Phosphate-free ornithine lipid contents in Desulfovibrio spp. respond to growth temperature

Abstract Eight sulfate-reducing Desulfovibrio strains isolated from intertidal sediments of the North Sea were investigated for their intact polar lipid (IPL) composition. They contained two types of IPLs, phospholipids and aminolipids. The dominating phospholipids were phosphatidylethanolamine (PE), phosphatidylglycerol (PG) and, in lower concentration, diphosphatidylglycerol (DPG). Aminolipids formed a significant IPL fraction in all strains and high resolution tandem mass spectrometry assigned them as phosphate-free ornithine lipids (OLs). In intertidal flat sediments microorganisms may face strong temperature change on varying timescales and it is crucial for the microbes to maintain constant membrane fluidity, e.g. by modification of their membrane lipid composition. We therefore investigated whether or not these strains employ the same strategies for adjusting their membrane composition to growth temperature and, in particular, how OLs are modified. In all strains the relative OL content was found to be higher at higher growth temperature, in most cases at the expense of PE content and less often PG content. The fatty acid (FA) side chains of the main PE and PG species were similar, i.e. both were dominated by C 17 or C 18 , whereas C 15 FAs were additionally found as major OL side chains. The temperature-related side chain variation was similar for all IPLs: unsaturated FA content was lower at higher temperature. The corresponding FA patterns after hydrolysis revealed elevated branched FA content and anteiso / iso ratio at higher growth temperature. As the temperature-related changes in the IPL side chains were similar for all strains, we conclude that side chain modification plays a major role in the maintenance of membrane fluidity at higher temperature and that alternative roles of OLs in the membrane adaptation of Desulfovibrio spp. other than melting point adjustment are possible.