As(III) oxidation and kinetic analysis by Herminiimonas arsenicoxydans-loaded electrospinning activated carbon fiber biofilms.

In this study, an integrated and assembled recyclable biofilm material was prepared by loading Herminiimonas arsenicoxydans (H. arsenicoxydans) onto electrospun biomass-activated carbon nanofibers (denoted as H. arsenicoxydans-BACFs films). The H. arsenicoxydans-BACFs biofilms showed an approximately 50% increase in As(III) removal rate for 50 mg/L during a 48-h incubation. Furthermore, the biofilms demonstrated satisfactory biocompatibility, ideal catalytic As(III) oxidation and excellent recyclability in cyclic reactions (at least 5 runs). The improved catalytic efficiency is mainly due to a large amount of biomass accumulation and biofilms formation on the surface of the BACF films. More important, the BACF films as an electron transport medium from an oxidized state to a reduced state promote the electron transfer of As(III) oxidation of H. arsenicoxydans. The dual factors can synergistically promote As(III) oxidation efficiency. The oxidation process of As(III) in the H. arsenicoxydans-BACFs composite biofilm reactor was more in line with the first-order kinetic equation, and the oxidation rate of As(III) by H. arsenicoxydans-BACF0.4 was the fastest. The H. arsenicoxydans-BACF films outperformed conventional catalytic materials and could represent biomaterials for the remediation of As(III)-contaminated wastewater.

Immobilization and redistribution process of As(V) during As(V)-bearing ferrihydrite reduction by Geobacter sulfurreducens under the influence of TiO2 nanoparticles.

The redistribution process of arsenate (As(V)) and the variation in As(V) content in different locations must be clarified to ensure low mobility of As(V) during microbial ferrihydrite reduction. In this study, we investigated As(V) immobilization and redistribution processes when ferrihydrite was incubated with Geobacter sulfurreducens in the presence of titanium dioxide (TiO2) nanoparticles. Our study results showed that, As(V) in the aqueous phase and ferrihydrite were redistributed on light minerals (goethite), heavy minerals (ferrihydrite and magnetite), and extracellular polymeric substances (EPS) induced by G. sulfurreducens during ferrihydrite reduction. Interestingly, we found that As(V) in the form of arsenate ion (AsO43-) was adsorbed by the functional groups of the EPS, while the formed FeII3(AsVO4)2 was wrapped in the network structure of EPS. Moreover, the addition of TiO2 nanoparticles did not promote but delayed the entire ferrihydrite reduction, As(V) immobilization and redistribution processes. Furthermore, changes in the aqueous arsenic and iron concentrations are closely related to the formation time of secondary minerals. Our study findings provide new insights into the As(V) immobilization process mediated by G. sulfurreducens under anaerobic conditions.

Quantifying the optimal strategy of population control of quorum sensing network in Escherichia coli.

Biological functions of bacteria can be regulated by monitoring their own population density induced by the quorum sensing system. However, quantitative insight into the system's dynamics and regulatory mechanism remain challenging. Here, we construct a comprehensive mathematical model of the synthetic quorum sensing circuit that controls population density in Escherichia coli. Simulations agree well with experimental results obtained under different ribosome-binding site (RBS) efficiencies. We present a quantitative description of the component dynamics and show how the components respond to isopropyl-ß-D-1-thiogalactopyranoside (IPTG) induction. The optimal IPTG-induction range for efficiently controlling population density is quantified. The controllable area of population density by acyl-homoserine lactone (AHL) permeability is quantified as well, indicating that high AHL permeability should be treated with a high dose of IPTG, while low AHL permeability should be induced with low dose for efficiently controlling. Unexpectedly, an oscillatory behavior of the growth curve is observed with proper RBS-binding strengths and the oscillation is greatly restricted by the bacterial death induced by toxic metabolic by-products. Moreover, we identify that the mechanism underlying the emergence of oscillation is determined by the negative feedback loop structure within the signaling. Bifurcation analysis and landscape theory are further employed to study the stochastic dynamic and global stability of the system, revealing two faces of toxic metabolic by-products in controlling oscillatory behavior. Overall, our study presents a quantitative basis for understanding and new insights into the control mechanism of quorum sensing system, providing possible clues to guide the development of more rational control strategy.

Mangrovibacterium lignilyticum sp. nov., a facultatively anaerobic lignin-degrading bacterium isolated from mangrove sediment.

An alkali lignin-degrading, Gram-stain-negative, rod-shaped, non-motile and facultatively anaerobic bacterium, designated BM_7T, was isolated from mangrove sediment of the supralittoral zone in the Jiulong river estuary, PR China. The cells of strain BM_7T were 0.4-0.6 µm wide and 1.0-8.5 µm long. Oxidase and catalase activities were positive. Strain BM_7T could grow at 10-37 °C (optimum, 25-28 °C), at pH 6.0-8.0 (optimum, pH 7.0) and in the presence of 0.5-6 % (w/v) NaCl (optimum, 2%). Phylogenetic analysis of 16S rRNA gene sequences indicated that strain BM_7T belonged to the genus Mangrovibacterium of the family Prolixibacteraceae. It showed the highest similarity to Mangrovibacterium diazotrophicum JCM 19152T (96.8 %), followed by Mangrovibacterium marinum KCTC 42253T (96.1%). The values of average nucleotide identity and DNA-DNA hybridization were calculated as 76.9, 24.3 and 76.1, 17.4 % between strain BM_7T with M. diazotrophicum JCM 19152T and M. marinum KCTC 42253T, respectively. The major respiratory quinone of strain BM_7T was MK-7. The polar lipids were detected as phosphatidylethanolamine, three unidentified phospholipids and four unidentified aminolipids. The dominant fatty acids consisted of iso-C15 : 0, anteiso-C15 : 0, C15 : 1 ω6c, iso-C17 : 0 3-OH, C17 : 1 ω6c, C17 : 0 3-OH and C17 : 0. The genome size of strain BM_7T is 5.6 Mb, with G+C content of 43.4 mol%. Based on the phylogenetic and phenotypic characteristics, strain BM_7T was considered to represent a novel species of the genus Mangrovibacterium, and the name Mangrovibacterium lignilyticum sp. nov. is proposed. The type strain is BM_7T (=MCCC 1A15882T=KCTC 72696T).

Artificially constructed quorum-sensing circuits are used for subtle control of bacterial population density.

Vibrio fischeri is a typical quorum-sensing bacterium for which lux box, luxR, and luxI have been identified as the key elements involved in quorum sensing. To decode the quorum-sensing mechanism, an artificially constructed cell-cell communication system has been built. In brief, the system expresses several programmed cell-death BioBricks and quorum-sensing genes driven by the promoters lux pR and PlacO-1 in Escherichia coli cells. Their transformation and expression was confirmed by gel electrophoresis and sequencing. To evaluate its performance, viable cell numbers at various time periods were investigated. Our results showed that bacteria expressing killer proteins corresponding to ribosome binding site efficiency of 0.07, 0.3, 0.6, or 1.0 successfully sensed each other in a population-dependent manner and communicated with each other to subtly control their population density. This was also validated using a proposed simple mathematical model.