An NMR and enzyme study of the carbon metabolism of Neisseria meningitidis

The pathogenic neisseriae are fastidious bacteria that are only able to gro w on a restricted range of carbon sources. The genome sequence of Neisseria meningitidis strain MC58 predicts the presence of a complete citric acid c ycle (CAC), but there have been no detailed biochemical studies of carbon m etabolism in this important pathogen, In this study, both NMR and conventio nal enzyme assays were used to investigate the central metabolic pathways o f a serogroup B strain (K454), C-13-NMR labelling patterns of amino acids f rom hydrolysed cell proteins after growth with either 2- or 3-[C-13]pyruvat e were consistent with the operation of a complete oxidative CAC, Enzyme as says showed that cell-free extracts contained all the CAC enzymes predicted from the genome sequence, including a membrane-bound malate:quinone oxidor eductase which is present in place of the conventional NAD-linked cytoplasm ic malate dehydrogenase. H-1-NMR studies showed that growth on glucose, lac tate and, especially, pyruvate. resulted in the excretion of significant am ounts of acetate into the culture supernatant. This occurred via the phosph otransacetylase (PTA)-acetate kinase (ACK) pathway. Extremely high specific activities of PIA (7-14 mu mol min(-1) mg(-1)) were detected in cell-free extracts, although ACK activities were much lower (46-298 nmol min(-1) mg(- 1)), Expression of PTA and ACK activities was not co-ordinately regulated d uring growth on combinations of carbon sources. This may be related to the presence of two ackA paralogues in N, meningitidis which are, unusually, un linked to the pta gene.