Bacillus selenitireducens MLS10
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This organism was isolated from Mono Lake, California (Switzer Blum et al., 1998). It is a low G+C (49%), Gram + arsenate-respirer. It is a haloalkaliphile, showing optimal growth at high salinity (24 - 60 g/L) and pH (8.5 - 10). It is the only well-described organism that can respire toxic selenite in addition to arsenate, nitrate, nitrite, TMAO, fumarate, and has some capacity for microaerophilic growth. Recently, it was found to be capable of respiring elemental sulfur, and can also reduce elemental selenium to selenide (Herbel et al., 2003). When grown on selenite, B. selenitireducens produces intracellular and extracellular nanoparticles of elemental selenium (Se(0) (Oremland et al., 2004). The respiratory arsenate-reductase of B. selenitireducens is membrane-associated and is a heterodimer of the DMSO family of Mo-containing enzymes (Afkar et al, 2003). There is significant sequence similarity of the catalytic subunit (ArrA) to ArrA from other phylogenetically unrelated species, however other aspects of the arr operon (e.g., number of genes encoding additional subunits, regulatory elements) may differ (Stolz et al., 2006).

Afkar, E., Lisak, J., Saltikov, C., Basu, P., Oremland, R.S., and Stolz, J.F. 2003. The respiratory arsenate reductase from Bacillus selenitireducens strain MLS10. FEMS Microbiol. Letts. 226:107-112

Herbel, M.J., Switzer Blum, J., Oremland, R.S., and Borglin, S.E., 2003. Reduction of elemental selenium to selenide: experiments with anoxic sediments and bacteria that respire Se-oxyanions. Geomicrobiol. J. 20:587-602.

Oremland, R.S., Herbel, M.J., Switzer Blum, J., Langley, S., Beveridge, T.J., Ajayan, P.M., Ellis, A.V., and Curran, S. 2004. Structural and spectral features of selenium nanospheres produced by Se-respiring bacteria. Appl. Environ. Microbiol. 70:52-60

Stolz, J.F., Basu, P., Santini, J.M., and Oremland, R.S. 2006. Selenium and arsenic in microbial metabolism. Annu. Rev. Microbiol. 60:107-130

Switzer Blum, J., A.B. Bindi, J. Buzzelli, J.F. Stolz, and R.S. Oremland. 1998. Bacillus arsenoselenatis sp. nov., and Bacillus selenitireducens sp. nov.: two haloalkaliphiles from Mono Lake, California, which respire oxyanions of selenium and arsenic. Arch. Microbiol. 171:19-30.