Bioreduction performance of Cr(VI) by microbial extracellular polymeric substances (EPS) and the overlooked role of tryptophan

Light-induced reduction of silver ions to silver nanoparticles in aquatic environments by microbial extracellular polymeric substances (EPS)

Shear, in the form of vigorous aeration, is used to control fouling in membrane bioreactor (MBR) systems. However, shear also influences the physicochemical and biological properties of MBR biomass. The current study examines the relationship between the aeration intensity and extracellular polymeric substance (EPS) production in MBRs. Two identical submerged MBRs were operated in parallel but the aeration rate was three times greater in one of the MBRs. The concentrations of floc-associated and soluble EPS were monitored for the duration of the experiment. Microscopic images and floc-size measurements were also collected regularly. The membrane fouling potential of the biomass was quantified using the flux-step method. Increased aeration did not have a direct effect on soluble or floc-associated EPS production in the microfiltration MBRs. However, aeration intensity had a significant effect on predatory organisms. Large aquatic earthworms, Aeolosoma hemprichi, proliferated under lower shear conditions but were never observed in the high shear reactor. Predation by A. hemprichi resulted in increased floc-associated and soluble EPS production. Thus, the mixing conditions in the low shear MBR indirectly resulted in increased soluble EPS concentrations and higher fouling potential. This research suggests that predation can have a significant impact on the production rates of floc-associated and soluble EPS – key parameters driving membrane fouling in MBRs.

Chapter 13 - Microbial extracellular polymeric substance and impacts on soil aggregation

Spectroscopic fingerprints profiling the polysaccharide/protein/humic architecture of stratified extracellular polymeric substances (EPS) in activated sludge

Extracellular polymeric substances dependence of surface interactions of Bacillus subtilis with Cd2+ and Pb2+: An investigation combined with surface plasmon resonance and infrared spectra

BACKGROUNDCr(VI) is being increasingly used in a variety of fields, including electroplating, metallurgy, pigment synthesis and leather tanning. The possible application of a microbial extracellular polymeric substance (EPS) from Klebsiella sp. J1 with abundant functional groups in remediating Cr(VI) pollution in water system was demonstrated.RESULTSThe maximum biosorption capacity of EPS for Cr(VI) was found to be 53.3 mg g−1 at an EPS dose of 1.5 g L−1, which was better than the majority of reported biosorbents. The adsorption of EPS for Cr(VI) was a spontaneous and endothermic process. The removal mechanism of Cr(VI) in aquatic environments was explored qualitatively and quantitatively by Zeta‐potential meter, X‐ray photoelectron spectrometer (XPS) as well as Fourier transform infrared spectrometer. The superior Cr(VI) removal performance was attributed mainly to Cr(VI) adsorption on EPS via chelation and ion‐exchange sorption, and the efficient reduction (82.3%) of Cr(VI) to Cr(III) by benzenoid amine (–NH–) on EPS, followed by generated Cr(III) immobilization on the surface of EPS via surface physical sorption and chelation, which might control the reaction rate of Cr(VI) removal process.CONCLUSIONThe removal of Cr(VI) by EPS from Klebsiella sp. J1 was attributed mainly to simultaneous sorption and reduction of Cr(VI) by EPS. The results demonstrated that EPS from Klebsiella sp. J1 has great potential in treating Cr(VI)‐contaminated water. © 2018 Society of Chemical Industry

In this study, six different treatments involving extracellular polymeric substances (EPS) from Enterobacter sp. FM-1 (FM-1) (no EPS (control), original bacterial cells (FM-1), FM-1 cells with EPS artificially removed (EPS-free cells, EPS-R), different forms of EPS (soluble EPS (S-EPS), loosely bound EPS (LB-EPS) and tightly bound EPS (TB-EPS)) obtained from FM-1) and three types of soils (non-contaminated soil (NC soil), high-contamination soil (HC soil) and low-contamination soil (LC soil)) were used to investigate the impact of different EPS treatments on soil microbial community composition and their potential role in the remediation of heavy metal (HM)-contaminated soil. The results indicate that the EPS secreted by FM-1 played a vital role in changing soil pH and helped increase soil bio- HMs. In addition, EPS secretion by FM-1 helped increase the soil EPS-polysaccharide and EPS-nucleic acid contents; even in HC soil, where the HM content was relatively high, LB-EPS addition still increased the EPS-polysaccharide and EPS-nucleic acid contents in the soil by 1.18- and 15.54-fold, respectively. FM-1, LB-EPS and TB-EPS addition increased the soil invertase, urease and alkaline phosphatase activities and increased the soil organic matter (SOM), NH4+-N and available phosphorus (AP) contents, which helped regulate soil nutrient reserves. Moreover, the addition of different EPS fractions modified the soil microbial community composition to help microbes adapt to an HM-contaminated environment. In the HC and LC soils, where the HM content was relatively high, the soil bacteria were dominated by Protobacteria, while fungi in the soil were dominated by Ascomycota. Among the soil physicochemical properties, the soil SOM and NH4+-N contents and invertase activity significantly impacted the diversity and community composition of both bacteria and fungi in the soil.

Dynamics in the production of extracellular polymeric substances (EPS) were investigated for the benthic diatoms Cylindrotheca closterium (Ehrenberg) and Nitzschia sp. The effect of growth phase and light:dark conditions were examined using axenic cultures. Two EPS fractions were distinguished. Soluble EPS was recovered from the culture supernatant and represented polysaccharides that were only loosely associated with the cells. Bound EPS was extracted from the cells using warm (30° C) water and was more closely associated with the diatom aggregates. Concentrations of EPS exceeded internal concentrations of sugar throughout growth, indicating that EPS production is important in these organisms. Soluble and bound EPS revealed distinct differences in daily dynamics during the course of growth. Soluble EPS was produced continuously once cultures entered the stationary phase. During the stationary phase, chl a-normalized EPS production rates equaled 6.4 and 3.4 d−1 for C. closterium and Nitzschia sp., respectively. In contrast, production of bound EPS occurred only in the light and was highest during the exponential phase. Up to 90% of the attached EPS that was produced in the light was degraded during the subsequent dark period. The monosaccharide distribution of EPS was constant during the course of the experiment. The soluble EPS consisted of high amounts of galactose and glucuronic acid, relative to rhamnose, glucose, xylose/mannose, and galacturonic acid. In contrast, glucose was the dominant monosaccharide present in the bound EPS. These differences suggest that the production of the two distinct EPS fractions is under different metabolic controls and probably serves different cellular functions.

Dynamics in the production of extracellular polymeric substances (EPS) were investigated for the benthic diatoms Cylindrotheca closterium (Ehrenberg) and Nitzschia sp. The effect of growth phase and light:dark conditions were examined using axenic cultures. Two EPS fractions were distinguished. Soluble EPS was recovered from the culture supernatant and represented polysaccharides that were only loosely associated with the cells. Bound EPS was extracted from the cells using warm (30° C) water and was more closely associated with the diatom aggregates. Concentrations of EPS exceeded internal concentrations of sugar throughout growth, indicating that EPS production is important in these organisms. Soluble and bound EPS revealed distinct differences in daily dynamics during the course of growth. Soluble EPS was produced continuously once cultures entered the stationary phase. During the stationary phase, chl a‐normalized EPS production rates equaled 6.4 and 3.4 d−1 for C. closterium and Nitzschia sp., respectively. In contrast, production of bound EPS occurred only in the light and was highest during the exponential phase. Up to 90% of the attached EPS that was produced in the light was degraded during the subsequent dark period. The monosaccharide distribution of EPS was constant during the course of the experiment. The soluble EPS consisted of high amounts of galactose and glucuronic acid, relative to rhamnose, glucose, xylose/mannose, and galacturonic acid. In contrast, glucose was the dominant monosaccharide present in the bound EPS. These differences suggest that the production of the two distinct EPS fractions is under different metabolic controls and probably serves different cellular functions.

Application of dynamic membranes in anaerobic membranes in anaerobic membrane bioreactor systems

Cadmium is a major heavy metal found in polluted aquatic environments, mainly derived from industrial production processes. We evaluated the biosorption of solubilized Cd2+ using the extracellular polymeric substances (EPS) produced by Bacillus sp. MC3B-22 and Microbacterium sp. MC3B-10 (Microbactan); these bacteria were originally isolated from intertidal biofilms off the coast of Campeche, Mexico. EPS were incubated with different concentrations of cadmium in ultrapure water. Residual Cd2+ concentrations were determined by Inductive Coupled Plasma-Optic Emission Spectrometry and the maximum sorption capacity (Qmax) was calculated according to the Langmuir model. EPS were characterized by X-ray photoelectron spectroscopy (XPS) before and after sorption. The Qmax of Cd2+ was 97 mg g−1 for Microbactan and 141 mg g−1 for MC3B-22 EPS, these adsorption levels being significantly higher than previously reported for other microbial EPS. In addition, XPS analysis revealed changes in structure of EPS after biosorption and showed that amino functional groups contributed to the binding of Cd2+, unlike other studies that show the carbohydrate fraction is responsible for this activity. This work expands the current view of bacterial species capable of synthesizing EPS with biosorbent potential for cadmium and provides evidence that different chemical moieties, other than carbohydrates, participate in this process.

This review synthesizes the current understanding of the interactions between microorganisms, extracellular polymeric substances (EPS), and biochar and their collective application in environmental remediation. Microorganisms and their EPS play pivotal roles in biofilm formation, enhancing microbial resistance to environmental stress, and facilitating pollutant degradation. Biochar, derived from biomass pyrolysis, provides a porous structure that offers a habitat for microorganisms and is an efficient adsorbent for organic pollutants. The synergistic effects of microbial−EPS−biochar interactions improve pollutant removal capacity and soil fertility. The review highlights four fundamental mechanisms of these interactions: adhesion and interfacial processes, shelter and nutrient transfer, signaling, bioregulation, and microbial electron transfer with biochar. Integrating biochar with microbial systems has demonstrated potential in treating heavy metals (HM) and organic pollutants and enhancing soil properties. However, the review also identifies gaps in knowledge, and emphasizes the need for further research to elucidate the long-term effects of biochar on microbial communities and EPS and to optimize the application of these interactions for sustainable environmental management.Graphical

Bioremediation of heavy metals-contaminated sites by microbial extracellular polymeric substances – A critical view

Extracellular polymeric substances (EPS) are, along with microbial cells, the main components of the biological sludges used in wastewater treatment and natural biofilms. EPS play a major role in removing pollutants from water by means of sorption. The ability of soluble EPS (S-EPS) and bound EPS (B-EPS) derived from various bacterial aggregates (flocs, granules, biofilms) to bind at pH 7.0 ± 0.1 to two pharmaceutical substances, acetaminophen (ACE) and erythromycin ethylsuccinate (ERY), has been investigated using the fluorescence quenching method. Two intense fluorescence peaks, A (Ex/Em range, 200-250/275-380 nm) and B (Ex/Em range, 260-320/275-360 nm), corresponding respectively to the aromatic protein region and soluble microbial by-product-like region, were identified in a three-dimensional excitation-emission matrix of EPS samples. The fluorescence peak, which corresponds to humic-like substances, was also identified though at low intensity. The ability of EPS to bind ACE was found to exceed that for ERY. The aromatic protein fraction of EPS displays a slightly higher affinity for drugs than that shown by the soluble microbial by-product-like fraction. The S-EPS and B-EPS present the same affinity for ACE and ERY. The effective quenching constants (log K) derived from the Stern-Volmer Equation equaled at peak A (with S-EPS): 3.7 ± 0.2 to 4.0 ± 0.1 for ACE and 2.1 ± 0.3 to 2.7 ± 0.1 for ERY. With B-EPS, these values were 3.9 ± 0.1 to 4.0 ± 0.1 for ACE and 2.0 ± 0.2 to 2.6 ± 0.1 for ERY. Our results suggest that the weaker EPS affinity for ERY than for ACE serves to partially explain why only about 50-80 % of ERY is removed from wastewater at the treatment plant. Moreover, this work demonstrates that EPS from natural river biofilms are able to bind drugs, which in turn may limit the mobility of drugs in natural waters.

Mechanisms of conjugative transfer of antibiotic resistance genes induced by extracellular polymeric substances: Insights into molecular diversities and electron transfer properties