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The Rhodobacter capsulatus genome contains three genes (olsA [plsC138], plsC316, and plsC3498) that are annotated as lysophosphatidic acid (1-acyl-sn-glycerol-3-phosphate) acyltransferase (AGPAT). Of these genes, olsA was previously shown to be an O-acyltransferase in the second step of ornithine lipid biosynthesis, which is important for optimal steady-state levels of c-type cytochromes (S. Aygun-Sunar, S. Mandaci, H.-G. Koch, I. V. J. Murray, H. Goldfine, and F. Daldal. Mol. Microbiol. 61:418-435, 2006). The roles of the remaining plsC316 and plsC3498 genes remained unknown. In this work, these genes were cloned, and chromosomal insertion-deletion mutations inactivating them were obtained to define their function. Characterization of these mutants indicated that, unlike the Escherichia coli plsC, neither plsC316 nor plsC3498 was essential in R. capsulatus. In contrast, no plsC316 olsA double mutant could be isolated, indicating that an intact copy of either olsA or plsC316 was required for R. capsulatus growth under the conditions tested. Compared to OlsA null mutants, PlsC316 null mutants contained ornithine lipid and had no c-type cytochrome-related phenotype. However, they exhibited slight growth impairment and highly altered total fatty acid and phospholipid profiles. Heterologous expression in an E. coli plsC(Ts) mutant of either R. capsulatus plsC316 or olsA gene products supported growth at a nonpermissive temperature, exhibited AGPAT activity in vitro, and restored phosphatidic acid biosynthesis. The more vigorous AGPAT activity displayed by PlsC316 suggested that plsC316 encodes the main AGPAT required for glycerophospholipid synthesis in R. capsulatus, while olsA acts as an alternative AGPAT that is specific for ornithine lipid synthesis. This study therefore revealed for the first time that some OlsA enzymes, like the enzyme of R. capsulatus, are bifunctional and involved in both membrane ornithine lipid and glycerophospholipid biosynthesis.

The clostridial clone pHH37 was determined by complementation of the plsB defect in mutant strains of Escherichia coli to investigate whether the plasmid expressed a gene that encodes a G3P acyltransferase. The PlsD protein sequences were characterized by a high degree of homology to the PlsC 1-acyl-G3P acyltransferase. However, the plasmid pSJ342 did not complement the 1-acyl-G3P acyltransferase mutation in strain SM2-1.

The study indicate a postulated accessory role for phoshatidylinositol-specific phospholipase C (PI-PLC) with listeriolysin O (LLO) in lysing the primary phagosome of a macrophage. Potential cooperative interactions of Listeria monocytogenes PI-PLC and LLO, a pore-forming hemolysin in a liposome lysis assay was studied. The effect of PI-PLC was not dependent on lipid hydrolysis and both proteins released insulin from liposomes. Membrane fusion did not follow membrane permeabilization.

The taxonomic status of Clostridium innocuum was based on its novel polar lipid composition, as the lipid amphiphiles exhibited differences from those of Acholeplasma laidlawii. The polar lipids of C. innocuum consisted of glycosyldiradylglycerols, phospholipids and phosphoglycolipids. A PG acetyl of cardiolipin plasmalogen was one of the newly found lipids.

The phosphatidylinositol-specific phospholipase C from Listeria monocytogenes has lower activity on glycosyl phosphatidylinositol-anchored proteins than phospholipase C from Bacillus thuringiensis. The L. monocytogenes enzyme have no activity on phosphatidylinositol 4,5-biphosphate and phosphatidylinositol 4-phosphate and acts specifically on phosphatidylinositol.

Phospholipase C (PLC), an enzyme secreted by Listeria monocytogenes, is responsible for the hydrolylsis of phosphatidylethanolamine and phosphatidylglycerol that takes place after the dispersion of Escherichia coli phospholipids in Triton X-100. PCL promotes the hydrolysis of PE, the plasmalogen form of PE, the glycerol acetal of PE and cardiolipin. The hydrolytic activity of cardiolipin is stimulated by I-, Cl- and F- on Pc-Triton X-100 mixed micelles.

The effect of modifying the fatty acid substrates in a biotin free medium on the membrane lipid composition in Clostridium acetobutylicum was examined in order to develop strategies for enhanced solvent resistance. The results showed that C. acetobutylicum grown in the absence of biotin can alter its lipid composition to promote bilayer stability. These changes involve phospholipids, glycolipids of the diglyceride type and phosphoglycolipids of unknown structures. These lipids are regulated in order to provide a relatively constant phase state of the membrane lipids.

The kinetic activation and specific activities of the phosphatidylinositol-specific phospholipase C (PI-PLC) obtained from Listeria monocytogenes are discussed. PI-PLC is shown to exhibit an extremely high affinity for the anionic phospholipids and hence can be employed for L. monocytogenes infectivity.