Study of mechanisms of selenite-reduction in gram positive bacteria

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Several bacterial strains were isolated from the rhizosphere of wheat crops in the northwestern region of Punjab, India. One of the strains, which reduced both selenate and selenite under aerobic conditions, was identified as Bacillus sp. NPT-1. The strain removed selenite in the medium within 24 h and produced amorphous selenium particles with an average particle size of 311 nm in diameter.To identify genes responsible for selenite reduction, mutant strains defective in the activity were generated by random insertion of the conjugative transposon Tn916 using Enterococcus faecalis CG110. Among the mutants obtained, 3 mutants contained a single insertion of Tn916, and their reduction activity was significantly decreased. One of the genes responsible for the loss of the function showed a high homology with a manganese catalase-like gene in Bacillus. An in vitro selenite-reduction study of the heterologously expressed gene suggested its function as a selenite reductase.