Extracellular reduction of selenite by a novel marine photosynthetic bacterium

Abstract

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

Isolation of Tellurite- and Selenite-Resistant Bacteria from Hydrothermal Vents of the Juan de Fuca Ridge in the Pacific Ocean

“…Multiple detoxification processes may occur during selenite and tellurite reduction by microorganisms because elemental Se and Te have been described as deposits in the cytoplasm, in the periplasm, and outside the cell (13,19,25,26,43,45,46,47,54,55,58). According to Tomei et al (47), particles containing elemental Se found outside cells are released by cell lysis, whereas Losi and Frankenberger (26) suggested that the reduction reaction occurs close to the membrane, possibly as a result of a membrane-associated reductase, and that the par- (19) speculated that a vesicular mechanism of Se excretion occurs in Rhodospirillum rubrum.…”

Ecology and Biotechnology of Selenium-Respiring Bacteria

“…15) The levels of reduced thioredoxin [Trx(SH) 2 ] and thioredoxin reductase (93) were increased in E. coli cells grown in medium containing SeO 3 2Ϫ . The reduced thioredoxin reacts with selenodiglutathione and forms oxidized thioredoxin (Trx-S 2 ), reduced glutathione, and selenopersulfide anion.…”

Genetic and Biochemical Evidence for the Involvement of a Molybdenum-Dependent Enzyme in One of the Selenite Reduction Pathways ofRhodobacter sphaeroidesf. sp.denitrificansIL106

“…Depending upon the species, this process is generally followed by intracellular sequestration of the insoluble metallic form in the cytoplasm (11,23), which is of great interest for bioremediation. Excretion of Se 0 outside the cell has also been described (12,41). In a few species of bacteria, selenate and selenite act as electron acceptors in an anaerobic form of respiration (16,33,34), whereas for most of the microorganisms studied so far, reduction of selenium oxyanions is not a bioenergetic process.…”