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Microbially mediated arsenate (As(V)) and Fe(III) reduction play important roles in arsenic (As) cycling in nature. Extracellular electron shuttles can impact microbial Fe(III) reduction, yet little is known about their effects on microbial As mobilization in soils. In this study, microcosm experiments consisting of an As-contaminated soil and microbial communities obtained from several pristine soils were conducted, and the effects of electron shuttles on As mobilization were determined. Anthraquinone-2,6-disulfonate (AQDS) and riboflavin (RF) were chosen as common exogenous and biogenic electron shuttles, respectively, and both compounds significantly enhanced reductive dissolution of As and Fe. Accumulation of Fe(II)-bearing minerals was also observed, which may lead to re-immobilization of As after prolonged incubation. Interestingly, Firmicutes-related bacteria became predominant in all microcosms, but their compositions at the lower taxonomic level were different in each microcosm. Putative respiratory As(V) reductase gene (arrA) analysis revealed that bacteria closely related to a Clostridia group, especially those including the genera Desulfitobacterium and Desulfosporosinus, might play significant roles in As mobilization. These results indicate that the natural soil microbial community can use electron shuttles for enhanced mobilization of As; the use of this type of system is potentially advantageous for bioremediation of As-contaminated soils., (Copyright © 2017 Elsevier B.V. All rights reserved.)

To investigate differences in culturable freshwater bacterioplankton between summer and winter, we examined specific bacterioplankton in the low temperature surface water of two shallow, hypereutrophic, temperate lakes in Japan over two winters, and compared our results with the previously published data. We used the size-exclusion assay method (SEAM), a cultivation-based approach that simply and effectively isolates typical freshwater bacterioplankton. The specific clusters detected in the winter samples were the Rhodoferax sp. BAL47 cluster (LimA and LimC), a predominant and ubiquitous freshwater lineage, and the LiUU-5-340 cluster. To confirm tolerance to low water temperature of winter-specific groups, we also compared growth rates at 5°C among several pure strains of typical freshwater bacterioplankton clusters belonging to the Rhodoferax sp. BAL47, Polynucleobacter necessarius, GKS98, LiUU-5-340, and IRD18C08 of the class Betaproteobacteria, and the Luna-1 and Luna-2 of the class Actinobacteria. Specific detectability of freshwater bacterioplankton clusters/subclusters by SEAM in the winter sample substantially correlated with the low temperature-specific growth characteristics of each isolate. Response to water temperature is a key control factor in freshwater bacterioplankton assemblage composition. These results provide important insights into the specific response to water temperature of several ubiquitous culturable freshwater bacterioplankton clusters inhabiting a temperate climate zone. [ABSTRACT FROM AUTHOR]

A novel dissimilatory antimonate [Sb(V)]-reducing bacterium, strain SVR, was isolated from soil of a former antimony (Sb) mine. Strain SVR coupled Sb(V) reduction to acetate oxidation with an apparent reduction rate of 2.4 mM d−1. The reduction of Sb(V) was followed by the precipitation and accumulation of white microcrystals in the liquid medium. The precipitates were initially small and amorphous, but they eventually developed to the crystal phase with a length > 50 µm. Strain SVR removed 96% of dissolved Sb as the precipitates. An X-ray diffraction analysis indicated that the microcrystals were the orthorhombic Sb trioxide (Sb 2 O 3), i.e. , valentinite. Phylogenetic and physiological analyses revealed that strain SVR is a member of the genus Geobacter. The cell suspension of strain SVR incubated with acetate and Sb(V) at pH 7.0 was able to form valentinite. Interestingly, at pH 8.0, the cell suspension formed another crystalline Sb 2 O 3 with a cubic structure, i.e. , senarmontite. Our findings provide direct evidence that Geobacter spp. are involved in Sb(V) reduction in nature. Considering its superior capacity for Sb removal, strain SVR could be used for the recovery of Sb and the individual productions of valentinite and senarmontite from Sb-contaminated wastewater. [Display omitted] • An anaerobic Sb(V)-reducing bacterium, Geobacter sp. SVR, was isolated. • Strain SVR reduced 5 mM Sb(V) completely within 2 d. • Following Sb(V) reduction, Sb was precipitated as Sb 2 O 3 microcrystals. • Orthorhombic or cubic Sb 2 O 3 microcrystals were formed depending on the pH. [ABSTRACT FROM AUTHOR]