Stable isotope profiling of ETBE degraders

A limited number of microorganisms have been identified with the capability to degrade ethyl tert-butyl ether (ETBE) in the environment. Knowledge of the identify and distribution of ETBE-degrading microorganisms is important for the implementation of management measures such as natural attenuation and bioremediation at ETBE-release sites. In this study, DNA-stable isotope probing (SIP) was used to identify microorganisms able to aerobically degrade 13C-labelled ETBE in laboratory microcosms constructed with groundwater and aquifer material from an ETBE-release site. Microorganisms in the Class ?-proteobacteria, Order ß-proteobacteriales, Family Burkholderiaceae, and classified as Methylibium, Rhodoferax and Leptothrix, respectively, were identified as primary ETBE degraders. Comparisons with ETBE-responsive microorganisms (those which increased in abundance after addition of ETBE), identified by high-throughput sequencing of microcosms established from the same site, showed that only a small proportion of the ETBE-responsive organisms were primary degraders as determined by SIP. ETBE degraders were taxonomically related to microorganisms able to degrade gasoline components, but not ETBE, implying that this functionality results from horizontal gene transfer of the eth gene cluster within the microbial community. These ETBE degraders could also be identified at ETBE-release sites, but at low relative abundance and generally only in those sites from which the microcosms had been established. Horizontal gene transfer may play an important role in the acquisition of ETBE-degrading capability within aquifer microbial communities at ETBE-release sites.