Anaerobic oxidation of o-xylene, m-xylene, and homologous alkylbenzenes bynew types of sulfate-reducing bacteria

Various alkylbenzenes were depleted during growth of an anaerobic, sulfate- reducing enrichment culture with crude oil as the only source of organic su bstrates. From this culture, two new types of mesophilic, rod-shaped sulfat e-reducing bacteria, strains oXyS1 and mXyS1, were isolated with o-xylene a nd m-xylene, respectively, as organic substrates. Sequence analyses of 16S rRNA genes revealed that the isolates affiliated with known completely oxid izing sulfate-reducing bacteria of the delta subclass of the class Proteoba cteria. Strain oXyS1 showed the highest similarities to Desulfobacterium ce tonicum and Desulfosarcina variabilis (similarity values, 98.4 and 98.7%, r espectively). Strain mXyS1 was less closely related to known species, the c losest relative being Desulfococcus multivorans (similarity value, 86.9%). Complete mineralization of o-xylene and m-xylene was demonstrated in quanti tative growth experiments. Strain oXyS1 was able to utilize toluene, o-ethy ltoluene, benzoate, and o-methylbenzoate in addition to o-xylene. Strain mX yS1 oxidized toluene, m-ethyltoluene, m-isoproyltoluene, benzoate, and m-me thylbenzoate in addition to m-xylene. Strain oXyS1 did not utilize m-alkylt oluenes, whereas strain mXyS1 did not utilize o-alkyltoluenes. Like the enr ichment culture, both isolates grew anaerobically on crude oil with concomi tant reduction of sulfate to sulfide.