Project description:The bacteria that grow on methane aerobically (methanotrophs) support populations of non-methanotrophs in the natural environment by excreting methane-derived carbon. One group of excreted compounds are short-chain organic acids, generated in highest abundance when cultures are grown under O2-starvation. We examined this O2-starvation condition in the methanotroph Methylomicrobium buryatense 5GB1C . Under prolonged O2-starvation in a closed vial, this methanotroph increases the amount of acetate excreted about 10-fold, but the formate, lactate, and succinate excreted do not respond to this culture condition. In bioreactor cultures, the amount of each excreted product is similar across a range of growth rates and limiting substrates, including O2-limitation. A set of mutants were generated in genes predicted to be involved in generating or regulating excretion of these compounds and tested for growth defects, and changes in excretion products. The phenotypes and associated metabolic flux modeling suggested that in M. buryatense 5GB1C, formate and acetate are excreted in response to redox imbalance, and the resulting metabolic state represents a combination of fermentation and respiration metabolism.
Project description:Methylomicrobium buryatense 5GB1 is an obligate methylotroph, which grows on methane or methanol with similar growth rates. Core metabolic pathways are similar on both substrates, but recent studies of methane metabolism suggest that growth on methanol might have significant differences from growth on methane. In this study, both a targeted metabolomics approach as well as a 13C tracer approach have been taken to understand core carbon metabolism in M. buryatense 5GB1 during methanol growth, to determine whether such differences occur. Targeted metabolomics analyses were performed on both methane and methanol cultures to identify metabolic nodes with altered fluxes. Several key metabolites showed significant differences in pool size. Noticeably, 2-keto-3-deoxy-6-phosphogluconate (KDPG) showed much larger pools under methanol culture, suggesting the Entner-Doudoroff (ED) pathway was more active. Intermediates in other parts of metabolism also showed differences in pool sizes under methanol growth. A systematic shift of active core metabolism is proposed to explain the changes. In order to distinguish flux partition differences at the C3-C4 node, 13C tracer analysis was also applied to methanol-grown cultures. Using the experimental results as constraints, we applied flux balance analysis to determine the metabolic flux phenotype of M. buryatense 5GB1 growing on methanol. The resulting new insights into core metabolism of this methanotroph provide an improved basis for future strain design.
