Two Lipid Signals Guide Fruiting Body Development of Myxococcus xanthus

Abstract

Myxococcus xanthus produces several extracellular signals that guide fruiting body morphogenesis and spore differentiation. Mutants defective in producing a signal may be rescued by codevelopment with wild-type cells or cell fractions containing the signal. In this paper, we identify two molecules that rescue development of the E signal-deficient mutant LS1191 at physiological concentrations, iso15:0 branched-chain fatty acid (FA) and 1-iso15:0-alkyl-2,3-di-iso15:0-acyl glycerol (TG1), a development-specific monoalkyl-diacylglycerol. The physiological concentrations of the bioactive lipids were determined by mass spectrometry from developing wild-type cells using chemically synthesized standards. Synthetic TG1 restored fruiting body morphogenesis and sporulation and activated the expression of the developmentally regulated gene with locus tag MXAN_2146 at physiological concentrations, unlike its nearly identical tri-iso15:0 triacylglycerol (TAG) counterpart, which has an ester linkage instead of an ether linkage. iso15:0 FA restored development at physiological concentrations, unlike palmitic acid, a straight-chain fatty acid. The addition of either lipid stimulates cell shortening, with an 87% decline in membrane surface area, concomitantly with the production of lipid bodies at each cell pole and in the center of the cell. We suggest that cells produce triacylglycerol from membrane phospholipids. Bioactive lipids may be released by programmed cell death (PCD), which claims up to 80% of developing cells, since cells undergoing PCD produce lipid bodies before lysing.

Neutral and Phospholipids of the Myxococcus xanthus Lipodome during Fruiting Body Formation and Germination

“…Analysis of the lipid body composition indicated that ether lipids, especially TG1, are the most abundant lipid species, followed by TAGs (12). TG1 is produced only during the sporulation of M. xanthus (8), has been shown to have signaling functions, and promotes the expression of a developmentally regulated gene (10). Therefore, it is possible that ether lipids, incorporated into lipid bodies and also released into the fruiting body, are used as communication signals.…”

“…Lipids containing ether-linked fatty acids accumulate during development, with a maximum amount occurring at about 48 h after the onset of starvation (8,9). The most dominant ether lipid, 1-iso-15:0-alkyl-2,3-di-iso-15:0-acyl glycerol (TG1), has been reported to be a signal involved in myxobacterial development (10). Also, the plasmenylphosphatidylethanolamine vinyl ether lipid phosphatidylethanolamine(P-iso-15:0/iso-15:0) (VEPE) was previously described to be a biomarker for development (9).…”

An iso-15 : 0 O-alkylglycerol moiety is the key structure of the E-signal in Myxococcus xanthus

“…The complementation with lipids was performed according to Bhat et al (2014) with modifications. Bacteria were harvested at OD 600 1-1.2 and concentrated to a density of 5|10 9 cells ml…”

“…A knockout of elbD results in a mutant with delayed fruiting body formation and a defect in sporulation, indicating the importance of the ether lipids to complete development (Lorenzen et al, 2014). Both iso-15 : 0 FA and TG1 have already been referred to as signals, or at least precursors, for a molecule functioning in E-signalling (Bhat et al, 2014). However, it remains unclear which structural moieties of both molecules are actually forming the signalophore for aggregation, fruiting body formation and sporulation.…”

“…This defect can be complemented by isovalerate providing the starting unit for branched-chain FA biosynthesis or directly by adding iso-15 : 0 FA during development . Beyond that, the monoalkyl diacylglycerol TG1 (1-iso-15 : 0-alkyl-2,3-di-iso-15 : 0 acyl glycerol), which accumulates during development, is also capable of rescuing fruiting body formation and sporulation (Bhat et al, 2014). In M. xanthus, ether lipids are synthesized by the elb biosynthesis gene cluster, coding for the multidomain enzyme ElbD with similarity to polyketide synthases (Lorenzen et al, 2014).…”