INFLUENCE OF METRONIDAZOLE, CO, CO2, AND METHANOGENS ON THE FERMENTATIVE METABOLISM OF THE ANAEROBIC FUNGUS NEOCALLIMASTIX SP STRAIN L2

The effects of metronidazole, CO, methanogens, and CO, on the fermenta tion of glucose by the anaerobic fungus Neocallimastix sp. strain L2 w ere investigated. Both metronidazole and CO caused a shift in the ferm entation products from predominantly H-2, acetate, and formate to lact ate as the major product and caused a lower glucose consumption rate a nd cell protein yield. An increased lactate dehydrogenase activity and a decreased hydrogenase activity were observed in cells grown under b oth culture conditions. In metronidazole-grown cells, the amount of hy drogenase protein was decreased compared with the amount in cells grow n in the absence of metronidazole. When Neocallimastix sp. strain L2 w as cocultured with the methanogenic bacterium Methanobrevibacter smith ii, the fermentation pattern changed in the opposite direction: H-2 an d acetate production increased at the expense of the electron sink pro ducts lactate, succinate, and ethanol. A concomitant decrease in the e nzyme activities leading to these electron sink products was observed, as well as an increase in the glucose consumption rate and cell prote in yield, compared with those of pure cultures of the fungus. Low leve ls of CO2 in the gas phase resulted in increased H-2 and lactate forma tion and decreased production of formate, acetate, succinate, and etha nol, a decreased glucose consumption rate and cell protein yield, and a decrease in most of the hydrogenosomal enzyme activities. None of th e tested culture conditions resulted in changed quantities of hydrogen osomal proteins. The results indicate that manipulation of the pattern of fermentation in Neocallimastix sp. strain L2 results in changes in enzyme activities but not in the proliferation or disappearance of hy drogenosomes.