Quantification of Subfamily I.2.C Catechol 2,3-Dioxygenase mRNA Transcripts in Groundwater Samples of an Oxygen-Limited BTEX-Contaminated Site

Low dissolved oxygen concentration of subsurface environments is a limiting factor for microbial aromatic hydrocarbon degradation, and to date, there are only a limited number of available reports on functional genes and microbes that take part in the degradation of aromatic hydrocarbons under hypoxic conditions. Recent discoveries shed light on the prevalence of subfamily I.2.0 catechol 2,3-dioxygenases in petroleum hydrocarbon contaminated hypoxic groundwaters, and their considerable environmental importance was suggested. Here, we report on a Hungarian aromatic hydrocarbon (methyl-substituted benzene derivatives, mostly xylenes) contaminated site where we investigated this presumption. Groundwater samples were taken from the center and the edge of the contaminant plume and beyond the plume. mRNA transcripts of subfamily I.2.0 catechol 2,3-dioxygenases were detected in considerable amounts in the contaminated samples by qPCR analysis, while activity of subfamily I.2.A0 which includes the largest group of extradiol dioxygenases described by culture-dependent studies and thought to be widely distributed in BTEX-contaminated environments, was not observed. Bacterial community structure analyses showed the predominance of genus Rhodoferax related species in the contaminated samples.