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 3% similar to both Azoarcus and Dechloromonas species, which have been shown to degrade aromatic compounds, including benzene, under nitrate-reducing conditions.
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