The optimization of Dehalococcoides-based bioremediation systems to treat trichloroethene (TCE)-contaminated Superfund sites relies upon knowledge-intensive understanding of complex microbial interactions that shape the structural and functional robustness of TCE-dechlorinating microbial communities exposed to a variety of geochemical conditions. Previous studies have shown that varied geochemical parameters, such as decreased pH or the presence of alternative terminal electron acceptors can result in incomplete dechlorination. We propose to use a combination of molecular, biochemical and analytical tools to evaluate interactions within sustainable and defined multi-strain microbial TCE- dechlorinating consortia in continuous-flow chemostats to study community interactions and the effects of biogeochemical conditions on dechlorination activity. Specifically, we propose to analyze community-level transcriptomics, intercellular metabolomics, and advanced Random Matrix Theory network analysis to understand the impact of geochemical stresses to the TCE-dechlorinating consortia. This project seeks to deliver a fundamental understanding of networked gene regulations and metabolite exchanges that impact anaerobic Dehalococcoides- containing microbial communities and control their TCE dechlorination capabilities. In the proposed work, a variety of environmentally-relevant geochemical stresses will be investigated including pH, salinity and the introduction of potential competitive electron acceptors to the system (e.g., sulfate ions). Effects of these geochemical stresses will be monitored and tracked through the exchanged metabolites, cellular processes and genetic regulations occurred amongst the interactive and interdependent populations in dechlorinating consortia. The generated knowledge will lead to an improved ability to design and optimize proactive engineering solutions to decrease the time and cost associated with successful groundwater bioremediation. The specific objectives to be investigated in this proposed study are, 1. Construct sustainable TCE-dechlorinating microbial consortia with multiple defined microbial species that represent the essential functions within robust TCE-dechlorinating communities, and establish their sustained growth in chemostats. 2. Identify the physiological changes, genetic regulatory changes, and the intercellular metabolic changes that occur in the TCE-dechlorinating consortia in response to changes in biogeochemical conditions, such as pH, salinity, and the presence of alternative electron acceptors. Metatranscriptomics and metabolomics analyses will be used to obtain a systems-level understanding of the complex responses of the consortia to geochemical stresses. 3. Establish correlations among biogeochemical conditions, microbial genetic regulations and metabolic interactions in order to elucidate the networked interactions among the members of the consortia that respond to various biogeochemical conditions. The results will be used to investigate stimulation or augmentation strategies that can stabilize the functions of dechlorination communities under changing geochemical conditions.