The Metabolism of Pyruvate by the Facultative Methylotroph Pseudomonas AM1

Abstract

Thirteen mutants unable to grow on pyruvate have been isolated from the facultative methylotroph Pseudomonas AM1. Five of these lacked 2-oxoglutarate dehydrogenase and were thus obligate methylotrophs; one lacked the E1 (decarboxylase) component and the others probably lacked the E2 (transsuccinylase) component, but this could not be confirmed because transacylases could not be measured in the oxo-acid dehydrogenases of Pseudomonas AM1. Six mutants lacked pyruvate dehydrogenase (probably the E2, trans-acetylase, component) and one lacked both oxo-acid dehydrogenases. Although unable to oxidize pyruvate, one of the pyruvate dehydrogenase mutants was able to catalyse a coenzyme A-independent decarboxylation of pyruvate. The growth properties of the pyruvate dehydrogenase mutants confirmed that the loss of this enzyme is sufficient to confer on a previously facultative methylotroph the properties of a restricted facultative methyltroph similar to the hyphomicrobia. One mutant was only able to grow on C1, C2 and C3 compounds when a supplement of glyoxylate was added but was able to grow on other multicarbon compounds such as succinate. This confirms that there is a common reaction in the pathways for assimilation of C1, C2 and C3 compounds in this organism.