Alternative pathways of glucose transport in Prevotella bryantii B(1)4

Prevotella bryantii B(1)4 grew faster on glucose than mannose (0.70 versus 0.45 h(-1)); but these sugars were used simultaneously rather than diauxica lly. 2-deoxy-glucose (2DG) decreased the growth rate of cells that were pro vided with either glucose or mannose, bur 2DG did not completely prevent gr owth. Cells grown on glucose or mannose transported both C-14-glucose and C -14-mannose, but cells grown on glucose had over three-fold higher rates of C-14-glucose transport than cells grown on mannose. The C-14-mannose trans port rates of glucose- and mannose-grown cells were similar. Woolf-Augustin sson-Hofstee plots were not linear, and it appeared that the glucose/mannos e/2DG carrier acted as a facilitated diffusion system at high substrate con centrations. When cultures were grown on nitrogen-deficient (excess sugar) medium, isolates had three-fold lower C-14-glucose transport, but the C-14- mannose transport did not change significantly. C-14-glucose and C-14-manno se transport rates could be inhibited by 2DG and either mannose or glucose, respectively. The C-14-glucose transport of mannose-grown cells was inhibi ted more strongly by mannose and 2DG than those grown on glucose. Cells gro wn on glucose or mannose had similar ATP-dependent glucokinase activity, an d 2DG was a competitive inhibitor (K-i=0.75 mM). Thin layer chromatography indicated that cell extracts also had ATP-dependent mannose phosphorylation , bur only a small amount of phosphorylated 2DG was detected. Glucose, mann ose or 2DG were not phosphorylated in the presence of PEP. Based on these r esults, it appeared that P. bryantii B(1)4 had: (1) two mechanisms of gluco se transport, a constitutive glucose/mannose/2DG carrier and an alternative glucose carrier that was regulated by glucose availability, (2) an ATP-dep endent glucokinase that was competitively inhibited by 2DG but was unable t o phosphorylate 2DG at a rapid rate, and (3) virtually no PEP-dependent glu cose, mannose or 2DG phosphorylation activities. (C) 2000 Federation of Eur opean Microbiological Societies. Published by Elsevier Science B.V. All rig hts reserved.