Open AccessA Rhizobium meliloti mutant, lacking a functional γ‐aminobutyrate (GABA) bypass, is defective in glutamate catabolism and symbiotic nitrogen fixation
Author(s) -
Fitzmaurice Ann Marie,
O'Gara Fergal
Publication year - 1993
Publication title -
fems microbiology letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.899
H-Index - 151
eISSN - 1574-6968
pISSN - 0378-1097
DOI - 10.1111/j.1574-6968.1993.tb06167.x
Subject(s) - biology , catabolism , rhizobium , glutamate receptor , biochemistry , mutant , glutamate dehydrogenase , nitrogen fixation , metabolism , nad+ kinase , glutamate synthase , metabolic pathway , enzyme , bacteria , gene , genetics , receptor
A Rhizobium meliloti mutant, CMF1 2:38, was isolated which was specifically defective in the degradation of glutamate as sole carbon and nitrogen source. Biochemical analysis of CMF1 2:38 revealed a reduction in succinic semialdehyde dehydrogenase (SSDH) activity, the third enzyme of the γ‐aminobutyrate (GABA) bypass. Evidence is presented which suggests that the Tn 5‐induced mutation in CMF1 2:38 exists in a regulatory gene governing the expression of both NAD and NADP‐linked SSDH activity. CMF1 2:38 nodulated alfalfa plants, but was reduced in its nitrogen fixation activity and biomass accumulating ability relative to the wild‐type strain. The results presented in this study indicate that the GABA bypass is a major mechanism of glutamate degradation in R. meliloti CMF1 and that glutamate catabolism via this pathway may play an important role in the symbiotic nitrogen fixation process.