Bacterial diversity and aerobic biodegradation potential in a BTEX-contaminated aquifer

In order to gain insight into the community structure and the biodegradative potential of bacteria residing in a BTEX-contaminated field site, with benzene as main pollutant, an investigation strategy with a variety of cultivation-independent and -dependent approaches was undertaken. Based on 16S ribosomal DNA sequence analysis, sampling stations in the center of the pollution plume were found to be dominated by a bacterial consortium affiliated with various members of the class of Proteobacteria and Firmicutes, including different sporulating and non-sporulating sulfate-reducing bacteria and members of the genus Geobacter. Non-polluted samples retrieved from outside the plume revealed several phylotypes which were also observed in the centre of the plume. Bacterial sequences retrieved from the fringe of the plume were dominated by several genera of beta Proteobacteria subclass which were not associated with other phylotypes obtained in this study. All sampling stations were tested positive for catechol 2,3-dioxygenase genes, indicating the presence of microorganisms with the genetic potential degrading aromatic compounds via the meta-cleavage pathway. The groundwater system at the down-gradient edge of the plume was characterized, in contrast to all other sampling stations in the center and outside the plume, by high numbers of cultivable bacteria and cultivable aerobic benzene and toluene degraders. These findings are also in accordance with the investigations based on fluorescent in situ hybridization (FISH) with rRNA-targeted oligonucleotide probes, suggesting the presence of an actively benzene degrading bacterial community of beta Proteobacteria at the fringe of the pollution plume.