EXTRACELLULAR REDUCTION OF SELENITE BY A NOVEL MARINE PHOTOSYNTHETIC BACTERIUM

A novel purple nonsulfur bacterium strain NKPB030619, which has resist ance to over 5 mM selenite, was isolated from a marine environment. An initial concentration of 1.1 mM selenite, added to the medium, was de creased to under 0.05 mM within 5 days. The color of the cell suspensi on turned red within 2 days. The red coloration gradually decreased an d black precipitates appeared during 2 weeks of cultivation. Under the se conditions, two main types of deposit were formed extracellularly. These deposits were thought to contain red amorphous selenium and blac k vitreous selenium. The selenite reduction to elemental selenium in t his bacterium was induced by the introduction of light and L-malic aci d under anaerobic conditions. These results suggest that selenite redu ction is coupled with photosynthesis and L-malic acid can serve as the indirect electron donor for its reduction. Phylogenetic analysis base d on the 16S rDNA sequence showed that NKPB0360619 belongs to the alph a subdivision of Proteobacteria and is classified into the Rhodobacter species. The highest similarity of 86.2% was observed with R. sphaero ides.