A Biochemical Basis for Obligate Methylotrophy: Properties of a Mutant of Pseudomonas AM1 lacking 2-Oxoglutarate Dehydrogenase

Pseudomonas AMI is a facultative methylotroph which grows on a wide range of carbon compounds. A mutant of Pseudomonas AMI (ICT4I) 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 Pseudomonas AMI and cytochrome levels were unchanged in the mutant. Suspensions of the mutant oxidized pyruvate, lactate, beta-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 ICT4I which regained 2-oxyoglutarate 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.