Project description:We report here a methanotroph, Methylotuvimicrobium buryatense 5GB1C, that consumes methane at 500ppm at rates several times higher than any previously published. Analyses of bioreactor-based performance and RNAseq based transcriptomics suggest that this superior ability to utilize low methane is based at least in part on an extremely low non-growth associated maintenance energy and on a 5-fold higher methane specific affinity than previous reports.
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.
Project description:Microbes that can recycle one-carbon (C1) greenhouse gases into fuels and chemicals are vital for the biosustainability of future industries. Acetogens are the most efficient known microbes for fixing carbon oxides CO2 and CO. Understanding proteome allocation is important for metabolic engineering as it dictates metabolic fitness. Here, we use absolute proteomics to quantify intracellular concentrations for >1,000 proteins in the model-acetogen Clostridium autoethanogenum grown on three gas mixtures. We detect prioritisation of proteome allocation for C1 fixation and significant expression of proteins involved in the production of acetate and ethanol as well as proteins with unclear functions. The data also revealed which isoenzymes are important. Integration of proteomic and metabolic flux data demonstrated that enzymes catalyse high fluxes with high concentrations and high in vivo catalytic rates. We show that flux throughput was dominantly controlled through enzyme catalytic rates rather than concentrations. Our work serves as a reference dataset and advances systems-level understanding and engineering of acetogens.
Project description:Microbes that can recycle one-carbon (C1) greenhouse gases into fuels and chemicals are vital for the biosustainability of future industries. Acetogens are the most efficient known microbes for fixing carbon oxides CO2 and CO. Understanding proteome allocation is important for metabolic engineering as it dictates metabolic fitness. Here, we use absolute proteomics to quantify intracellular concentrations for >1,000 proteins in the model-acetogen Clostridium autoethanogenum grown on three gas mixtures. We detect prioritisation of proteome allocation for C1 fixation and significant expression of proteins involved in the production of acetate and ethanol as well as proteins with unclear functions. The data also revealed which isoenzymes are important. Integration of proteomic and metabolic flux data demonstrated that enzymes catalyse high fluxes with high concentrations and high in vivo catalytic rates. We show that flux throughput was dominantly controlled through enzyme catalytic rates rather than concentrations. Our work serves as a reference dataset and advances systems-level understanding and engineering of acetogens.
Project description:Cyanobacteria fix atmospheric CO2 to biomass and through metabolic engineering can also act as photosynthetic cell factories for sustainable productions of fuels and chemicals. The Calvin cycle is the primary pathway for CO2 fixation in cyanobacteria, algae and C3 plants, and several studies have shown that overexpression of a cyanobacterial Calvin cycle enzyme, bifunctional sedoheptulose-1,7-bisphosphatase/fructose-1,6-bisphosphatase (hereafter BiBPase), enhances CO2 fixation in both plants and algae, although its impact on cyanobacteria has not yet been rigorously studied. Here, we show that overexpression of BiBPase enhanced growth, cell size, and photosynthetic O2 evolution of the cyanobacterium Synechococcus sp. PCC 7002 in an environment with elevated CO2 concentration. Biochemical analysis, immunodetection, and proteomic analysis revealed that overexpression of BiBPase considerably elevated the cellular activities of two rate-limiting enzymes in the Calvin cycle, namely ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) and aldolase, while it repressed several enzymes involved in the respiratory carbon metabolism (e.g. glycolysis and the oxidative pentose phosphate pathway) including glucose-6-phosphate dehydrogenase. Concomitantly, the content of glycogen was significantly reduced while the extracellular carbohydrate content increased. These results indicate that overexpression of BiBPase leads to global reprogramming of carbon metabolism in Synechococcus sp. PCC 7002, promoting photosynthetic carbon fixation and repressing the respiratory carbon catabolism, while altering carbohydrate partitioning.