Investigation of catechol 2,3-dioxygenase and 16S rRNA gene diversity in hypoxic, petroleum hydrocarbon contaminated groundwater.

Detection of catechol 2,3-dioxygenase genes in aromatic hydrocarbon contaminated environments gives the opportunity to measure the diversity of bacteria involved in the degradation of the contaminants under aerobic conditions. In this study, we investigated the diversity and distribution of Comamonadaceae family (Betaproteobacteria) related catechol 2,3-dioxygenase genes, which belong to the I.2.C subfamily of extradiol dioxygenase genes. These catabolic genes encode enzymes supposed to function under hypoxic conditions as well, and may play a notable role in BTEX degradation in oxygen limited environments. Therefore, their diversity was analyzed in oxygen limited, petroleum hydrocarbon contaminated groundwater by terminal restriction fragment length polymorphism and cloning. Subfamily I.2.C related catechol 2,3-dioxygenase genes were detected in every investigated groundwater sample and a dynamic change was observed in the case of the structure of C23O gene possessing bacterial communities. To link the metabolic capability to the microbial structure, 16S rRNA gene-based clone libraries were generated and it was concluded that Betaproteobacteria were abundant in the bacterial communities of the contaminated samples. These results support the opinion that Betaproteobacteria may play a significant role in BTEX degradation under hypoxic conditions.