extracellular polymeric substance by Fourier transform infrared spectroscopy

Self-adherent bacterial communities are embedded into biofilms, these densely packed and distinctive microbial matrices are surrounded by extracellular polymeric substances (EPS). The growth surface of bacteria, environmental conditions and harvesting methods may alter the biochemical composition of secreted EPS and the selection of EPS isolation method has critical role on analysis. In the present study, EPS produced by various strains were extracted using two extraction methods including liquid (broth) or solid (agar) media. The biomolecular content of resulting extracts were investigated for comparative analysis of different EPS isolation methods. EPS composition of each strain was analyzed by Fourier transform infrared spectroscopy (FTIR), a non-common technique for foodborne pathogen researches. According to the FTIR analysis results of the samples extracted by liquid media technique, some additional peaks were observed at 1397 cm−1 and 1230 cm−1. These peaks cannot be observed for solid media samples, two of the molecular fingerprints were disappeared and the protein content have found decreased. Similar results obtained from conventional protein assay (Bradford), 8 out of 10 samples of liquid extraction method were also shown to be significantly higher in comparison solid extraction method (p < 0.05). These findings confirm the feasibility of FTIR for EPS researches and importance of method selection for the detection of biomolecular fingerprints.

Directing Effect of Bacterial Extracellular Polymeric Substances (EPS) on Calcite Organization and EPS–Carbonate Composite Aggregate Formation

Mineralized structures generated under biological control are hierarchical composites that consist of biopolymer matrices and minerals. The biopolymer matrix in biological material is developed as ...

Revealing soil‐borne hydrogel effects on soil hydraulic properties using a roughness‐triangular pore space model

AbstractUnderstanding the influence of soil‐borne hydrogels (e.g., bacterial extracellular polymeric substances [EPS] and biofilm or root‐derived mucilage) on soil hydraulic properties is crucial for accurate modeling of flow and transport in porous media. The underlying mechanisms of how hydrogels modify soil physical and hydraulic properties, however, remain unclear. In this study, we applied a roughness‐triangular pore space model (R‐TPSM) to simulate water retention curve and hydraulic conductivity of hydrogel‐affected soils. The model considers the effective soil pore size distribution and physicochemical properties (e.g., surface tension and surface roughness) of soil and soil solution. The modeling results are in good agreement with measured water retention curves and hydraulic conductivity for different textured soils. Comparison of the fitted model parameters between control and hydrogel‐treated soil samples indicates that hydrogels reduce surface tension and shift the effective pore size distribution to a narrower size range. Hydrogels generally increase water retention in the form of adsorptive films and reduce film flow under relatively dry conditions. This study highlights the importance of considering reduced surface tension and mean pore size by hydrogels in changing soil hydraulic properties, which has important implications for accurate modeling of water distribution and flow in the rhizosphere.

Application of bacterial extracellular polymeric substances for detoxification of heavy metals from contaminated environment: A mini-review

In recent years, advanced research progress has been widely developed in regard to bioremediation of heavy metal pollution by using bacteria. The biopolymer of bacteria i.e. the extra cellular polymeric substances displays noble physiological, Rheological and physico-chemical properties with special reference to the metal ion sequestration from polluted environment. This paper enlightens the role of exoploysachharide in biomineralization process and their effect on heavy metal sorption mechanism. Moreover, it also discusses heavy metal sorption abilities of EPS by elucidating the mechanism of action and remediation. Based on the review of literatures, further potential work is needed in this context to entangle the mechanistic role of EPS and also explore the cell surface morphology of bacteria for better sorption and exclusion of heavy metals.

Role of extracellular polymeric substance (EPS) in toxicity response of soil bacteria Bacillus sp. S3 to multiple heavy metals.

Heavy metal resistant bacteria are of great interest because of their potential use in bioremediation. Understanding the survival and adaptive strategies of these bacteria under heavy metal stress is important for better utilization of these bacteria in remediation. The objective of this study was to investigate the role of bacterial extracellular polymeric substance (EPS) in detoxifying against different heavy metals in Bacillus sp. S3, a new hyper antimony-oxidizing bacterium previously isolated from contaminated mine soils. The results showed that Bacillus sp. S3 is a multi-metal resistant bacterial strain, especially to Sb(III), Cu(II) and Cr(VI). Toxic Cd(II), Cr(VI) and Cu(II) could stimulate the secretion of EPS in Bacillus sp. S3, significantly enhancing the adsorption and detoxification capacity of heavy metals. Both Fourier transform infrared spectroscopy (FTIR) and three-dimensional excitation-emission matrix (3D-EEM) analysis further confirmed that proteins were the main compounds of EPS for metal binding. In contrast, the EPS production was not induced under Sb(III) stress. Furthermore, the TEM-EDX micrograph showed that Bacillus sp. S3 strain preferentially transported the Sb(III) to the inside of the cell rather than adsorbed it on the extracellular surface, indicating intracellular detoxification rather than extracellular EPS precipitation played an important role in microbial resistance towards Sb(III). Together, our study suggests that the toxicity response of EPS to heavy metals is associated with difference in EPS properties, metal types and corresponding environmental conditions, which is likely to contribute to microbial-mediated remediation.

The viscosity behaviors of bacterial suspensions or extracellular polymeric substances and their effects on aerobic granular sludge.

Although the viscosity behavior of bacteria and extracellular polymeric substances (EPS) in flocculent activated sludge (FAS) and aerobic granular sludge (AGS) has been investigated, no studies have explored the role of viscosity in microbial attachment in pure culture. This study investigated the viscosity behavior of bacteria and EPS. The results showed that bacteria and their EPS exhibited non-Newtonian fluid and shear-thinning behavior. The viscosity of bacteria and EPS was 1.55-3.80cP and 1.10-2.40cP, respectively, while the attachment of bacteria (optical density at 600nm) was 0.1426-3.1015. Bacteria with high attachment secreted EPS with a higher viscosity (2.40cP), whereas those with weak attachment expressed EPS with a lower viscosity (1.10cP). Viscosity and microbial attachment or extracellular polysaccharide (PS) content were significantly positively correlated. PS content was the source of bacterial viscosity, and β-polysaccharide played a more important role in viscosity and microbial attachment than α-polysaccharide. Thus, viscosity plays a critical role in microbial attachment, and high viscosity and PS content result in high microbial attachment, which is beneficial to the granulation process of AGS.

A dolomitization event at the oceanic chemocline during the Permian-Triassic transition: REPLY

The Permian-Triassic boundary (PTB) crisis caused major shortterm perturbations in ocean chemistry, as recorded by the precipitation of anachronistic carbonates. Here, we document for the first time a global dolomitization event during the Permian-Triassic transition based on Mg/(Mg + Ca) data from 22 sections with a global distribution representing shallow- to deep-marine environments. Ten of these sections show high Mg/(Mg + Ca) ratios bracketing the PTB, recording a short-term spike in dolomite formation. The dolomite consists mainly of micron-scale anhedral to subhedral crystals that are associated with abundant fossilized bacterial bodies and extracellular polymeric substances, suggesting that dolomite precipitation was induced by microbial metabolic activity. Sections showing a dolomite spike at the PTB are widely distributed geographically, but mostly encountered in mid-shelf to upper-slope settings. Because the dolomitization event coincided with a rapid expansion of oceanic anoxia and high rates of sulfate reduction, we hypothesize that it was triggered by enhanced microbial sulfate reduction within the oceanic chemocline.

Potential role of bacterial extracellular polymeric substances as biosorbent material for arsenic bioremediation

Carcinogenic effects of arsenic through consumption of contaminated water are an alarming threat and there is an emergent need to reduce extremely high levels of toxic arsenic from environment. Bacterial biofilms produce polyanionic extracellular polymeric substance (EPS) that is considered an excellent biosorbent material for the remediation of toxic metals and metalloids. This study was aimed to investigate the role of bacterial EPS in arsenic bioremediation. EPS was extracted from biofilm forming and arsenic reducer bacterial strains that were isolated from industrial waste water and characterized biochemically. Fourier transform infrared spectroscopy was also performed to study functional groups. Both Exiguobacterium profundum PT2 and Ochrobactrum ciceri SW1 exhibited enhanced EPS production in the presence of arsenic. Arsenic stress increased protein and carbohydrate contents in the EPS of both bacterial strains as indicated by the peaks of 1363 to 1613 and 1035 to 1218 cm−1 wavenumbers, respectively to cope with arsenic present in the surroundings. Shifting of peaks in As5+ treated samples from 1363 to 1379, 847 to 800 and 1211 to 1134 cm−1 demonstrated the involvement of proteins, carbohydrates and phosphates in the sequestration of arsenic. Scanning electron microscopic examination of EPS revealed structural alterations such as the presence of closely embedded large clumps with interstitial spaces between stacked layers of the EPS of E. profundum PT2 treated with As5+ displayed the enhanced polysaccharide content and arsenic sorption. Therefore, increased production of bacterial EPS with large number of polyanionic functional groups on its surface having tendency to sequester arsenic through electrostatic or covalent interactions presented EPS an excellent biosorbent material for arsenic bioremediation.

Microalgal–Bacterial Flocs and Extracellular Polymeric Substances: Two Essential and Valuable Products of Integrated Algal Pond Systems

The integrated algal pond system (IAPS) is a passive wastewater treatment technology that can be used to remediate liquid waste from domestic, industrial and agricultural sources. The system exploits the mutualistic interaction between microalgae and bacteria to generate water of a quality suitable for discharge and/or reuse. During the treatment process, biomass in the form of microalgal–bacterial flocs (MaB-flocs) is generated, and this can be harvested and beneficiated in downstream processing. Here, we review literature on MaB-floc and extracellular polymeric substance (EPS) formation and discuss how essential microalgal–bacterial mutualism is at effecting IAPS-based wastewater treatment. Aggregation of microalgae and bacteria into MaB-flocs is clearly an outcome of EPS production by these microorganisms and arises for purposes of chemical and developmental interaction, protection, communication, aggregation and adhesion. The polymeric compounds which form the scaffold of this extracellular matrix comprise polysaccharides, proteins, uronic acid and nucleic acid. Natural EPS can be used as bioflocculant in water purification and in the dewatering and settling of sludge and is therefore an ideal natural replacement for commercially available synthetic polymers. Additionally, EPS are considered high value and can be used in many commercial applications. Thus, and to ensure sustained MaB-floc production in IAPS-based wastewater treatment plants, it is important that correct levels of EPS are maintained to facilitate settling and biomass recovery. Furthermore, it is the associated environmental and operational conditions that most impact EPS production and in turn, MaB-floc formation, and quality of the final IAPS-treated water.

Role of bacterial extracellular polymeric substances (EPS) in uptake and accumulation of co-contaminants

Coexistence of many contaminants in effluents discharged from industries is a serious environmental concern, even though these contaminants can individually be transformed into less toxic forms, but very few studies have reported simultaneous treatment of such contaminants. Present work was aimed at investigating the capability of extracellular polymeric substances from Bacillus subtilis MB378 for simultaneous uptake and accumulation of malachite green dye and selected metals (Cr, Cu and Cd). EPS showed highest uptake of cadmium (95.31%) at a rate of 1.04 mg g−1 without any dye addition. Chromium removal efficiency of 91.12% combined with malachite green was observed with a unit adsorption rate of 0.54 mg g−1, while 90.98% of copper removal was recorded in the presence of malachite green dye with highest binding capacity of 1.84 mg g−1 compared to individual metal ions. However, a reduction in color removal efficiency was noticed for malachite green in combination with metals compared to dye molecules alone. Quantification of decolorization revealed 94.91% removal of dye molecules by bacterial cells with EPS following bacterial cells without EPS (87.02%) and EPS (82.34%). Highest dye binding affinities of 0.66 and 0.64 mg g−1 were observed on combining the dye with chromium and cadmium, respectively. The formation of new peaks, disappearance and shifting of exiting in the UV–Vis absorption and FTIR spectra suggested possible adsorption and accumulation of dye combined with metals onto the charged or ionizable functional groups present on EPS surface, indicating EPS from B. subtilis MB378 as promising adsorbent in terms of potential pollutant removal and remediation.

A Mechanistic Study of Au(III) Removal from Solution by Bacillus subtilis

Bacteria–Au interactions control the fate of Au in a variety of geologic systems. Although previous studies have determined that non-metabolizing Bacillus subtilis cells can remove Au(III) from solution via cell surface adsorption reactions, and that upon removal Au(III) is rapidly reduced to Au(I) and remains bound to the cell surface, the mechanism of Au(III) removal by B. subtilis is poorly understood. This study provides further constraints on the mechanisms responsible for Au(III) removal by B. subtilis by conducting batch Au(III) removal experiments as a function of pH and Au loading (Au:biomass ratio) using biomass with and without two different types of treatment: (1) a treatment to remove extracellular polymeric substances (EPS) from the biomass, and (2) a treatment to irreversibly block surface sulfhydryl sites from Au binding. The experimental results suggest that Au(III) removal can be attributed primarily to Au complexation with bacterial sulfhydryl sites, but that Au–amino binding is also important under some conditions. Our experiments also suggest that Au–sulfhydryl binding occurs predominantly on EPS molecules produced by B. subtilis, and that Au–amino binding is also important and is located within the bacterial cell envelope. These findings are the first to constrain the location of sulfhydryl-binding sites for B. subtilis biomass, and they are the first to demonstrate the important role played by bacterial EPS in the process of Au adsorption and reduction by bacteria.

Bacterial community enhances flocculation efficiency of Ettlia sp. by altering extracellular polymeric substances profile

This study examined the effects of a bacterial community and extracellular polymeric substances (EPS) on Ettlia sp. flocculation. The growth rate, flocculation efficiency (FE), bacterial community, and EPS profile of axenic and xenic Ettlia cultures were monitored during 46 days of cultivation. For the xenic culture, with a great abundance of growth-promoting and flocculation-inducing bacteria, the biomass density was 18.75% higher and its FE reached 100% in the mid-stationary phase. Moreover, microscopic observation and a quantitative analysis of the EPS revealed the exclusive presence of long filamentous EPS and more compact structure in the xenic Ettlia culture, possibly explaining its better FE. Notwithstanding, for the axenic culture, despite a lower biomass density and reduced abundance of EPS, its FE reached 92.54% in the mid-stationary phase. Thus, the role of the bacterial community was found to be supportive rather than vital for the high settleability of the self-flocculating Ettlia microalgal culture.

Microhydrological Niches in Soils: How Mucilage and EPS Alter the Biophysical Properties of the Rhizosphere and Other Biological Hotspots

Core Ideas Plant mucilage and bacterial extracellular polymeric substances (EPS) prevent the breakup of the soil liquid phase. Formation of continuous structures buffers soil hydraulic properties. The release of viscous polymeric substances represents a universal strategy. Plant roots and bacteria are capable of buffering erratic fluctuations of water content in their local soil environment by releasing a diverse, highly polymeric blend of substances (e.g. extracellular polymeric substances [EPS] and mucilage). Although this concept is well accepted, the physical mechanisms by which EPS and mucilage interact with the soil matrix and determine the soil water dynamics remain unclear. High‐resolution X‐ray computed tomography revealed that upon drying in porous media, mucilage (from maize [Zea mays L.] roots) and EPS (from intact biocrusts) form filaments and two‐dimensional interconnected structures spanning across multiple pores. Unlike water, these mucilage and EPS structures connecting soil particles did not break up upon drying, which is explained by the high viscosity and low surface tension of EPS and mucilage. Measurements of water retention and evaporation with soils mixed with seed mucilage show how these one‐ and two‐dimensional pore‐scale structures affect macroscopic hydraulic properties (i.e., they enhance water retention, preserve the continuity of the liquid phase in drying soils, and decrease vapor diffusivity and local drying rates). In conclusion, we propose that the release of viscous polymeric substances and the consequent creation of a network bridging the soil pore space represent a universal strategy of plants and bacteria to engineer their own soil microhydrological niches where stable conditions for life are preserved.

A dolomitization event at the oceanic chemocline during the Permian-Triassic transition

The Permian-Triassic boundary (PTB) crisis caused major shortterm perturbations in ocean chemistry, as recorded by the precipitation of anachronistic carbonates. Here, we document for the first time a global dolomitization event during the Permian-Triassic transition based on Mg/(Mg + Ca) data from 22 sections with a global distribution representing shallow- to deep-marine environments. Ten of these sections show high Mg/(Mg + Ca) ratios bracketing the PTB, recording a short-term spike in dolomite formation. The dolomite consists mainly of micron-scale anhedral to subhedral crystals that are associated with abundant fossilized bacterial bodies and extracellular polymeric substances, suggesting that dolomite precipitation was induced by microbial metabolic activity. Sections showing a dolomite spike at the PTB are widely distributed geographically, but mostly encountered in mid-shelf to upper-slope settings. Because the dolomitization event coincided with a rapid expansion of oceanic anoxia and high rates of sulfate reduction, we hypothesize that it was triggered by enhanced microbial sulfate reduction within the oceanic chemocline.

Marine Bacteria Provide Lasting Anticorrosion Activity for Steel via Biofilm-Induced Mineralization

Steel corrosion is a global problem in marine engineering. Numerous inhibitory treatments have been applied to mitigate the degradation of metallic materials; however, they typically have a high cost and are not environmental friendly. Here, we present a novel and "green" approach for the protection of steel by a marine bacterium Pseudoalteromonas lipolytica. This approach protects steel from corrosion in seawater via the formation of a biofilm followed by the formation of an organic-inorganic hybrid film. The hybrid film is composed of multiple layers of calcite and bacterial extracellular polymeric substances, exhibiting high and stable barrier protection efficiency and further providing an in situ self-healing activity. The process involving the key transition from biofilm to biomineralized film is essential for its lasting anticorrosion activity, which overcomes the instability of biofilm protection on corrosion. Therefore, this study introduces a new perspective and an option for anticorrosion control in marine environments.

Bacterial Extracellular Polymeric Substances Amplify Water Content Variability at the Pore Scale

The function of microbial communities in soil is inextricably linked with the complex physical, chemical and biological structure of the soil itself. Pore-scale water content controls the hydraulic connectivity of microbial communities and microbes’ access to aqueous and gaseous substrates. In turn, soil bacteria directly influence local moisture conditions through the secretion of extracellular polymeric substances (EPS). However, the effect of a soil’s physical geometry on EPS-mediated water retention is not well understood. In this study, we systematically measured the rate and extent of water evaporation from pore structures as a function of both EPS concentration and pore size. Three different chamber types were employed: (i) glass capillary tubes (1.2 mm pore diameter) to represent a uniform macropore geometry; (ii) emulated soil micromodels (pore widths ~ 10 µm to > 300 µm) to represent an aggregated sandy loam pore geometry; and (iii) microfluidic capillary arrays (uniform channels 20 µm wide) to represent a uniform micropore geometry. All chambers were initially saturated with dilute EPS solutions collected from stationary-phase Sinorhizobium meliloti cultures and then the infiltration of air was tracked over time. In the largest chambers, EPS concentration had no effect on the extent of evaporation or on the magnitude or variability of the evaporation rate. However, in the chambers with micropore-sized physical features, EPS concentration strongly influenced rate, extent, and variability of pore water evaporation. In micropores, higher EPS concentrations enhanced water retention and led to greater variability in pore-scale water distributions. In real soil, these phenomena could act together to promote the intermediate water contents associated with productive soil systems, and more variable pore-scale water distributions could increase microbial community diversity and the resiliency of soil systems.

Contact Behavior between Cells and Particles in Bioleaching of Precious Metals from Waste Printed Circuit Boards

Bioleaching of precious metals from waste printed circuit boards such as using cyanogenic cultures for extraction of gold and silver has gained considerable attention. It has the advantages of low cost and environmental friendliness. However, low efficiency hindered its industrialization. In this study, a novel strategy has been proposed to improve bioleaching efficiency. We applied optical microscopy to investigate the surface interactions between bacteria and silver particles in two-step bioleaching. Results showed that bacterial adsorption and extracellular polymeric substances (EPS) binding were the primary negative behavior that hindered the leaching reaction. Functional group analysis by Fourier-transform infrared spectroscopy indicated that carboxyl, hydroxyl, and amine groups were the main chemical structures responsible for the negative influences. Bacteria–metal interactions were reduced in the presence of polyvinylpyrrolidone (PVP), and the silver recovery increased 1.8 times. Imaging analysis ...

Mechanical interactions between bacteria and hydrogels

Mechanical interactions between bacterial cells and extracellular polymeric substance are essential in determining biofilm assembly and disassembly as well the mechanical characteristics of biofilms. However, the physics of these mechanical interactions in different cell culture conditions are poorly understood. We created typical artificial biofilm consisting of planktonic bacteria and hydrogel, in the absence of metabolic or regulatory effect. We have demonstrated that the cell culture medium can significantly affect the mechanical interactions between bacterial cells and hydrogels. The stiffness of the bacteria-hydrogel artificial biofilm cannot be simply attributed by the summation of the contribution from the bacteria and hydrogel based on the mathematical models and computational models. We have revealed that the tryptone component of Luria-Bertani broth medium plays an important role in stiffening effect of bacteria-hydrogel construct. Such significant stiffening effect can be explained by the following mechanism: the presence of tryptone in cell culture medium may enable the bacteria itself to crosslink the hydrogel polymer chains. Our findings have also demonstrated the synergy of modelling and innovative experiments which would potentially impact the biofilm control strategies.

Towards a better production of bacterial exopolysaccharides by controlling genetic as well as physico-chemical parameters.

Bacterial extracellular polymeric substances, which are basically bacterial metabolites, have currently become a subject of great concern of modern day microbiologists and biotechnologists. Among these metabolites, bacterial exopolysaccharides or EPS, in particular, have gained a significant importance. EPS are formed by the bacteria in their late exponential or stationary phase of growth under special situations for specific purposes. They take part in the formation of bacterial biofilms. There is a great diversity in the types of EPS. Strikingly enough, a same species of bacterium can produce different types of EPS under different situations. The importance of EPS is largely because of their different applications in various industries. Now that the bacterial EPS has got the potentiality to become an upcoming tool in various futuristic applications of human benefit, the focus currently develops towards how better they can be produced in the laboratory by promoting the favorable factors for their production. While studying with different EPS forming bacteria, both the intrinsic factors like genetic configuration of the bacteria and the extrinsic factors like culture conditions under the influence of different physico-chemical parameters in order to maximize the EPS production have been taken into consideration. Both the factors have proved their worth. Hence, towards a better outcome for EPS production, it is indicated that a genetic manipulation of the bacteria should be synchronized with a proper selection of its culture condition by controlling different physico-chemical parameters.

Applications of nisin for biofouling mitigation of reverse osmosis membranes

This study addresses the potential of application of nisin, a polycyclic antimicrobial peptide produced by Lactococcus lactis, as a novel biological agent for control/mitigation of biofilms formed by three different microorganisms: (i) Pseudomonas aeruginosa P60, (ii) Bacillus species, and (iii) a mixed culture of the two species. Nisin did not affect the growth rate of either strain, while the viability of Bacillus sp. was decreased, as compared to P. aeruginosa P60. Nisin was particularly effective for the dislodging of bacterial cells and extracellular polymeric substances (EPS) for P. aeruginosa P60. Water permeability of biofouled membranes was recovered by over 92% for all the bacterial strains investigated after nisin cleaning in a dead-end filtration system. Nisin has no detrimental effect on RO membrane and thus, has a potential as a biological agent for the mitigation of membrane biofouling.