Factors affecting glucose and maltose phosphorylation by the ruminal bacterium Megasphaera elsdenii

The objectives of this study were to examine the effects of growth substrat e and extracellular pH on phosphoenolpyruvate-dependent glucose phosphoryla tion as well as to examine how maltose is phosphorylated by the ruminal bac terium Megasphaera elsdenii B159. Phosphoenolpyruvate-dependent glucose pho sphorylation by toluene-treated cells was constitutive, and glucose phospho rylation was reduced by 69% at pH 5.0, When toluene-treated cells were incu bated in histidine buffer, little maltose phosphorylation occurred in the a bsence of inorganic phosphate, However, the addition of increasing concentr ations of either potassium or sodium phosphate increased maltose phosphoryl ation. Maximal phosphorylation activity was observed at between 25 and 50 n lM of either inorganic phosphate source. Compared with the control incubati ons, maltose phosphorylation was increased over threefold with 25 mM of eit her potassium or sodium phosphate. Phosphoglucomutase activity was detected in cell extracts of M. elsdenii B159, and this enzyme had a K-m of 3.2 mM for glucose-1-P and a V-max of 1836 nmol of NADP(+) reduced/mg of protein p er min, Maltose was also hydrolyzed by an inducible maltase (K-m, 1.19 mM), To our knowledge, this is the first report of a maltose phosphorylase and a maltase in M. elsdenii.