ISOLATION AND CHARACTERIZATION OF A NOVEL TOLUENE-DEGRADING, SULFATE-REDUCING BACTERIUM

A novel sulfate-reducing bacterium isolated from fuel-contaminated sub surface soil, strain PRTOL1, mineralizes toluene as the sole electron donor and carbon source under strictly anaerobic conditions, The miner alization of 80% of toluene carbon to CO2 was demonstrated in experime nts with [ring-U-C-14]toluene; 15% of toluene carbon was converted to biomass and nonvolatile metabolic by-products, primarily the former, T he observed stoichiometric ratio of moles of sulfate consumed per mole of toluene consumed was consistent with the theoretical ratio for min eralization of toluene coupled with the reduction of sulfate to hydrog en sulfide, Strain PRTOL1 also transforms o- and p-xylene to metabolic products when grown with toluene. However, xylene transformation by P RTOL1 is slow relative to toluene degradation and cannot be sustained over time, Stable isotope-labeled substrates were used in conjunction, vith gas chromatography-mass spectrometry to investigate the by-produc ts of toluene and xylene metabolism, The predominant by-products from toluene, o-xylene, and p-xylene were benzylsuccinic acid, (2-methylben zyl)succinic acid, and 4-methylbenzoic acid (or p-toluic acid), respec tively, Metabolic by-products accounted for nearly all of the o-xylene consumed, Enzyme assays indicated that acetyl coenzyme A oxidation pr oceeded via the carbon monoxide dehydrogenase pathway. Compared with t he only other reported toluene-degrading, sulfate-reducing bacterium, strain PRTOL1 is distinct in that it has a novel 16S rRNA gene sequenc e and was derived from a freshwater rather than marine environment.