High arsenic concentrations in groundwater are causing a humanitarian disaster in Southeast Asia. It is generally accepted that microbial activities play a critical role in the mobilization of arsenic from the sediments, with metal-reducing bacteria stimulated by organic carbon implicated. However, the detailed mechanisms underpinning these processes remain poorly understood. Of particular importance is the nature of the organic carbon driving the reduction of sorbed As(V) to the more mobile As(III), and the interplay between iron and sulphide minerals that can potentially immobilize both oxidation states of arsenic. Using a multidisciplinary approach, we identified the critical factors leading to arsenic release from West Bengal sediments. The results show that a cascade of redox processes was supported in the absence of high loadings of labile organic matter. Arsenic release was associated with As(V) and Fe(III) reduction, while the removal of arsenic was concomitant with sulphate reduction. The microbial populations potentially catalysing arsenic and sulphate reduction were identified by targeting the genes arrA and dsrB, and the total bacterial and archaeal communities by 16S rRNA gene analysis. Results suggest that very low concentrations of organic matter are able to support microbial arsenic mobilization via metal reduction, and subsequent arsenic mitigation through sulphate reduction. It may therefore be possible to enhance sulphate reduction through subtle manipulations to the carbon loading in such aquifers, to minimize the concentrations of arsenic in groundwaters.
A Gram-negative, arsenate-respiring and arsenite-oxidizing marine bacterium, NKSG1 T , was isolated from hydrothermal sediment at Santorini, Greece. Strain NKSG1 T was a facultatively anaerobic, motile, non-spore-forming, rod-shaped bacterium. Growth occurred optimally at 35-40 6C, between pH 5.5 and 9.0 and with 0.5-16 % NaCl. Energy was conserved by the aerobic oxidation of a range of complex substrates, carbohydrates and organic acids, or anaerobically by arsenate reduction, nitrate reduction coupled to the oxidation of organic carbon or lactate fermentation. Oxidation of arsenite and anaerobic nitrate-dependent oxidation of Fe(II) were facilitated by the presence of an organic carbon source. The DNA G+C content was 58.1 mol%. The major respiratory quinone was Q-9. The significant fatty acids were 16 : 1v9c, summed feature 3 (iso-15 : 0 2-OH/16 : 1v7c), 16 : 0 and 18 : 1v9c. Analysis of 16S rRNA gene sequences showed that strain NKSG1 T fits within the phylogenetic cluster of the genus Marinobacter and is most closely related to Marinobacter koreensis DD-M3 T (99.3 % similarity). The degree of relatedness with M. koreensis DSM 17924 T based on DNA-DNA hybridization was 56 %. The results of a polyphasic study indicated that strain NKSG1 T is a representative of a novel species within the genus Marinobacter, for which the name Marinobacter santoriniensis sp. nov. is proposed. The type strain is NKSG1 T (5DSM 21262 T 5NCIMB 14441 T 5ATCC BAA-1649 T ). The capacity for arsenic reduction or oxidation has not been demonstrated previously for this genus.The genus Marinobacter was designated by Gauthier et al. (1992) based on the type species Marinobacter hydrocarbonoclasticus. A further 19 species with validly published names have subsequently been included within the genus (Antunes et al., 2007; Gorshkova et al., 2003;Green et al., 2006;Gu et al., 2007;Guo et al., 2007; Kim et al., 2006;Liebgott et al., 2006;Martin et al., 2003; Romanenko et al., 2005;Shieh et al., 2003;Shivaji et al., 2005;Xu et al., 2008;Yoon et al., 2003Yoon et al., , 2004Yoon et al., , 2007; Marinobacter aquaeolei (Huu et al., 1999) has been proposed to be a synonym of Marinobacter hydrocarbonoclasticus (Marquez & Ventosa, 2005). These species are motile, halophilic, Gram-negative gammaproteobacteria isolated from saline terrestrial or, more typically, marine environments. Commonly, they are flagellate and rod-shaped, with ubiquinone-9 as the major respiratory quinone. In terms of metabolism, they are either facultatively anaerobic or strictly aerobic heterotrophs. Often, they are capable of dissimilatory nitrate reduction and, for some species, hydrocarbon degradation and/or fermentation have also been demonstrated. Strain NKSG1 T was isolated from the ninth subculture of an arsenate-reducing enrichment culture on Marinobacter medium (DSMZ medium 970) agar plates (at 25 u C). The enrichment culture inoculum (10 % v/v) comprised hydrothermal sediment from a shallow bay along the coast of Nea Kameni, situated within the flooded caldera of the G...
Deciphering the biotic and abiotic factors that control microbial community structure over time and along an environmental gradient is a pivotal question in microbial ecology. Carnoulès mine (France), which is characterized by acid waters and very high concentrations of arsenic, iron, and sulfate, provides an excellent opportunity to study these factors along the pollution gradient of Reigous Creek. To this end, biodiversity and spatiotemporal distribution of bacterial communities were characterized using T-RFLP fingerprinting and high-throughput sequencing. Patterns of spatial and temporal variations in bacterial community composition linked to changes in the physicochemical conditions suggested that species-sorting processes were at work in the acid mine drainage. Arsenic, temperature, and sulfate appeared to be the most important factors that drove the composition of bacterial communities along this continuum. Time series investigation along the pollution gradient also highlighted habitat specialization for some major members of the community (Acidithiobacillus and Thiomonas), dispersal for Acidithiobacillus, and evidence of extinction/re-thriving processes for Gallionella. Finally, pyrosequencing revealed a broader phylogenetic range of taxa than previous clone library-based diversity. Overall, our findings suggest that in addition to environmental filtering processes, additional forces (dispersal, birth/death events) could operate in AMD community.
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