Metabolic adaptation of Trichomonas vaginalis to growth rate and glucose availability.

The parasitic protist Trichomonas vaginalis adapted the specific activities of twelve of the enzymes involved in glucose metabolism to the growth rate an glucose availability. These changes in enzyme activities were induced by culturing T. vaginalis in chemostats with glucose, present in rate-limiting or excess concentrations, as carbon and energy source. The specific activities were measured in pelleted cells at each steady state, while metabolic end products were determined in filtered culture fluid. The specific activities were lower in cells grown on growth-rate-limiting concentrations of glucose and higher in organisms cultured in the presence of excess glucose. In both cases enzyme activities were higher at increasing growth rates. For most enzymes the difference between the highest and lowest activities was an order of magnitude. The specific activities of eleven of the enzymes were strongly correlated to each other (correlation coefficients 0.83-0.99), the exception being lactate dehydrogenase. The rates of production of the three major end products, lactate, acetate and glycerol, increased with increasing growth rates. Alanine was not formed in measurable quantities. The ratio of the end products formed was strongly influenced by the growth rates and glucose availability. The rates of formation of acetate and glycerol correlated best with the specific activities of the enzymes catalysing the final reactions of their respective pathways. This suggests that the production of acetate and glycerol is rate-limited by these final steps. In contrast, the formation of lactate did not correlate with the specific activity of lactate dehydrogenase but was determined by the rate of glucose consumption.