The transcriptional activator NtrC controls the expression and activity ofglutamine synthetase in Herbaspirillum seropedicae

The role of the Nif(-) system in Herbaspirillum seropedicae was determined via ntrB and ntrC mutants. Three phenotypes were identified in these mutant s: Nif(-) deficiency in growth using nitrate, and low glutamine synthetase (GS) activity. All phenotypes were restored by the plasmid pKRT1 containing the intact glnA, ntrB and ntrC genes of H. seropedicae. The promoter regio n of glnA was subcloned into a beta -galactosidase fusion vector and the re sults suggested that NtrC positively regulates the glnA promoter in respons e to low nitrogen. The H. seropedicae ntrC and ntrB mutant strains showed a deficiency of adenylylalion/deadenylylation of GS, indicating that NtrC an d NtrB are involved in both transcription and activity control of GS in thi s organism. (C) 2000 Federation of European Microbiological Societies. publ ished by Elsevier Science B.V. All rights reserved.