Isolation and Identification of Iron-reducing Bacteria Enterobacter sp. B4 and Its Reduction Mechanism of Cr(Ⅵ)

Contribution of pristine and reduced microbial extracellular polymeric substances of different sources to Cu(II) reduction

Decision letter: Listeria monocytogenes requires cellular respiration for NAD+ regeneration and pathogenesis

The role of extracellular polymeric substances (EPS) in the reduction of Cr(VI) by Pannonibacter phragmitetus BB

Promoting vivianite recovery: Crucial role of tightly-bound extracellular polymeric substances

Insights into the Cr(III) biosorption mechanism from tannery effluent using exopolysaccharides produced by the isolated Lysinibacillus capsici PB300 (T).

Hexavalent chromium reduction through redox electrolytic cell with urea and cow urine as anolyte

BACKGROUNDMicrobial reduction of Cr(VI) to the much less toxic Cr(III), although practiced for the treatment of liquid wastes has not been implemented for the treatment of groundwater due to the absence of electron donors (organic substrates) and the lack of data on inhibition of biological Cr(VI) removal. The objective of this work is to evaluate biological groundwater treatment systems that will achieve high Cr(VI) removal with addition of a low dose of organic substrate and to estimate inhibition of microbial Cr(VI) reduction under anaerobic and anoxic conditions.RESULTSBiomass acclimatized to Cr(VI) under anaerobic conditions exhibited a higher sensitivity to Cr(VI) compared with biomass acclimatized to Cr(VI) under anoxic conditions. No significant inhibition of microbial growth was observed under anaerobic conditions for initial groundwater Cr(VI) concentrations up to 2000 µg L−1, whereas no significant inhibition was obtained under anoxic conditions at Cr(VI) concentrations as high as 10 000 µg L−1.CONCLUSIONThis study demonstrates that anoxic biological systems treating groundwater can provide complete hexavalent chromium removal at initial hexavalent chromium concentrations as high as 10 000 µg L−1. In addition anaerobic conditions can support complete hexavalent chromium removal at initial hexavalent chromium concentrations as high as 2000 µg L−1. © 2016 Society of Chemical Industry

Unlocking interfacial electron transfer in biophotoelectrochemical processes: Role of extracellular polymeric substances in aquatic environments.

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.

Cryptochromes are blue light-activated photoreceptors found in multiple organisms with significant similarity to photolyases, a class of light-dependent DNA repair enzymes. Unlike photolyases, cryptochromes do not repair DNA and instead mediate blue light-dependent developmental, growth, and/or circadian responses by an as yet unknown mechanism of action. It has recently been shown that Arabidopsis cryptochrome-1 retains photolyase-like photoreduction of its flavin cofactor FAD by intraprotein electron transfer from tryptophan and tyrosine residues. Here we demonstrate that substitution of two conserved tryptophans that are constituents of the flavin-reducing electron transfer chain in Escherichia coli photolyase impairs light-induced electron transfer in the Arabidopsis cryptochrome-1 photoreceptor in vitro. Furthermore, we show that these substitutions result in marked reduction of light-activated autophosphorylation of cryptochrome-1 in vitro and of its photoreceptor function in vivo, consistent with biological relevance of the electron transfer reaction. These data support the possibility that light-induced flavin reduction via the tryptophan chain is the primary step in the signaling pathway of plant cryptochrome.

The reaction mechanisms Fe(II) abiotic oxidation produce ·OH by CaCO3-induced in acid mine drainage (AMD) are well-documented, but little is known about the influence of extracellular polymeric substances (EPS) secreted by microorganisms on Fe(II) oxidation in AMD. In this study, ·OH production was experimently measured from oxygenation of simulated AMD in the presence of EPS. The cumulative ·OH increased from 56.75 to 158.70 µM within 24h at pH 3 with the increase in EPS concentration from 0 to 12mg/L. An appropriate pH (about 6) and EPS (6mg/L) concentration were required for the moderate rate of Fe(II) oxidation. Besides, the yield of ·OH increased remarkably with the addition of Fe3+. In the presence of EPS, ·OH production is attributed mainly the complexation of Fe(II) with EPS, of which is rich of carboxyl and hydroxyl groups. The findings provide fundamental supplement of ·OH production from Fe(II) oxidation by microorganisms in natural AMD.

Effect of extracellular polymeric substances removal and re-addition on the denitrification performance of activated sludge: Carbon source metabolism, electron transfer and enzyme activity

Nowadays much effort has been devoted for the development of cost-effective and environmentally friendly processes to obtain extracellular polymeric substances (EPS) with high emulsifying and flocculation activities. The aim of this study was to evaluate the capacity of bacterial strains previously isolated from oil-contaminated areas to produce EPS with high emulsification and bioflocculant properties during cultivation in domestic and bilge wastewater and in industrial crude glycerol. A total of seven bacterial strains were screened for EPS production, from which two strains, Pseudomonas aeruginosa LVD-10 and Enterobacter sp. SW, were selected as potential EPS producers. EPS with high emulsifying capacity in olive oil (a maximum of 96.6 and 89.8% for strain SW and LVD-10, respectively) was produced using bilge wastewater as substrate. EPS with a slightly lower emulsifying capacity was obtained using crude glycerol. In addition, the flocculation activity of the EPS extracted from strains LVD-10 and SW grown on crude glycerol was considerably higher (81.6 and 73.3%, respectively) than that obtained with other substrates. This is the first study that points out that EPS with emulsifying and flocculation potential activity can be produced from bilge wastewater and crude glycerol. The production of biopolymers with broad biotechnological applications using low-cost substrates can be a means to valorise waste streams.

Extracellular polymeric substances mediate bioleaching/biocorrosion via interfacial processes involving iron(III) ions and acidophilic bacteria

The extraction of extracellular polymeric substances (EPS) from activated sludge and the absorption properties of chromium (VI) (Cr <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6+</sup> ) on EPS were examined in this experiment. The effects of adsorption time, pH, mass of EPS, and initial Cr <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6+</sup> concentration on Cr <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6+</sup> removal efficiency were investigated. The results indicated that high speed centrifugation was efficient in the extraction of EPS and caused less damage to cells, meanwhile EPS extracted by this method was efficient in the adsorption of Cr <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6+</sup> . The adsorption reached equilibrium when the adsorption time was 240 min. The adsorption rate and the unit adsorption capacity were 50.83% and 19.06 mg g <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> EPS respectively. The optimal pH and mass of EPS were 6 and 400 mg L <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> on the condition that the initial Cr <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6+</sup> concentration was 100 mg L <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> . The adsorption rate declined with the rising of initial Cr <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6+</sup> concentration, but the unit adsorption capacity increased. The results demonstrated that the EPS extracted from activated sludge would be applicable to removing Cr <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6+</sup> .