ANAEROBIC DEGRADATION OF ETHYLBENZENE AND OTHER AROMATIC-HYDROCARBONSBY NEW DENITRIFYING BACTERIA

Anaerobic degradation of alkylbenzenes with side chains longer than th at of toluene was studied in freshwater mud samples in the presence of nitrate. Two new denitrifying strains, EbN1 and PbN1, were isolated o n ethylbenzene and n-propylbenzene, respectively. For comparison, two further denitrifying strains, ToN1 and mXyN1, were isolated from the s ame mud with toluene and m-xylene, respectively. Sequencing of 16S rDN A revealed a close relationship of the new isolates to Thauera selenat is. The strains exhibited different specific capacities for degradatio n of alkylbenzenes. In addition to ethylbenzene, strain EbN1 utilized toluene, but not propylbenzene. In contrast, propylbenzene-degrading s train PbN1 did not grow on toluene, but was able to utilize ethylbenze ne. Strain ToN1 used toluene as the only hydrocarbon substrate, wherea s strain mXyN1 utilized both toluene and m-xylene. Measurement of the degradation balance demonstrated complete oxidation of ethylbenzene to CO2 by strain EbN1. Further characteristic substrates of strains EbN1 and PbN1 were 1-phenylethanol and acetophenone. In contrast to the ot her isolates, strain mXyN1 did not grow on benzyl alcohol. Benzyl alco hol (also m-methylbenzyl alcohol) was even a specific inhibitor of tol uene and m-xylene utilization by strain mXyN1. None of the strains was able to grow on any of the alkylbenzenes with oxygen as electron acce ptor. However, polar aromatic compounds such as benzoate were utilized under both oxic and anoxic conditions. All four isolates grew anaerob ically on crude oil. Gas chromatographic analysis of crude oil after g rowth of strain ToN1 revealed specific depletion of toluene.