Project 4: Adaptation of Subsurface Microbial Biofilm Communities in Response to Chemical Stressors

Principal Investigators: Paul Bishop, Nancy G. Love and Ann Stevens (University of Cincinnati and Virginia Polytechnic Institute and State University)

Collaborator: IT Corporation

Effective restoration of contaminated subsurface environments requires a thorough understanding of how the biota in natural systems is structured and functions. A substantial effort has been put forth over the past few decades to improve our understanding of catabolic biodegradative processes, which play a critical role in the restoration of environments that have been contaminated by hazardous wastes. However, if we are to restore ecosystems to a natural state, it is necessary to develop a more complete conceptual model of how microbial communities are structured and function both during the remediation process and after it is complete. An important component of this understanding involves moving beyond studying microbial catabolism and toward other metabolic processes that play a critical role in defining the structure and function of microbial communities that are exposed to hazardous wastes. Microorganisms have evolved mechanisms that either protect the cell or remediate cell damage due to the presence of toxic chemicals (stressors) at sublethal concentrations. The structure and function of microbial biofilm communities, which are exposed to chemical stressors over long time periods, are influenced through the activation of selected stress responses. We propose to study the short and long-term impact of two model electrophilic hazardous chemicals (pentachlorophenol (PCP) and cadmium) on the structure and function of aerobic biofilm communities such as those existing in contaminated subsurface environments. We will focus on studying a specific stress response, the glutathione-gated potassium efflux (GGKE) system, which is activated in response to electrophilic chemical stressors. The matrix of environmentally-relevant chemical stressors has been selected for this study so that the relative roles of catabolism versus the GGKE system on biofilm community adaptation during restoration of contaminated sites can be determined. Biofilm structures will be characterized by using microelectrodes to follow important chemical gradients within the biofilms, and fluorescent in situ hybridization (FISH) coupled with confocal laser scanning microscopy (CLSM) to track the location and activity of selected microorganisms. Biofilm function will be characterized by monitoring the fate of the chemical stressors (catabolism or abiotic sorption) and the activation of the GGKE stress mechanism that responds to electrophilic chemical stressors. The impact of this work will help improve our understanding of how subsurface biofilm communities respond to chemical stressors that are likely to be present at hazardous waste sites. Ultimately, these results can be used to determine more effective ways to insure proper environmental conditions are present for successful soil bioremediation.