One-year monitoring of meta-cleavage dioxygenase gene expression and microbial community dynamics reveals the relevance of subfamily I.2.C extradiol dioxygenases in hypoxic, BTEX-contaminated groundwater

Táncsics, András and Farkas, Milán and Szoboszlay, Sándor and Szabó, István and Kukolya, József and Vajna, Balázs and Benedek, Tibor and Kriszt, Balázs (2013) One-year monitoring of meta-cleavage dioxygenase gene expression and microbial community dynamics reveals the relevance of subfamily I.2.C extradiol dioxygenases in hypoxic, BTEX-contaminated groundwater. Systematic and Applied Microbiology, 36 (5). pp. 339-350.

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Abstract

Aromatic hydrocarbons including benzene, toluene, ethyl-benzene, and xylene (BTEX) are frequent contaminants of groundwater, the major resource of drinking water. Bioremediation is the only sustainable process to clean up these environments. Microbial degradation of BTEX-compounds occurs rapidly under aerobic conditions, but in subsurface environments the availability of oxygen is commonly restricted. Even so, the microaerobic degradation of aromatic compounds is still poorly understood. Hence, the dynamics of bacterial community and the expression of meta-cleavage dioxygenase genes, with particular emphasis on subfamily I.2.C extradiol dioxygenase genes, were assessed over a 13-month period in a hypoxic, aromatic hydrocarbon contaminated shallow groundwater by using sequence-aided terminal-restriction fragment length polymorphism (T-RFLP) and single-nucleotide primer extension (SNuPE) respectively. The bacterial 16S rRNA fingerprinting revealed the predominance of Rhodoferax, Azoarcus, Pseudomonas members and unknown bacteria related to Rhodocyclaceae. It was observed that mRNA transcripts of subfamily I.2.C extradiol dioxygenase genes were constantly detectable over the monitoring period, and the detected sequences clustered into six distinct clusters. In order to reveal changes in the expression of these clusters over the monitoring period we developed a SNuPE assay. This quasi fingerprinting of functional gene expression provided opportunity to link the investigated function to specific microbial populations. Results obtained can improve our understanding of aromatic hydrocarbon degradation under oxygen limitation and may benefit bioremediation research by demonstrating the usefulness of SNuPE for the monitoring of microbial populations involved in degradation process.

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