A novel n-alkane-degrading bacterium as a minor member of p-xylene-degrading sulfate-reducing consortium.

A p-xylene-degrading, sulfate-reducing enrichment culture was characterized by analyzing the response of its members to changes in the available substrate. The culture was inoculated into media containing other substrates, resulting in the establishment of benzoate-, acetate-, and lactate-utilizing enrichment cultures. PCR-denaturing gradient gel electrophoresis (DGGE) analysis of the enriched cultures targeting 16S rRNA genes showed quite simple band patterns. The predominant band from the benzoate-utilizing enrichment culture was identical to that from the original enrichment culture utilizing p-xylene. A single, dominant DGGE band was observed in common from the acetate- and lactate-utilizing enrichment cultures. A novel sulfate-reducing bacterium, strain PL12, was isolated from the lactate-utilizing enrichment culture. The 16S rRNA gene sequence of strain PL12 was identical to that of the dominant DGGE band in the acetate- and lactate-utilizing enrichment cultures and distinct from the dominant sequences in the original p-xylene-degrading and benzoate-utilizing enrichment cultures. Phylogenetic analysis of the 16S rRNA gene sequences showed that the isolate belonged to the family Desulfobacteraceae in the class Deltaproteobacteria. The isolated strain PL12 could utilize n-hexane and n-decane as substrates, but could not utilize benzoate, p-xylene and other aromatic hydrocarbons. These results suggest that the p-xylene degradation observed in the original enrichment culture was performed by the dominant bacterium corresponding to DGGE band pXy-K-13 (Nakagawa et al. 2008). The novel strain PL12 might have been utilizing metabolites of p-xylene.