Cellobiose transport by mixed ruminal bacteria from a cow

The transport of cellobiose in mixed ruminal bacteria harvested from a hols tein cow fed an Italian ryegrass hay was determined in the presence of noji rimycin-1-sulfate, which almost inhibited cellobiase activity. The kinetic parameters of cellobiose uptake were 14 mu M for the K-m and 10 nmol/min/mg of protein for the V-max. Extracellular and cell-associated cellobiases we re detected in the rumen, with both showing higher V-max values and lower a ffinities than those determined for cellobiose transport. The proportion of cellobiose that was directly transported before it was extracellularly deg raded into glucose increased as the cellobiose concentration decreased, rea ching more than 20% at the actually observed levels of cellobiose in the ru men, which were less than 0.02 mM. The inhibitor experiment showed that cel lobiose was incorporated into the cells mainly by the phosphoenolpyruvate p hosphotransferase system and partially by an ATP-dependent and proton-motiv e-force-independent active transport system. This finding was also supporte d by determinations of phosphoenolpyruvate phosphotransferase-dependent NAD H oxidation,vith cellobiose and the effects of artificial potentials on cel lobiose transport. Cellobiose uptake was sensitive to a decrease in pH (esp ecially below 6.0), and it was weakly but significantly inhibited in the pr esence of glucose.