Thirteen mutants unable to grow on pyruvate have been isolated from the facultative methylotroph 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 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 C, C and C 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 C, C and C compounds in this organism.


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