Probing the biogeochemistry of arsenic: Response of two contrasting aquifer sediments from Cambodia to stimulation by arsenate and ferric iron

Abstract

Many millions of people worldwide are at risk of severe poisoning through exposure to groundwater contaminated with sediment-derived arsenic. An ever-increasing body of work is reinforcing the link between microbially-mediated redox cycling in aquifer sediments and the mobilisation of sorbed As(V) into groundwaters as the potentially more mobile and toxic As(III) anion. However, to date, few studies have examined the biogeochemical cycling of Fe and As species by microbes indigenous to Cambodian sediments. In this study two contrasting sediments, taken from a shallow As-rich reducing aquifer in the Kien Svay district of Cambodia, were used in a laboratory microcosm study. We present evidence to show that microbes present in these sediments are able to reduce Fe(III) and As(V) when provided with an electron donor, and that the two sediments respond differently to stimulation with Fe(III) and As(V). Shifts in the community composition of the two sediments after stimulation with As(V) suggest a potential role for members of the beta-Proteobacteria in As(V) reduction, a phylogenetic grouping known to contain microorganisms capable of As(III) oxidation, but not previously implicated in As(V) reduction. PCR-based analysis of the sediment microbial DNA using primers specific to the arrA gene, (a gene essential for microbial As(V) respiration), indicates the presence of microorganisms capable of dissimilatory As(V) reduction.

Arsenic(V) Reduction in Relation to Iron(III) Transformation and Molecular Characterization of the Structural and Functional Microbial Community in Sediments of a Basin-Fill Aquifer in Northern Utah

“…5). None of these sequences were related to any of the previously sequenced arrA genes from diverse environments, including West Bengal (25), Chesapeake Bay (24), and Crosswick Creek, Coastal Plain, NJ (28). This suggests a unique biogeographic distribution of DARB at the Cache Valley site ( Fig.…”

“…However, to obtain information about the potential As reduction function associated with these microorganisms requires the sequencing of the functional gene arrA. Previously, the arrA gene has been used to assess the diversity of DARB in a range of ecosystems, including water and sediments from Mono Lake and Searles Lake, CA (20)(21)(22), arsenic-contaminated aquifers in Cambodia (23,24) and West Bengal (25), estuarine sediments from Chesapeake Bay (26), and streambed sediments from the Inner Coastal Plain, NJ (27,28). However, information on the reduction of As V in relation to Fe reduction and the microbial community (both structural and functional) responsible for these reactions within the basin-fill environment of the Southwestern United States has not been reported.…”

Linking Genes to Microbial Biogeochemical Cycling: Lessons from Arsenic

“…This new energy-generating respiratory chain utilized the respiratory As(V) reductase, ArrAB, that reduce the less toxic As(V) to the more toxic and potentially more mobile As(III). 40,43,44 ArrAB is a heterodimer consisting of a large catalytic subunit (ArrA) and a small subunit (ArrB). 15,16 The arr operon also includes arrC , arrD , arrS , and arrR .…”

Characterization and transcription of arsenic respiration and resistance genes during in situ uranium bioremediation

“…The gene arrA, which encodes the a-subunit of the dissimilatory arsenate reductase protein (ArrA), has been used to document the presence of dissimilatory As(V)-reducing bacteria in a diversity of subsurface environments (Kulp et al, 2004(Kulp et al, , 2006Malasarn et al, 2004;Hollibaugh et al, 2006;Lear et al, 2007;Pederick et al, 2007). There are a number of previously described dissimilatory As(V)-reducing bacteria, such as Shewanella trabarsenatis ANA3 (Saltikov et al, 2003a;Saltikov and Newman, 2003b) and Sulfurospirillum barnesii, Sulfurospirillum arsenophilus (Stolz et al, 1999), Alkaliphilus oremlandii (Fisher et al, 2008), Bacillus arseniciselenatis (Blum et al, 1998), a Desulfosporosinus species (PerezJimenez et al, 2005) and Desulfotomaculum auripigmentum (Newman et al, 1997a, b).…”