Microbial communities at a gasworks site : a marker gene- and cultivation-based approach to explore anaerobic aromatic compound degradation

Environmental pollutants such as BTEX (benzene, toluene, ethylbenzene, o-, m-, p-xylene) and other aromatic compounds are frequently detected at gasworks sites. The diversity and functioning of aromatic compound-degrading bacteria (ACDB) was investigated in the groundwater of a former Thuringian gasworks site by 16S rRNA and bamA marker gene analysis as well as by enrichment cultures. Nitrate-reducing ACDB (Betaproteobacteria) dominated the anaerobic aquifer. In a highly contaminated area of the plume, nitrate-reducing ACDB co-occurred with obligate anaerobic sulfate- and/or CO2-reducing ACDB (Deltaproteobacteria and Firmicutes), indicating an area of oxygen and nitrate depletion in which biodegradation is assumed to occur with limited rates. To explore to possibility of bioremediation with nitrate, the role of several nitrate dependent ACDB was investigated in more detail: Members of the genus Azoarcus were key players in the degradation of toluene, ethylbenzene and other monoaromatic compounds. They outcompeted co-occurring ACDB, presumably by the excretion of nitrite. Organisms related to Georgfuchsia toluolica were less abundant in the aquifer and involved in the degradation of the particularly recalcitrant compound p-xylene. The chemolithoautotrophic, sulfur-oxidizing bacterium Sulfuritalea hydrogenivorans sk43H was found to have an overlooked role in nitrate dependent degradation of aromatic carboxylic compounds. Sulfuritalea-related bacteria were also highly abundant in the aquifer and involved in the degradation of p-alkylated aromatic carboxylates. The conducted experiments comprise the first systematic analysis of 16S rRNA and bamA sequences using environmental samples in combination with enrichment cultures. Results from both marker genes were largely consistent and an implementation of bamA-sequencing as routine diagnostic tool to assess redox processes relevant for bioremediation is suggested.