Microbial community in a trichloroethylene contaminated aquifer during toluene stimulated bioremediation.

摘要

Trichloroethylene (TCE), a common groundwater pollutant, is a major problem facing communities throughout the world. This widespread occurrence has created public demand for technologies to remediate aquifers contaminated with TCE. One such in situ technique is the phenol or toluene stimulated co-oxidation of WE and its dechlorination products. This technique is dependent on the capability of the intrinsic microbial population to produce oxygenases that degrade these chlorinated solvents given the appropriate stimulating conditions. In this work, I evaluated microbial community response to a field test of toluene-stimulated WE degradation implemented by a Stanford research team at Edwards Air Force Base (AFB). High-throughput sequencing and analysis of 16S rRNA gene libraries from filtered monitoring well water showed that populations taken 1 month and 3 months after toluene additions were statistically different from those found before toluene addition. Furthermore, communities near and down-gradient from the bio-treatment well were different from those up-gradient to the bio-treatment wells. The major trends noted were a decline in the Pseudomonas populations and an increase in Sphingomonas and eventually Legionella populations after toluene feeding. In order to determine the presence of toluene-degrading populations and to determine whether they co-oxidized TCE, I isolated and characterized dominant populations from the site. While some showed a low level of toluene consumption, none produced rapid growth on toluene and none oxidized TCE. Since both toluene and TCE were removed in the field test, the lack of toluene-degraders in the monitoring wells must be due to the fact that the toluene degraders had not yet reached these wells or the bacteria found there were not the ones oxidizing toluene.;Because of the Bio-Enhanced In-Well Vapor Stripping (BEHIVS) System used at Edwards AFB, I determined if bacteria in the Burkholderia cepacia complex (Bcc), were present. This group of opportunistic human pathogens, especially in cystic fibrosis (CF) patients, lives in soil and some grow on toluene. High-throughput 16S rRNA sequencing, isolation and characterization of colonies, and screening larger populations by hybridization with a Bcc specific probe revealed no such populations. But since members of the Bcc can be agents for bioremediation and because the clinical and environmental strains cannot be distinguished, I explored the different patterns of aromatic substrate use between clinical and environmental strains. Cluster analysis indicated that aromatic use by isolates from the environment was much higher than from the clinic, but that no set of one or a few substrates could reliably distinguish an environmental strain from a CF-lung colonizing strain.