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

Listeria monocytogenes is a foodborne psychrotrophic pathogen that grows at refrigeration temperatures. Previous studies of fatty acid profiles of wil d-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. monocytogene s, presumably by maintaining membrane fluidity. The fluidity of isolated cy toplasmic membranes of wild-type (SLCC53 and 10403S), and a cold-sensitive mutant (cld-1) of L. monocytogenes, grown with and without the supplementat ion of 2-methylbutyric acid, has been studied using a panel of hydrocarbon- based nitroxides (2N10, 3N10, 4N10, and 5N10) and spectral deconvolution an d simulation methods to obtain directly the Lorentzian line widths and henc e rotational correlation times (tau(c)) and motional anisotropies of the ni troxides in the fast motional region. tau(c) values over the temperature ra nge of -7 degrees C to 50 degrees C were similar for the membranes of strai ns SLCC53 and 10403S grown at 10 degrees C and 30 degrees C, and for strain cld-1 grown with 2-methylbutyric acid supplementation (which restores bran ched-chain fatty acids) at 30 degrees C. However, strain cld-1 exhibited a threefold higher tau(c) when grown without 2-methylbutyric acid supplementa tion (deficient in branched-chain fatty acids) compared to strains SLCC53, 10403S, and supplemented cld-1. No evidence was seen for a clear lipid phas e 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. (C) 2000 Elsevier Science B.V. All r ights reserved.