Production of two morphologically different antimony trioxides by a novel antimonate-reducing bacterium, Geobacter sp. SVR

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 ?m. Strain SVR removed 96% of dissolved Sb as the precipitates. An X-ray diffraction analysis indicated that the microcrystals were the orthorhombic Sb trioxide (Sb2O3), 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 Sb2O3 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.

Automated summary

Strain SVR, a dissimilatory antimonate-reducing bacterium, was isolated from soil and demonstrated the ability to reduce Sb(V) to precipitates. X-ray diffraction analysis revealed the precipitates to be Sb2O3, known as valentinite, with the bacterium able to form two different crystalline Sb2O3 structures under different pH conditions.