COMPOSITION AND BIOPHYSICAL PROPERTIES OF LIPIDS IN XENORHABDUS-NEMATOPHILUS AND PHOTORHABDUS-LUMINESCENS, SYMBIOTIC BACTERIA ASSOCIATED WITH ENTOMOPATHOGENIC NEMATODES

Primary and secondary forms of Photorhabdus luminescens Hm and Xenorha bdus nematophilus N2-4 were grown at 18 and 28 degrees C for 24 to 96 h, and we made determinations of the fatty-acid compositions of total lipids and of the fluidity measured by 5-doxyl-stearic acid embedded i n liposomes made from total lipids, The levels of the unsaturated fatt y acids 16:1 and 18:1 (those with chain lengths of 16 or 18 and one do uble bond) generally were higher in primary-phase variants of P. lumin escens grown at 18 degrees C than in those grown at 28 degrees C. Prol onged culture at 18 degrees C caused the level of 18:1 to fall and rea ch that observed at 28 degrees C, The ratio of saturated to unsaturate d fatty acids rose with prolonged culture times in variants of each sp ecies at both phases, When grown at 18 degrees C, the proportion of 16 :1 in X. nematophilus was lower than in P. luminescens; the patterns o f temperature-induced changes were similar in these species, X. nemato philus contained a greater percentage of short-chain fatty acids (i.e. , with chain lengths of <14.0) than P. luminescens. Lipid liposomes fr om primary and secondary cultures of both bacterial species grown at 1 8 degrees C were more ordered (i.e., less fluid) than those grown at 2 8 degrees C, This result suggests the surprising absence of homeovisco us adaptation of membranes to temperature, Also, liposomes from primar y cultures were more ordered than those from secondary cultures and me mbranes from primary cultures of P. luminescens were more ordered at b oth culture temperatures than membranes from X. nematophilus. The biol ogical significance of the effect of growth conditions on membrane bio physical properties in these bacteria is discussed.