ARSC GENE EXPRESSION DURING MICROBIOLOGICAL SB(V) REDUCTION IN A HIGHLY SB- AND AS-RESISTANT BACTERIAL ISOLATE

The metalloids arsenic (As) and antimony (Sb), owing to similar chemical speciation and bond coordination, are both strongly chalcophilic toxic elements that most commonly occur in association with hydrothermal ore deposits and geothermal systems. The environmental mobility and toxicity of both elements is directly controlled by microbiological biotransformations, which have direct implications for responses aimed at managing As and/or Sb contaminated sites. The oxidized chemical species of these elements, As(V) and Sb(V), have been shown to serve as electron acceptors for microbial respiration under anoxic conditions, and numerous studies have also demonstrated that As(V) reduction to As(III) can also serve as a detoxification strategy for numerous phylogenetically diverse prokaryotes. Comparatively few studies have been directed toward the isolation and characterization of bacteria from natural settings that reduce Sb(V), and no previous studies have reported an analogous detoxification mechanism which involves enzymatic Sb(V) reduction. We have isolated a robust Sb-resistant and Sb(V)-reducing bacterium (strain JABI-1) from lake sediments collected from Warner Valley, OR. Strain JABI-1 can grow by fermenting amino acids in the presence of notably high Sb concentrations (up to 15mM) while reducing Sb(V) to Sb(III) and driving the precipitation of amorphous Sb₂O₃ (senarmontite), or alternately Sb₂S₃ (stibnite) when sulfide is present. This organism is also highly As-resistant and possesses the arsC gene which encodes for reductive As(V) resistance. Strain JABI-1 did not attain higher cell density with the presence of either Sb or As compared to in their absence, suggesting that the observed reduction is a detoxification strategy rather than a respiratory process. PCR amplification of arsC gene products demonstrated that this gene is expressed during growth of JABI-1 in the presence of both Sb(V) and As(V), providing the first evidence that the arsC gene may also confer resistance and detoxification pathways for Sb. This report adds to the current knowledge concerning microbiological interactions with Sb, and provides new evidence suggesting arsC, and possibly other genes that function to reduce As, may also be expressed and function analogously with Sb.