A GTP-driven central carbon metabolism in the cellulolytic bacterium Ruminiclostridium cellulolyticum

In Ruminiclostridium cellulolyticum, the hexokinase and galactokinase were formerly shown to strongly prefer GTP over ATP, whereas the phosphofructokinase is PPi-dependent, suggesting an unconventional central carbon metabolism in this anaerobic bacterium. Herein, the characterization of all other kinases of this pivotal pathway led to the identification of their preferred NTP/NDP. The kinases involved in the first reactions, primarily functioning as NTP-consuming enzymes, appear to be GTP-dependent. In contrast, the enzymes catalyzing the downstream steps that mainly generate NTP, show no marked preference. Consequently, its central carbon metabolism appears essentially driven by GTP, whose cellular content nears that of ATP. Interestingly, in vivo reciprocal exchange of the GTP-dependent hexokinase in R. cellulolyticum by the ATP-dependent glucokinase from Escherichia coli and vice versa generates modified strains that still catabolize glucose and glucose disaccharides. Altogether our data suggest an unexpected diversity and flexibility in the functioning of this central pathway in bacteria.