A Systems-Level Investigation of the Metabolism of Dehalococcoides mccartyi and the Associated Microbial Community

摘要

Dehalococcoides mccartyi are a group of strictly anaerobic bacteria important for the detoxification of man-made chloro-organic solvents, most of which are ubiquitous, persistent, and often carcinogenic ground water pollutants. These bacteria exclusively conserve energy for growth from a pollutant detoxification reaction through a novel metabolic process termed organohalide respiration. However, this energy harnessing process is not well elucidated at the level of D. mccartyi metabolism. Also, the underlying reasons behind their robust and rapid growth in mixed consortia as compared to their slow and inefficient growth in pure isolates are unknown. To obtain better insight on D. mccartyi physiology and metabolism, a detailed pan-genome-scale constraint-based mathematical model of metabolism was developed. The model highlighted the energy-starved nature of these bacteria, which probably is linked to their slow growth in isolates. The model also provided a useful framework for subsequent analysis and visualization of high-throughput transcriptomic data of D. mccartyi . Apart from confirming expression of the majority genes of these bacteria, this analysis helped review the annotations of metabolic genes. Revised annotations of two such metabolic genes --- NADP+-isocitrate dehydrogenase and phosphomannose isomerase --- were then experimentally verified. Finally, growth experiments were performed with a D. mccartyi -containing anaerobic mixed enrichment culture to explore the effects of exogenous vitamin omission from the growth medium on D. mccartyi and the associated microbial community. The experiments showed how nutritional requirements of these bacteria changed the composition and dynamics of their associated microbial community. Overall, a systems-level approach was used in this research to obtain a fundamental and critical understanding of the metabolism and physiology of D. mccartyi in isolates, as well as in microbial communities they naturally inhabit. The results presented in this thesis, therefore, will help design effective strategies for future bioremediation efforts by D. mccartyi.