Excretion of metabolites by hydrogen bacteria

Summary

The respiration rate-dependent formation of metabolites and of poly-3-hydroxybutanoate was studied with wild type and mutant strains of Alcaligenes eutrophus. Several metabolites were excreted during restricted respiration, each metabolite at a distinct relative respiration rate. The relative respiration rate was defined as the ratio (in percent) of the respiration rate during the production phase to that at the end of the exponential growth phase. The following metabolites were excreted: Ethanol, 1-propanol and 2-methyl-1-propanol at 2.4, D,L-2,3-butanediol at 4.4, meso-2,3-butanediol at 5.1, acetoin at 4.4 to 5.5, 2-methylpropanoate, 2-methylbutanoate and 3-methylbutanoate at 5 to 6, succinate at 5.5, formate at 6.7, molecular hydrogen at 5 to 7, acetate at 7.2, butanoate at 7.4, 3-hydroxybutanoate at 10 to 11, cis-aconitate at 20.6, 2-oxo-3-methylbutanoate at 26.5, and 2-oxoglutarate at about 50%. The maximum formation of poly-3-hydroxybutanoate occurred at 40 to 50%. When the respiration rate was not restricted, the substrate was completely oxidized. The excretion of metabolites is a very useful indicator for the oxygen nutrition of the cells.

The respiration rate correlated positively with the availability of oxygen and negatively with that of gluconate. Upon addition of gluconate (1.5%), the respiration rate immediately decreased.