DNA-SIP of hypoxic toulene degraders. groundwater metagenome

The degradation of aromatic hydrocarbons in contaminated subsurface environments is often limited by the availability of oxygen. At zones of limited, but sustained oxygen supply, such as in the vicinity of groundwater monitoring wells, hypoxic degradation could have an important role and genes within the subfamily I.2.C extradiol dioxygenase (C23O) could be involved. In an oxygen-limited BTEX-contaminated shallow aquifer in Hungary stable isotope probing (SIP) incubation of site sediments with 13C7-toluene was performed under microoxic conditions. A combination of 16S rRNA gene amplicon sequencing and T-RFLP fingerprinting of C23O genes from SIP gradient fractions revealed the central role of degraders within the Rhodocyclaceae in hypoxic toluene degradation. The main assimilators of 13C label were identified as members of the genera Quatrionicoccus and Zoogloea, and a yet uncultured group of the Rhodocyclaceae. In contrast, well known aerobic degraders such as Pseudomonas and Pseudoxanthomonas spp. remained unlabelled in the microcosms.