Sugar metabolism by fusobacteria: regulation of transport, phosphorylation, and polymer formation by Fusobacterium mortiferum ATCC 25557

Abstract

Strains of eight Fusobacterium species differed in the ability to use sugars as energy sources for growth. For Fusobacterium russii ATCC 25533, F. gonidiaformans ATCC 25563, and F. nucleatum ATCC 10953 (except for fructose), growth was marginal to poor on all of the sugars tested. Other species displayed reasonable growth on glucose, fructose, mannose, and galactose, and two strains of F. mortiferum (ATCC 25557 and ATCC 9817) grew well on six of the sugars tested, including sucrose and maltose. Glucose transport by resting cells of most of the species was dependent upon (or markedly stimulated by) the presence of a fermentable amino acid. By contrast, F. mortiferum cells rapidly accumulated glucose and other sugars in the absence of amino acids. Although these cells were constitutive for glucose uptake, accumulation of other sugars was specifically induced by growth of F. mortiferum on the appropriate sugar. Spectrophotometric analyses and in situ staining of anionic polyacrylamide gels showed that glucose and fructose (mannose) are phosphorylated by separate ATP-dependent kinases. Fructokinase was stable in air at 4 degrees C, but under these conditions, greater than 70% of the glucokinase activity was lost. After overnight dialysis of the extract, no glucokinase activity was detectable; however, 65% of the initial enzyme activity was retained by inclusion of 1 mM dithiothreitol in the dialysis buffer. Thin-section electron microscopy showed that cells of F. mortiferum produced various amounts of intracellular glycogen during growth on the following sugars (in decreasing order of formation): galactose greater than sucrose greater than glucose greater than mannose greater than fructose. Mechanisms for sugar transport regulation, phosphorylation, and polymer synthesis by F. mortiferum cells are proposed.