UC San Diego

The isolation and cultivation method of microorganisms has been explored to study morphology, physiology, genetics, and pathogenicity of organisms in detail. Pure cultured microorganisms provide us informative knowledge on the physiology of organisms but it has some limits in the examination of interactions of microorganisms with their microbial community. Coculture study has strong merits in that it helps us understand interactions between microorganisms and predict the phenotypic changes that might occur during the cultivation. The physiology of Moorella thermoacetica was examined when it was cocultured with six secondary organisms : Geobacter sulfurreducens, Thermotoga maritima, Clostridium ljungdhalii, Sporomusa ovata, Methanosarcina barkeri, and Methanococcus maripaludis. M. thermoacetica growth was enhanced only with supplementation of G. sulfurreducens cells. To interpret the cause of the amplified growth of M. thermoacetica, different components of G. sulfurreducens were examined. The metabolites were analyzed by mass spectrometer in order to find the compound responsible for the growth advantage of M. thermoacetica. From LCMS analysis, total 138 compounds were detected as metabolites of M. thermoacetica. The genetic profiles of M. thermoacetica and M. thermoacetica with filtered G. sulfurreducens media were analyzed. Detection of plasmid pJIR418 in Cmr transformants of M. thermoacetica was also performed by PCR after the extraction of plasmid. Single compound or genes responsible for the stimulation of growth of M. thermoacetica were unable to be identified. When M. thermoacetica was supplemented with G. sulfurreducens, the biomass was doubled but the hydrogen production was decreased. RNA sequencing result shows no significant change in hydrogenase activity between two samples, which indicates M. thermoacetica produces hydrogen and consumes hydrogen for respiration as well. The genes identified for the respiration, however, were not up-regulated with the supplementation of G. sulfurreducens. The results indicate that the secondary organisms have an impact on the proteomics or fluxomics level of M. thermoacetica