CARBOHYDRATE UTILIZATION PATTERNS AND SUBSTRATE PREFERENCES IN BACTEROIDES-THETAIOTAOMICRON

Specific growth rates of Bacteroides thetaiotaomicron NCTC 10582 with either glucose, arabinose, mannose, galactose or xylose as sole carbon sources were 0.42/h, 0.10/h, 0.38/h, 0.38/h and 0.16/h respectively, suggesting that hexose metabolism was energetically more efficient tha n pentose fermentation in this bacterium. Batch culture experiments to determine whether carbohydrate utilization was controlled by substrat e-induced regulatory mechanisms demonstrated that mannose inhibited up take of glucose, galactose and arabinose, but had less effect on xylos e. Arabinose and xylose were preferentially utilized at high dilution rates (D>0.26/h) in carbon-limited continuous cultures grown on mixtur es of arabinose, xylose, galactose and glucose. When mannose was also present, xylose was co-assimilated at all dilution rates. Under nitrog en-limited conditions, however, mannose repressed uptake of all sugars , showing that its effect on xylose utilization was strongly concentra tion dependent. Studies with individual D-[U-C-14]-labelled substrates showed that transport systems for glucose, galactose, xylose and mann ose were inducible. Measurements to determine incorporation of these s ugars into trichloroacetic acid-precipitable material indicated that g lucose and mannose were the principal precursor monosaccharides. Xylos e was only incorporated into intracellular macro-molecules when it ser ved as growth substrate. Phosphoenolpyruvate:phosphotransferase system s were not detected in preliminary experiments to elucidate the mechan isms of sugar uptake, and studies with inhibitors of carbohydrate tran sport showed no consistent pattern of inhibition with glucose, galacto se, xylose and mannose. These results indicate the existence of a vari ety of different systems involved in sugar transport in B. thetaiotaom icron.