The parasitic protist was cultured in chemostats with glucose or maltose as carbon and energy source. The maximum growth rate was about six divisions per day independent of the substrate, and the apparent for glucose was 0.375 mM. While growing on maltose, the growth rate depended linearly on the maltose concentration, indicating that in contrast to glucose metabolism a diffusion step is rate-limiting to maltose metabolism. Cultures were examined over a wide range of growth rates under four conditions: utilizing glucose or maltose as carbon and energy source, with the carbon source rate-limiting or present in excess. Cell density, cellular protein and carbohydrate content as well as residual substrate concentration in the culture fluid were measured at each steady state. The protein content was constant at 100 pg protein per cell except when was cultured under glucose limitation; in the latter case, slow-growing cells had less protein than cells grown at high rates. When growing under glucose limitation metabolism changed to become more energy efficient at growth rates exceeding about half the maximum rate. The maintenance energy at the low growth rates accounted for approximately half of the total carbon consumption, which is high in comparison to other micro-organisms. At low growth rates the yield on maltose exceeded that on glucose, when expressed in terms of carbon equivalents. The yields on maltose and glucose were equal, but much lower, when the carbon source was not rate-limiting. A comparison of the data of this study with similar studies on other organisms suggests that the high maintenance energy of may be used primarily for maintaining homeostasis of the internal conditions to enable growth and survival in the vagina.


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