Evaluating degradation genes in a culture obtained from a contaminated solvent bioreactor

The objective of the study was to optimize the degradation of chlorinated solvents by cultivating the indigenous microbial community from in situ bioreactor (Trench 1) and to investigate which electron donors (acetate, lactate, pyruvate) would increase the degradation rate in those cultures. This investigation attempted to help optimize effectiveness and efficiency of an in situ mulch/gravel bioreactor currently implemented at Camp Stanley. This research used general microbiology, molecular biology, and analytical methods to evaluate the biodegradation in the cultures. Techniques used were polymerase chain reaction (PCR) of universal and specific Dehalococcoides dehalogenase genes (16S rDNA, DHC 16S rDNA, and tceA ) along with gas chromatography-flame ionization detector (GC-FID) to evaluate the chlorinated solvents (PCE, TCE, cis-DCE, VC) disappearance. The cultures analyzed indicated the importance of a steady concentration of electron donor and acceptor to maintain biodegradation; however if too much donor was provided it would inhibit the desired growth of the Dehalococcoides populations. The GC data suggested that biological processes may not be dominating the degradation process due to the lack of oscillation and accumulation of the solvents in the cultures. The solvents in the cultures degraded at the same rate and did not accumulate with time thus suggesting abiotic processes are more likely degrading the solvents. The geochemistry and microbiology of the mulch/gravel bioreactor technologies are more complex and dynamic than previously thought. Future research needs to examine both the abiotic and biotic processes to better understand how to optimize and maintain the degradation potential in this technology.