Degradation of aromatic compounds coupled to selenate reduction

The degradation of a range of aromatic compounds under selenate-reducing conditions was examined. Enrichment cultures were initiated with a 10% sediment slurry from the Arthur Kill, an intertidal strait in the New York/New Jersey harbor, and from the Kesterson Reservoir, California, with selenate as the sole electron acceptor. After repeated feeding, activity was maintained with either benzoate, 3-hydroxybenzoate, or 4-hydroxybenzoate as the sole carbon substrate. Degradation of the benzoic acid derivatives did not occur without the addition of selenate, or in sterile controls, indicating that substrate utilization was dependent on selenate reduction. Degradation of each of these aromatic compounds was coupled stoichiometrically to the reduction of selenate to selenite. Two selenate-reducing bacterial strains that utilized 4-hydroxybenzoate as a carbon source were isolated from the Arthur Kill and the Kesterson Reservoir, respectively. Based on analysis of their 16S rRNA gene sequences these isolates were 98.3% similar to one another, but distinct from other known Se(VI)-reducing bacteria. Phylogenetic analysis indicated that they were affiliated with the gamma subgroup of the Proteobacteria, with uncultured sulfur-oxidizing symbionts as their closest neighbors.