The products and pathways of glucose catabolism in Herpetomonas muscarum ingenoplastis and Herpetomonas muscarum muscarum

The products and pathways of glucose catabolism in the insect trypanosomatids Herpetomonas muscarum ingenoplastis and Herpetomonas muscarum muscarum have been studied with the aim of elucidating how both organisms are able to proliferate well under aerobic and anaerobic conditions. When incubated in medium containing glucose as the only exogenous carbon source, catabolism was found to be fermentative in both cases. Acetate was a major product of both organisms while H. m. ingenoplastis produced more ethanol and propionate and less succinate than H. m. muscarum. Ethanol production by H. m. ingenoplastis decreased both under anaerobic conditions and in the presence of elevated CO2 concentrations, whereas succinate and propionate release by this organism were greater in high CO2 and anoxia, respectively. Succinate production by H. m. muscarum was greatest under anaerobic conditions in elevated CO2, whereas propionate was only a minor product. The same four products were released during growth of the organisms in complex medium, but the relative proportions differed suggesting that other substrates were being used. Both organisms contained enzymes of the glycolytic and pentose phosphate pathways, but while all activities of the TCA cycle were present in H. m. muscarum, NAD-linked isocitrate dehydrogenase, alpha-ketoglutarate dehydrogenase, succinate CoA synthase and succinate dehydrogenase were not detected in H. m. ingenoplastis. Fumarate reductase activity was present in both organisms. The data presented suggest that CO2-fixation and reverse flux through the TCA cycle may be important factors that enable the organisms to undergo anaerobiosis.