Electron paramagnetic resonance studies of the membrane fluidity of the foodborne pathogenic psychrotroph Listeria monocytogenes

摘要

Listeria monocytogenes is a foodborne psychrotrophic pathogen that grows at refrigeration temperatures. Previous studies of fatty acid profiles of wild-type and cold-sensitive, branched-chain fatty acid deficient mutants of L. monocytogenes suggest that the fatty acid 12-methyltetradecanoic (anteiso-C_(15:0)) plays a critical role in low-temperature growth of L. monocytogenes, presumably by maintaining membrane fluidity. The fluidity of isolated cytophasmic membranes of wild-type (SLCC53 and 10403S), and a cold-sensitive mutant (cld-1) of L. monocytogenes, grown with and without the supplementation of 2-methylbutyric acid, has been studied using a panel of hydrocarbon-based nitroxides (2N10, 3N10, 4N10, and 5N10) and spectral deconvolution and simulation methods to obtain directly the Lorentzian line widths and hence rotational correlation times (τ_c) and motional anisotropies of the nitroxides in the fast motional region. τ_c values over the temperature range of -7 ℃ to 50 ℃ were similar for the membranes of strains SLCC53 and 10403S grown at 10 ℃ and 30 ℃, and for strain cld-l grown with 2-methylbutyric acid supplementation (which restores branched-chain fatty acids) at 30 ℃. However, strain cld-l exhibited a threefold higher τ_c when grown without 2-methylbutyric acid supplementation (deficient in branched-chain fatty acids) compared to strains SLCC53, 10403S, and supplemented cld-l. No evidence was seen for a clear lipid phase transition in any sample. We conclude that the fatty acid anteiso-C_(15:0) imparts an essential fluidity to the L. monocytogenes membrane that permits growth at refrigeration temperatures.