Accumulation of Novel Glycolipids and Ornithine Lipids in Mesorhizobium loti under Phosphate Deprivation

Abstract

Glycolipids are found mainly in photosynthetic organisms (plants, algae, and cyanobacteria), Gram-positive bacteria, and a few other bacterial phyla. They serve as membrane lipids and play a role under phosphate deprivation as surrogates for phospholipids. Mesorhizobium loti accumulates different di-and triglycosyl diacylglycerols, synthesized by the processive glycosyltransferase Pgt-Ml, and two so far unknown glycolipids, which were identified in this study by mass spectrometry (MS) and nuclear magnetic resonance (NMR) spectroscopy as O-methyl-digalactosyl diacylglycerol (Me-DGD) and glucuronosyl diacylglycerol (GlcAD). Me-DGD is a novel glycolipid, whose synthesis depends on Pgt-Ml activity and the involvement of an unknown methyltransferase, while GlcAD is formed by a novel glycosyltransferase encoded by the open reading frame (ORF) mlr2668, using UDP-glucuronic acid as a sugar donor. Deletion mutants lacking GlcAD are not impaired in growth. Our data suggest that the different glycolipids in Mesorhizobium can mutually replace each other. This may be an adaptation mechanism to enhance the competitiveness in natural environments. A further nonphospholipid in Mesorhizobium was identified as a hydroxylated form of an ornithine lipid with the additional hydroxy group linked to the amide-bound fatty acid, introduced by the hydroxylase OlsD. The presence of this lipid has not been reported for rhizobia yet. The hydroxy group is placed on the C-2 position of the acyl chain as determined by NMR spectroscopy. Furthermore, the isolated ornithine lipids contained up to 80 to 90% D-configured ornithine, a stereoform so far undescribed in bacteria.

Carbon Oxidation State in Microbial Polar Lipids Suggests Adaptation to Hot Spring Temperature and Redox Gradients

“…Schubotz et al (2013); c. Yoshinaga et al (2011);d. Karlsson et al (1998); e. Ferreira et al (1999); f. this work (see Supplementary Material for mass spectral interpretation); g. Diercks et al (2015); h. Schubotz et al (2015); i. Yang et al (2006); j.…”

“…Only the chemical structure of the first two carbons of each alkyl chain are shown; with "chain" representing the rest. In FA-OH-FAm-OH (11), backbone-alkyl chain esterification may occur on either the 2 ′ or 3 ′ hydroxyl group (Diercks et al, 2015).…”

The Glycine Lipids of Bacteroides thetaiotaomicron Are Important for Fitness during Growth In Vivo and In Vitro

“…During periods of phosphate starvation, some bacteria access cellular phosphate reserves by using acylated amino acids such as OL to replace the phospholipids normally found in bacterial membranes (37)(38)(39). On the other hand, OL production in Rhizobium tropici and Burkholderia cepacia has been shown to be important for the normal tolerance of the bacterial cell to acid and temperature stress (13,40,41).…”

Bacterial ornithine lipid, a surrogate membrane lipid under phosphate‐limiting conditions, plays important roles in bacterial persistence and interaction with host

“…However, phosphate limitation results in dramatic increases in membrane OL contents. Under such conditions, OL constitutes up to 40% of total membrane lipids in S. proteamaculans , (Vences‐Guzman et al ., ), and hydroxylated OL accounted for 12% of total lipid in Mesorhizobium loti (a nodule‐forming bacterium) (Diercks et al ., ). These results indicate that OL serves as a surrogate of phospholipids under phosphate‐limiting environmental conditions.…”