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Abstract
The microbiota of the mammalian gut is widely recognized as a central regulator in maintaining host health. It is becoming increasingly clear that the metabolisms of intestinal microbes and their hosts are linked, and host-microbiome interactions are critical for health and well-being. Many studies have found that the efficacy or toxicity of xenobiotics can be modulated by the compositions of gut microbiota through microbial-dependent metabolic transformation. However, it is unclear how the gut microbiota and xenobiotics interact and whether these interactions are regulated via specific mechanisms. The nematode Caenorhabditis (C.) elegans and its bacterial diet have recently become a powerful interspecies model system to study host-mic interactions and the mechanisms involved. With two state-of-art instruments, COPAS Biosort and WMicrotracker, utilizing Escherichia (E.) coli K12-derived Keio collection, which comprises 3,985 strains each with a single non-essential gene deletion, this dissertation built up a 3-way high-throughput screening platform to elaborate the complex relationships between the host, microbes, and natural xenobiotic, aflatoxin B1 (AFB1), and identified the specific bacteria and genes involved in interactive metabolisms and metabolic pathways responsible for AFB1 toxicity. The screening revealed 73 significant mutant gene hits in E. coli that resulted in worm growth inhibition when compared to wild-type E. coli. Four genes (aceA, aceB, lpd, and pflB) involved in the pyruvate metabolism were then identified. The metabolomic analysis using LC-MS/MS showed significantly different AFB1 metabolites in C. elegans fed the four mutant strains than worms fed wild-type strain. To verify the role of the pyruvate pathway in response to AFB1 toxicity, we reconstructed the bacterial strains with triple-overexpression and triple-knockout on three gene hits (aceB, lpd, and pflB). The growth-promoting effect of overexpressed bacteria in pyk-1 mutant worms and the growth-inhibiting effect of triple-knockout bacteria in pdha-1 mutant worms indicated that pyruvate plays a vital role in modulating AFB1 toxicity in worms. The results were further confirmed by supplement with pyruvate fed with reconstructed bacterial strains. These results demonstrated that pyruvate metabolism is the critical pathway that modulates microbe-AFB1 interaction in the host.