Summary: Pseudomonasam1 is a facultative methylotroph which grows on a wide range of carbon compounds. A mutant of Pseudomonasam1 (ict41) grew only on C1 compounds and is thus an artificial obligate methylotroph. Measurements of activities of the components of the 2-oxoglutarate dehydrogenase complex suggest that the E2 component (dihydrolipoamide transsuccinylase) is not functional. All other tricarboxylic acid cycle enzymes were present with activities comparable to those in wild-type Pseudomonasam1 and cytochrome levels were unchanged in the mutant. Suspensions of the mutant oxidized pyruvate, lactate, β-hydroxybutyrate, acetoacetate and 2-oxoglutarate at very low rates. By contrast, C1 compounds were oxidized at the same rate as in wild-type bacteria. Two revertants of ict41 which regained 2-oxoglutarate dehydrogenase activity also regained the ability to oxidize and grow on the same substrates as wild-type bacteria. It is concluded that lack of 2-oxoglutarate dehydrogenase may well be the basis of obligate methylotrophy in some bacteria.
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