Physiological and molecular characterization of anaerobic benzene‐degrading mixed cultures

Summary Nine distinct anaerobic benzene‐degrading cultures were enriched from sediment samples from four different sites. These cultures used nitrate, sulphate or CO 2 as electron acceptors. The shortest doubling times were observed in nitrate‐reducing cultures, although cell yield was lowest in these cultures. The highest substrate concentration utilized and maximum absolute rates of benzene degraded (in µM day −1 ) were observed in methanogenic cultures. The microbial compositions of a methanogenic and nitrate‐reducing culture were determined from a clone library of 16S rRNA genes. Five Bacterial 16S rRNA sequences, one of which resembled a clone previously found in a sulphate‐reducing, benzene‐degrading culture and four Archaeal 16S rRNA sequences were identified in a methanogenic culture. Four Bacterial and no Archaeal 16S rRNA sequences were identified in a nitrate‐reducing culture. The relative abundance of the four nitrate‐reducing putative species was determined by slot blot hybridization. Two green sulphur bacteria together formed 52% of the clone library, but were found to be less than 4% of the culture by slot blot analysis. One of the cloned 16S rRNA gene sequences comprised 70% of the culture and was phylogenetically 93% similar to both Azoarcus and Dechloromonas species, which have been shown to degrade aromatic compounds, including benzene, under nitrate‐reducing conditions.