title: The lipid lysyl-phosphatidylglycerol is present in membranes of Rhizobium tropici CIAT899 and confers increased resistance to polymyxin B under acidic growth conditions.
abstract: Lysyl-phosphatidylglycerol (LPG) is a well-known membrane lipid in several gram-positive bacteria but is almost unheard of in gram-negative bacteria. In Staphylococcus aureus, the gene product of mprF is responsible for LPG formation. Low pH-inducible genes, termed IpiA, have been identified in the gram-negative alpha-proteobacteria Rhizobium tropici and Sinorhizobium medicae in screens for acid-sensitive mutants and they encode homologs of MprF. An analysis of the sequenced bacterial genomes reveals that genes coding for homologs of MprF from S. aureus are present in several classes of organisms throughout the bacterial kingdom. In this study, we show that the expression of lpiA from R. tropici in the heterologous hosts Escherichia coli and Sinorhizobium meliloti causes formation of LPG. A wild-type strain of R. tropici forms LPG (about 1% of the total lipids) when the cells are grown in minimal medium at pH 4.5 but not when grown in minimal medium at neutral pH or in complex tryptone yeast (TY) medium at either pH. LPG biosynthesis does not occur when lpiA is deleted and is restored upon complementation of lpiA-deficient mutants with a functional copy of the lpiA gene. When grown in the low-pH medium, lpiA-deficient rhizobial mutants are over four times more susceptible to the cationic peptide polymyxin B than the wild type.
authors.affiliation: Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Av. Universidad s/n, Apdo. Postal 565-A, Cuernavaca, Morelos, CP62210, Mexico. chsohlen@ccg.unam.mx
authors.forename: Christian
authors.initials: C
authors.lastname: Sohlenkamp
authors.forename: Kanaan A
authors.initials: KA
authors.lastname: Galindo-Lagunas
authors.forename: Ziqiang
authors.initials: Z
authors.lastname: Guan
authors.forename: Pablo
authors.initials: P
authors.lastname: Vinuesa
authors.forename: Sally
authors.initials: S
authors.lastname: Robinson
authors.forename: Jane
authors.initials: J
authors.lastname: Thomas-Oates
authors.forename: Christian R H
authors.initials: CR
authors.lastname: Raetz
authors.forename: Otto
authors.initials: O
authors.lastname: Geiger
mesh_terms: D001412:Bacillus subtilis / Q000235:genetics / Q000378:metabolism; D002462:Cell Membrane / Q000737:chemistry*; D003001:Cloning, Molecular; D024881:Drug Resistance, Bacterial; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D006863:Hydrogen-Ion Concentration; D008239:Lysine / Q000032:analysis*; D009876:Operon; D010715:Phosphatidylglycerols / Q000032:analysis*; D011112:Polymyxin B / Q000494:pharmacology*; D042162:Rhizobium tropici / Q000737:chemistry* / Q000187:drug effects*; D016962:Sinorhizobium meliloti / Q000235:genetics / Q000378:metabolism; D013211:Staphylococcus aureus / Q000235:genetics / Q000378:metabolism
chemical_list: D010715:Phosphatidylglycerols; C002285:lysylphosphatidylglycerol; D011112:Polymyxin B; D008239:Lysine