Stable-isotope studies of glutamate catabolism in Fusobacterium nucleatum

Catabolism of glutamate was investigated in Fusobacterium nucleatum, an anaerobic micro-organism that is strongly implicated in periodontal disease. The distribution of labels in acetate and butyrate derived from [13C]glutamates was determined by NMR spectroscopy and MS. The label from L-[5-13C]glutamate was not incorporated, whereas C-1 of acetate and butyrate were efficiently labelled by L-[1-13C]glutamate; these results indicated that the hydroxyglutarate pathway predominated. In butyrate, enrichment at C-3 was smaller than C-1; that this was not due to participation of the methylaspartate pathway was demonstrated by the incorporation of label from L-[4-13C]glutamate into only C-2 of acetate and C-4 (major)/C-2 (minor) of butyrate. The presence of label at a second site in butyrate was attributed to the synthesis of butyrate from acetate and verified by the incorporation of label from [1,2-13C2]- and [2H3]-acetate.