Carbon and energy balances of glucose fermentation with hydrogenproducing bacterium Citrobacter amalonaticus Y19.

For the newly isolated H2-producing chemoheterotrophic bacterium Citrobacter amalonaticus Y19, anaerobic glucose metabolism was studied in batch cultivation at varying initial glucose concentrations (3.5- 9.5 g/l). The carbon-mass and energy balances were determined and utilized to analyze the carbon metabolic-pathways network. The analyses revealed (a) variable production of major metabolites (H2, ethanol, acetate, lactate, CO2, and cell mass) depending on initial glucose levels; (b) influence of NADH regeneration on the production of acetate, lactate, and ethanol; and (c) influence of the molar production of ATP on the production of biomass. The results reported in this paper suggest how the carbon metabolic pathway(s) should be designed for optimal H2 production, especially at high glucose concentrations, such as by blocking the carbon flux via lactate dehydrogenase from the pyruvate node.