Microbial Consortium Shifts Induced by Oxygen Amendment at Multiple MTBE and Benzene Sites

Eric Roberts, P.E., P.G.(Excalibur Group, LLC),Greg A. Davis and Debra C. McElroy (Microbial Insights), Francis X. Markert, P.E., P.G. (Excalibur Group, LLC),Ross Tabachow, PhD., P.E., (Excalibur Group, LLC)

 A previous study of in-situ stable isotope labeled probes applied at five different MTBE and benzene contaminated sites confirmed that the indigenous microbial communities at these sites actively metabolized the contaminants under both natural and oxygen enhanced conditions. While the rate of microbial degradation of the contaminants was shown to increase significantly under the oxygen-amended conditions, the particular microorganisms responding to the oxygen amendment could not be discerned from the gross categories of microbial community structures initially quantified using phospholipid fatty acids (PLFA) analysis. In this study, the authors examined the existing PLFA dataset in more detail to specifically identify shifts within the microbial populations, assess which microbial populations responded to the oxygen amendment at each site, and explore trends within the microbial consortium from site to site. Several consistent consortium shifts were observed in response to oxygen-enhanced conditions. The consistency of consortium shifts in response to the oxygen-enhanced conditions suggests these shifts could be used as a cost effective indicator of enhanced biodegradation performance.  At each of the five sites, Bio-Trap® samplers containing isotopically-labeled substrates were suspended and incubated in site monitoring wells for 30 days under a range of target dissolved oxygen (DO) concentrations (ambient, 6 ppm, and 12 ppm). The Bio-Trap samplers were amended with 13C-labeled MTBE or 13C-labeled benzene on beads which act as the sampling matrix. Retrieved Bio-Trap samplers were analyzed for PLFA to provide viable biomass and metabolic activity data. Broad phylogenic groups of microbes have different fatty acid profiles, making it possible to distinguish among them, and six major structural groups were initially identified at each of the sites. Detailed examination of the PLFA analysis completed under this study found that signature Proteobacterial biomarkers were observed to shift in relative abundance with oxygen amendment. Furthermore, the biomarkers that increased were shown to be the main uptake sources of the 13C-labeled substrate, indicating that the shift in biomarkers was due to an increased proportion of microorganisms that were degrading the 13C-labeled substrate. This pattern was observed at all five sites, suggesting that measurement of relative abundance of these Proteobacterial biomarkers could provide a useful tool for monitoring the microbial consortium during remediation. The authors believe standard PLFA analysis without 13C-labeled substrate could be a cost effective tool to monitor the relative proportions of these key biomarkers as indicators of ongoing enhanced biodegradation.  Only if the relative proportions of these biomarkers were observed to revert to background or other proportions would more costly analyses using 13C-labeled substrate be needed to determine whether DO amendments were no longer effectively stimulating bioremediation at the site.

Abstract K-034, in: Bruce M. Sass (Conference Chair), Remediation of Chlorinated and Recalcitrant Compounds—2008. Proceedings of the Sixth International Conference on Remediation of Chlorinated and Recalcitrant Compounds (Monterey,CA; May 2008). ISBN 1-57477-163-9, published by Battelle, Columbus, OH, www.battelle.org/chlorcon.