Anaerobic utilization of alkylbenzenes and n-alkanes from crude oil in an enrichment culture of denitrifying bacteria affiliating with the beta-subclass of Proteobacteria

Denitrifying bacteria were enriched from freshwater sediment with added nit rate as electron acceptor and crude oil as the only source of organic subst rates. The enrichment cultures were used as laboratory model systems for st udying the degradative potential of denitrifying bacteria with respect to c rude oil constituents, and the phylogenetic affiliation of denitrifiers tha t are selectively enriched with crude oil. The enrichment culture exhibited two distinct growth phases. During the first phase, bacteria grew homogene ously in the aqueous phase, while various C-1-C-3 alkylbenzenes, but no alk anes, were utilized from the crude oil. During the second phase, bacteria a lso grew that formed aggregates, adhered to the crude oil layer and emulsif ied the oil, while utilization of n-alkanes (C-5 to C-12) from the crude oi l was observed, During growth, several alkylbenzoates accumulated in the aq ueous phase, which were presumably formed from alkylbenzenes. Application o f a newly designed, fluorescently labelled 16S rRNA-targeted oligonucleotid e probe specific for the Azoarcus/Thauera group within the P-subclass of Pr oteobacteria revealed that the majority of the enriched denitrifiers affili ated with this phylogenetic group.