title: Interaction between Nitrogen and Phosphate Stress Responses inSinorhizobium meliloti.
abstract: Bacteria have developed various stress response pathways to improve their assimilation and allocation of limited nutrients, such as nitrogen and phosphate. While both the nitrogen stress response (NSR) and phosphate stress response (PSR) have been studied individually, there are few experiments reported that characterize effects of multiple stresses on one or more pathways inSinorhizobium meliloti, a facultatively symbiotic, nitrogen-fixing bacteria. The PIIproteins, GlnB and GlnK, regulate the NSR activity, but analysis of global transcription changes in a PIIdeficient mutant suggest that theS. melilotiPIIproteins may also regulate the PSR. PIIdouble deletion mutants grow very slowly and pseudoreversion of the slow growth phenotype is common. To understand this phenomenon better, transposon mutants were isolated that had a faster growing phenotype. One mutation was inphoB, the response regulator for a two component regulatory system that is important in the PSR.phoB::Tn5mutants had different phenotypes in the wild type compared to a PIIdeficient background. This led to the hypothesis that phosphate stress affects the NSR and conversely, that nitrogen stress affects the PSR. Our results show that phosphate availability affects glutamine synthetase activity and expression, which are often used as indicators of NSR activity, but that nitrogen availability did not affect alkaline phosphatase activity and expression, which are indicators of PSR activity. We conclude that the NSR is co-regulated by nitrogen and phosphate, whereas the PSR does not appear to be co-regulated by nitrogen in addition to its known phosphate regulation.
authors.affiliation: School of Molecular Biosciences, Washington State University, PullmanWA, USA; Institute of Biological Chemistry, Washington State University, PullmanWA, USA.
authors.forename: Kelly L
authors.initials: KL
authors.lastname: Hagberg
authors.affiliation: Institute of Biological Chemistry, Washington State University, Pullman WA, USA.
authors.forename: Svetlana N
authors.initials: SN
authors.lastname: Yurgel
authors.affiliation: Institute of Biological Chemistry, Washington State University, Pullman WA, USA.
authors.forename: Monika
authors.initials: M
authors.lastname: Mulder
authors.affiliation: School of Molecular Biosciences, Washington State University, PullmanWA, USA; Institute of Biological Chemistry, Washington State University, PullmanWA, USA.
authors.forename: Michael L
authors.initials: ML
authors.lastname: Kahn
keywords: PII nitrogen regulatory proteins; Phob; alkaline phosphatase; glutamine synthetase; nitrogen stress; phosphate stress