Biosynthesis of ω-alicyclic fatty acids induced by cyclic precursors and change of membrane fluidity in thermophilic bacteria Geobacillus stearothermophilus and Meiothermus ruber.

Two thermophilic strains belonging to Geobacillus stearothermophilus and Meiothermus ruber, which naturally do not synthesize ω-alicyclic fatty acids (ω-FAs) were cultivated with cyclopropyl, cyclobutyl, cyclopentyl and cyclohexyl carboxylic acids. Gas chromatography-mass spectrometry analysis of fatty acid methyl and picolinyl esters showed that both strains are able to synthesize ω-FAs when cultivated with the appropriate precursor. The incorporation of cyclic acids influenced the whole FA composition as well as membrane fluidity. Membrane fluidity of intact cells was studied by measuring the fluorescence polarisation of the probe l,6-diphenyl-1,3,5-hexatriene incorporated into membrane lipid bilayers. Cytoplasmic membrane became more fluid with increasing content of ω-FAs. This is caused by considerable changes in lipid packing within the membrane induced by the presence of ω-FAs not found in the natural environment of Geobacillus and Meiothermus strains.