title: Contribution of chemical changes in membrane lipids to the osmoadaptation of the halophilic bacterium Chromohalobacter salexigens.
abstract: The long-term response of the broad-salt growing halophile Chromohalobacter salexigens DSM 3043T to salt stress has been investigated with respect to adaptive changes in membrane lipid composition. This study included the wild-type and three salt-sensitive, ectoine-deficient strains: CHR62 (ectA::Tn1732, unable to grow above 0.75 M NaCl), CHR63 (ectC::Tn1732, unable to grow above 1.5 M NaCl), and CHR64, which was able to grow in minimal medium M63 up to 2.5 M NaCl, but its growth was slower than the wild-type strain at salinities above 1.5 M NaCl. This mutant accumulated ectoine and hydroxyectoine as major compatible solutes, but also the ectoine precursor, N-gamma-acetyldiaminobutyric acid, and was found to be affected in the ectoine synthase gene ectC. The main phospholipids of the wild-type strain were phosphatidylethanolamine, phosphatidylglycerol (PG), and cardiolipin (CL). Major fatty acids were detected as 16:0, 18:1, and 16:1, including significant amounts of cyc-19:0, and cyc-17:0. CL and cyclopropane fatty acids (CFA) levels were elevated when the wild-type strain was grown at high salinity (2.5 M NaCl). Membranes of the most salt-sensitive trains CHR62 and CHR63, but not of the less salt-sensitive strain CHR64, contained lower levels of CL. The proportion of cyc-19:0 in CHR64 was three-fold (at 2.0M NaCl) and 2.5-fold (at 2.5 M NaCl) lower than that of the wild type, suggesting that this mutant has a limited capacity to incorporate CFA into phospholipids at high salt. The addition of 1 mM ectoine to cultures of the wild-type strain increased the ratio PG/CL from 1.8 to 3.3 at 0.75 M NaCl, and from 1 to 6.5 at 2.5 M NaCl, and led to a slight decrease in CFA content. Addition of 1 mM ectoine to the mutants restored the steady-state levels of CL and CFA found in the wild-type strain supplemented with ectoine. These findings suggest that exogenous ectoine might attenuate the osmostress response involving changes in membrane lipids.
authors.affiliation: Department of Microbiology and Parasitology, Faculty of Pharmacy, University of Seville, 41012 Seville, Spain.
authors.forename: Carmen
authors.initials: C
authors.lastname: Vargas
authors.forename: Aris
authors.initials: A
authors.lastname: Kallimanis
authors.forename: Anna I
authors.initials: AI
authors.lastname: Koukkou
authors.forename: María I
authors.initials: MI
authors.lastname: Calderon
authors.forename: David
authors.initials: D
authors.lastname: Canovas
authors.forename: Fernando
authors.initials: F
authors.lastname: Iglesias-Guerra
authors.forename: Constantin
authors.initials: C
authors.lastname: Drainas
authors.forename: Antonio
authors.initials: A
authors.lastname: Ventosa
authors.forename: Joaquín J
authors.initials: JJ
authors.lastname: Nieto
mesh_terms: D000222:Adaptation, Physiological; D000599:Amino Acids, Diamino / Q000096:biosynthesis / Q000494:pharmacology; D002462:Cell Membrane / Q000187:drug effects; D044129:Halomonadaceae / Q000235:genetics / Q000502:physiology*; D006836:Hydro-Lyases / Q000235:genetics; D008563:Membrane Lipids / Q000737:chemistry*; D009994:Osmolar Concentration; D010743:Phospholipids / Q000737:chemistry
chemical_list: D000599:Amino Acids, Diamino; D008563:Membrane Lipids; D010743:Phospholipids; C045628:ectoine; D006836:Hydro-Lyases; C106231:ectoine synthase