title: The Sinorhizobium medicae WSM419 lpiA gene is transcriptionally activated by FsrR and required to enhance survival in lethal acid conditions.
abstract: Sinorhizobium medicae WR101 was identified as a mutant of WSM419 that contained a minitransposon-induced transcriptional gusA fusion activated at least 20-fold at pH 5.7. The expression of this fusion in moderately acid conditions was dependent on the calcium concentration; increasing the calcium concentration to enhance cell growth and survival in acid conditions decreased the expression of the fusion. A gene region containing the gusA fusion was sequenced, revealing five S. medicae genes: tcsA, tcrA, fsrR, lpiA and acvB. The gusA reporter in WR101 was fused to lpiA, which encodes a putative transmembrane protein also found in other Alphaproteobacteria such as Sinorhizobium meliloti, Rhizobium tropici and Agrobacterium tumefaciens. As LpiA has partial sequence similarity to the lysyl-phosphatidylglycerol (LPG) synthetase FmtC/MprF from Staphylococcus aureus, membrane lipid compositions of S. medicae strains were analysed. Cells cultured under neutral or acidic growth conditions did not induce any detectable LPG and therefore this lipid cannot be a major constituent of S. medicae membranes. Expression studies in S. medicae localized the acid-activated lpiA promoter within a 372 bp region upstream of the start codon. The acid-activated transcription of lpiA required the fused sensor-regulator product of the fsrR gene, because expression of lpiA was severely reduced in an S. medicae fsrR mutant. S. meliloti strain 1021 does not contain fsrR and acid-activated expression of the lpiA-gusA fusion did not occur in this species. Although acid-activated lpiA transcription was not required for cell growth, its expression was crucial in enhancing the viability of cells subsequently exposed to lethal acid (pH 4.5) conditions.
authors.affiliation: Centre for Rhizobium Studies, School of Biological Sciences and Biotechnology, Murdoch University, Murdoch, 6150, Western Australia.
authors.forename: Wayne G
authors.initials: WG
authors.lastname: Reeve
authors.affiliation: Centre for Rhizobium Studies, School of Biological Sciences and Biotechnology, Murdoch University, Murdoch, 6150, Western Australia.
authors.forename: Lambert
authors.initials: L
authors.lastname: Bräu
authors.affiliation: Department of Biochemistry and Molecular Biology, School of Biomedical and Chemical Sciences, University of Western Australia, Crawley, 6009, Western Australia.
authors.forename: Joanne
authors.initials: J
authors.lastname: Castelli
authors.affiliation: Dipartimento di Scienze Ambientali Agrarie e Biotecnologie Agro-Alimentari (Di.S.A.A.B.A.), University of Sassari, 07100 Sassari, Italy.
authors.forename: Giovanni
authors.initials: G
authors.lastname: Garau
authors.affiliation: Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, CP62210, Mexico.
authors.forename: Christian
authors.initials: C
authors.lastname: Sohlenkamp
authors.affiliation: Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, CP62210, Mexico.
authors.forename: Otto
authors.initials: O
authors.lastname: Geiger
authors.affiliation: Centre for Rhizobium Studies, School of Biological Sciences and Biotechnology, Murdoch University, Murdoch, 6150, Western Australia.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Dilworth
authors.affiliation: Office of the Pro Vice Chancellor (Research), University of Tasmania, Hobart, Tasmania, 7001, Australia.
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Glenn
authors.affiliation: Centre for Rhizobium Studies, School of Biological Sciences and Biotechnology, Murdoch University, Murdoch, 6150, Western Australia.
authors.forename: John G
authors.initials: JG
authors.lastname: Howieson
authors.affiliation: Centre for Rhizobium Studies, School of Biological Sciences and Biotechnology, Murdoch University, Murdoch, 6150, Western Australia.
authors.forename: Ravi P
authors.initials: RP
authors.lastname: Tiwari
mesh_terms: D000222:Adaptation, Physiological / Q000235:genetics; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001426:Bacterial Proteins / Q000096:biosynthesis* / Q000235:genetics*; D001483:Base Sequence; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D017353:Gene Deletion; D015964:Gene Expression Regulation, Bacterial; D005966:Glucuronidase / Q000032:analysis / Q000235:genetics; D006863:Hydrogen-Ion Concentration; D029902:Medicago / Q000382:microbiology; D008563:Membrane Lipids / Q000032:analysis; D050296:Microbial Viability; D008969:Molecular Sequence Data; D009586:Nitrogen Fixation; D011401:Promoter Regions, Genetic; D053204:Root Nodules, Plant / Q000382:microbiology; D017422:Sequence Analysis, DNA; D020579:Sinorhizobium / Q000235:genetics* / Q000502:physiology*; D015534:Trans-Activators / Q000502:physiology*
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D004269:DNA, Bacterial; C079999:LipA protein, Bacteria; D008563:Membrane Lipids; D015534:Trans-Activators; D005966:Glucuronidase