Mechanisms of Sugar Transport in the Rumen Bacterium Selenomonas ruminantium

Abstract

Toluene-treated cells of Selenomonas ruminantium HD4 used phosphoenolpyruvate (PEP) to phosphorylate glucose and sucrose. Glucose activity was constitutive, while the phosphorylation of sucrose was inducible. Competition experiments indicated that separate phosphotransferase (PTS) enzymes II were present for glucose and sucrose, but it appeared that maltose was hydrolysed by an inducible extracellular maltase and then transported by the glucose PTS. S. ruminantium HD4 grew more slowly on maltose than glucose or sucrose and the specific activity of maltase was rate limiting. The maltase was competitively inhibited by glucose and sucrose. Xylose was not phosphorylated by PEP or ATP, and its uptake was inhibited by the protonophore carbonyl cyanide m-chlorophenylhydrazone (CCCP), and by chlorhexidine diacetate. The absence of PEP-dependent phosphorylation and the effects of CCCP suggested that xylose was transported by an active transport mechanism.