Energy & redox fluxes in Lactobacillus reuteri DSM 17938 on different sugars
Sammanfattning: Under anaerobic condition the specific growth rate of Lactobacillus reuteri DSM 17938 on different sugars, was analyzed using spectrophotometry. Electron acceptor (fructose) supported cells to cope with poor energy recovery by re-oxidising the NADH, thus enabling ATP formation thru acetate production, while fermenting glucose via the phosphoketolase pathway (PKP) and simultaneously operating via Embden-Meyerhof pathway (EMP). The specific growth rate on glucose, maltose and sucrose was improved unquestionably in the presence of fructose. Analysis of the fermentation products showed in the fermentations without fructose produced relatively more ethanol than in all other cases studied so far with L. reuteri DSM 17938. It indicated that the enzyme pyruvate dehydrogenase (PDH) is active. It can be hypothesized that the particular growth environment (SD4 without electron acceptor) caused intracellular conditions that activated PDH. Comparison with the literature revealed that this enzyme is highly regulated on metabolic level by a number of metabolites. In short, this study displayed that the environmental conditions (anaerobic, pH 5.5) together with medium composition (SD4) had an effect of the fluxes through the two central carbon pathways in L. reuteri DSM 17938, which had no apparent effect on the energy and redox fluxes. Due to that ethanol could be produced via each pathway it made it impossible to estimate the flux in each pathway. Therefore, two extreme cases, regarding the variation in the cofactor formation flux ratio, RJ (ratio between the redox formation flux (JNADH+NADPH), and the energy carrier formation flux (JATP)), were investigated: PDH not active (SD4 media with e- acceptor) and PDH active (SD4 media without e- acceptor). The real case is somewhere between the two cases. Thus the results need verification and further experiments. Additionally the data obtained from osmotic potential measurements reflected the product formed during the fermentation and showed linear correlation between osmotic potential and optical density.
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