The Disruption of a Gene Encoding a Putative Arylesterase Impairs Pyruvate Dehydrogenase Complex Activity and Nitrogen Fixation in Sinorhizobium meliloti

Abstract

Nitrogen-fixing Sinorhizobium meliloti cells depend upon dicarboxylic acids as carbon and energy sources. The metabolism of these intermediate compounds of the tri-chloroacetic acid cycle is dependent upon the availability of acetyl-coenzyme A (CoA). In bacteroids, the combined activities of malic enzymes and pyruvate dehydrogenase (PDH) have been proposed to be responsible for the anaplerotic synthesis of acetyl-CoA. We obtained a S. meliloti mutant strain, PD3, in which a Tn5 insertion led to a significant decrease in the overall PDH activity. The genetic characterization of this mutant revealed that the transposon is located at the 3′ end of a gene (ada) encoding a putative arylesterase. The mutant PD3 is deficient in nitrogen fixation, which strengthens the physiological importance of PDH activity in the symbiosis of S. meliloti with alfalfa plants.

Keywords

• bacteroid metabolism
• nodulation
• succinate