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

Abstract

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.C 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.C catechol 2,3-dioxygenases were detected in considerable amounts in the contaminated samples by qPCR analysis, while activity of subfamily I.2.A, 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.

Unexpected Diversity and High Abundance of Putative Nitric Oxide Dismutase (Nod) Genes in Contaminated Aquifers and Wastewater Treatment Systems

“…The nod gene pools recovered from the two benzene, toluene, ethylbenzene, and xylene (BTEX)-impacted aquifers were strikingly different, possibly reflecting distinct contamination and redox scenarios at the sites (26)(27)(28). While the absolute abundance of the nod gene was one order of magnitude higher in Siklós than that in Flingern (Fig.…”

“…The samples used in this study were collected from various sites, as listed in Table 2. Siklós sediment samples were collected in April 2015 from the bottom of monitoring well ST2 in the center of a xylene plume in Siklós, Hungary (26,27), while Flingern sediments were taken by push-coring from the upper fringe of a toluene plume (6.4 m below ground) in Flingern, Düsseldorf, Germany, in September 2013 (28,37). Sediments were transported to the lab in cooling boxes and were then frozen at Ϫ20°C before DNA extraction.…”

Microbial communities in sea cucumber (Apostichopus japonicus) culture pond and the effects of environmental factors

“…According to previous studies, Proteobacteria was found effective in removing the organic pollutants in water, thus playing a role in water purification (Táncsics et al, 2012). Also, the abundance of Proteobacteria was correlated with nutrient content in water.…”

“…In water, the content of Proteobacteria and COD in YK was found significantly higher ( p < 0.05) than that in the other regions, suggesting that there was certain correlation between the relative abundance of Proteobacteria and the content of organic matters in pond water. According to previous studies, Proteobacteria was found effective in removing the organic pollutants in water, thus playing a role in water purification (Táncsics et al, ). Also, the abundance of Proteobacteria was correlated with nutrient content in water.…”

Microbial Toluene Removal in Hypoxic Model Constructed Wetlands Occurs Predominantly via the Ring Monooxygenation Pathway

“…Likewise, the catechol 2,3-dioxygenases encoded in the catabolic operons, together with this type of monooxygenase, have also been reported to perform efficiently under low-oxygen conditions (68). The appearance of genes encoding multicomponent monooxygenase and extradiol dioxygenases from the subfamily I.2.C type (18) has been detected in other hypoxic environments, indicating that these types of genes could have a relevant function in these type of systems, which has not been well studied or exploited yet (69,70).…”