A Rhodococcus species that thrives on medium saturated with liquid benzene

A bacterium isolated from a contaminated site in Sydney, Australia, utilized benzene in the liquid phase as a sole carbon source at levels toxic to other micro-organisms. The organism was a short Gram-positive rod which grew at 6% NaCl, 0-37 degrees C and pH 2-10. Biochemical tests, fatty acid analysis, and 16S rDNA sequencing identified the organism as a member of the genus Rhodococcus. Vapour-phase addition of benzene to the medium in batch and continuous systems resulted in initial concentrations averaging 200 p.p.m. Under these conditions, 95% of the benzene was degraded. In separate experiments, medium spiked with liquid benzene resulted in concentrations of up to 2789 p.p.m. and supported good growth of the organism. To confirm utilization of benzene at levels known to be toxic to other micro-organisms, continuous cultures were used; benzene added at 2% (v/v) per day resulted in growth and 89% degradation, which was maintained for more than 30 d. Rhodococcus sp. strain 33 appears to be the only organism known that can grow at these levels of benzene.