Effect of polyaromatic hydrocarbons (PAHs) on the membrane lipids of bacterial cell

Effect of polycyclic aromatic hydrocarbons (PAHs), namely naphthalene, acenaphtylene, pyrene and fluoranthene, as potential stress factors, on the growth, lipid amount, and fatty acid composition of the main membrane lipids (glycolipids, phosphatidylcholine and phosphatidylethanolamine) of Alcaligenes xylosoxidans was studied. Bacterial growth was significantly reduced by tested PAHs that were used from the start of cultivation. On the contrary, when PAHs were employed to the medium after 3 days of cultivation, growth of A. xylosoxidans was not affected but lipid accumulation in the. cell was usually improved in the range of 1.1-1.9 times. Palmitate and 9,10-methylene-hexadecanoate (C 17 cyclopropyl fatty acid; C 17-CP) comprised in general more than 90% from total fatty acids. While maximal levels of both C 17-CP, unsaturated C 18 fatty acids and C 20:1 were found in glycolipids, phosphatidylcholine contained only traces of unsaturated fatty acids. Index of fatty acid unsaturation in lipid structures was always lower in the presence of PAHs used after 3 days of cultivation in comparison with that observed when PAHs were employed at the beginning of cultivation. From all PAHs, only acenaphtylene enhanced biosynthesis of oleic, linoleic, and linolenic acids, which resulted in elevated index of fatty acid unsaturation.