DISSIMILATORY ARSENATE AND SULFATE REDUCTION IN DESULFOTOMACULUM-AURIPIGMENTUM SP. NOV

A newly discovered arsenate-reducing bacterium, strain OREX-4, differe d significantly from strains MIT-13 and SES-3, the previously describe d arsenate-reducing isolates, which grew on nitrate but not on sulfate . In contrast, strain OREX-4 did not respire nitrate but grew on lacta te, with either arsenate or sulfate serving as the electron acceptor, and even preferred arsenate. Both arsenate and sulfate reduction were inhibited by molybdate. Strain OREX-4, a gram-positive bacterium with a hexagonal S-layer on its cell wall, metabolized compounds commonly u sed by sulfate reducers. Scorodite (FeAsO(4)2 . H2O) an arsenate-conta ining mineral, provided micromolar concentrations of arsenate that sup ported cell growth, Physiologically and phylogenetically, strain OREX- 4 was far-removed from strains MIT-13 rind SES-3: strain OREX-4 grew o n different electron donors and electron acceptors, and fell within th e gram-positive group of the Bacteria, whereas MIT-13 and SES-3 fell t ogether in the epsilon-subdivision of the Proteobacteria. Together, th ese results suggest that organisms spread among diverse bacterial phyl a can use arsenate as a terminal electron acceptor, and that dissimila tory arsenate reduction might occur in the sulfidogenic zone at arsena te concentrations of environmental interest. 16S rRNA sequence analysi s Indicated that strain OREX-4 is a new species of the genus Desulfoto maculum, and accordingly, the name Desulfotomaculum auripigmentum is p roposed.