MINERALS MADE BY MICROBES THAT METABOLIZE ANTIMONY (SB) UNDER ANOXIC CONDITIONS

Microorganisms play key roles in the environmental cycling of metalloids and other elements. Bacteria are known to alter the oxidation state of various toxic metals and metalloids such as arsenic (As), selenium (Se), and antimony (Sb) and this, in turn alters the mobility, toxicity, cellular transport, and mineral formation of these elements.

In this study we examine biologically and chemically produced mineral phases of Sb produced under anoxic and reducing conditions. Antimony is a trace element commonly found associated with arsenic, but its environmental behavior and biochemistry are less well understood. We cultured and experimented with a Sb-reducing, novel bacterial strain isolated from contaminated mine sediments in Idaho. The cultures were amended with varying concentrations of aqueous Sb(V) (2mM, 1mM, 0.5mM, or 0.25mM). We monitored biological Sb(V)-reduction to Sb(III) along with abiotic reduction in killed control microcosms, and observed precipitate production for several days. The resulting mineral precipitates were dried, collected, and identified using X-ray Diffraction.

At high Sb(V) concentration (>2mM) the majority of precipitate in cultures and in abiotic conditions is chemically produced mopungite (Na[Sb(OH)₆), whereas only the biological precipitates contained smaller portions (~20%) of senarmontite (Sb₂O₃) which we interpret to be biologically precipitated. At lower concentrations (<0.5mM) the only identified precipitate in the bacterial cultures is a polymorph of senarmontite, valentinite. No precipitate was produced at low concentration in killed controls. These preliminary results suggest that senarmontite or valentinite precipitation will result from Sb(V) reduction to Sb(III) in anoxic settings. The polymorph senarmontite is only expected in environments that have abundant aqueous Sb(V) and is expected to co-precipitate with the Sb(V) mineral mopungite.