Characterization of a glucose transport system in Vibrio parahaemolyticus

Cells of a glucose-PTS (phosphoenolpyruvate:carbohydrate phosphotransferase system)-negative mutant of Vibrio parahaemolyticus transport D-glucose in the presence of Na⁺. Maximum stimulation of D- glucose transport was observed at 40 mM NaCl, and Na⁺ could be replaced partially with Li⁺. Addition of D-glucose to the cell suspension under anaerobic conditions elicited Na⁺ uptake. Thus, we conclude that glucose is transported by a Na⁺/glucose symport mechanism. Calculated V(max) and K(m) values for the Na⁺-dependent D-glucose transport were 15 nmol/min/mg of protein and 0.57 mM, respectively, when NaCl was added at 40 mM. Na⁺ lowered the K(m) value without affecting the V(max) value. D-Glucose was the best substrate for this transport system, followed by galactose, α-D-fucose, and methyl-α-glucoside, judging from the inhibition pattern of the glucose transport. D-Glucose itself partly repressed the transport system when cells were grown in its presence.