A Survey of the physiological role of malic enzymes in tropical Rhizobia

Abstract

NAD-malic enzyme (DME) and NADP-malic enzyme (TME) have been believed to play a key role in energy metabolism for nitrogenase reaction in bacteroids. To elucidate the physiological role of the malic enzymes in Bradyrhizobium japonicum bacteroids, a putative malic enzyme gene Bjtme1 was cloned by PCR using draft sequence data of the Bradyrhizobium japonicum USDA110 genome sequence project. To confirm the characteristics of the Bjtme1 gene, the protein encoded by this gene was over-expressed using a pET32a(+). Using twenty-six isolates which were obtained from nodules of various legume plants in Thailand, the distribution of the activities of both DME and TME was surveyed. The malic enzyme activities were present in all the isolated rhizobia and in 17 other local Bradyrhizobium strains in Thailand. In almost all the rhizobia, the DME activity predominated whereas the TME activity predominated only in the Rhizobium gallicum strains that were major symbionts of Sesbania rostrata.