Differential effects of permeating and nonpermeating solutes on the fatty acid composition of Pseudomonas putida

We examined the effect of reduced water availability on the fatty acid comp osition of Pseudomonas putida strain mt-2 grown in a defined medium in whic h the water potential was lowered with the permeating solutes NaCl or polye thylene glycol (PEG) with a molecular weight of 200 (PEG 200) or the nonper meating solute PEG 8000, Transmission electron microscopy showed that -1.0- MPa PEG 8000-treated cells had convoluted outer membranes, whereas -1.0-MPa NaCl-treated or control cells did not. At the range of water potential (-0 .25 to -1.5 MPa) that we examined, reduced water availability imposed by PE G 8000, but not by NaCl or PEG 200, significantly altered the amounts of tr ans and cis isomers of monounsaturated fatty acids that were present in who le-cell fatty acid extracts. Cells grown in basal medium or under the -0.25 -MPa water potential imposed by NaCl or PEG 200 had a higher trans:cis rati o than -0.25-MPa PEG 8000-treated cells, As the water potential was lowered further with PEG 8000 amendments, there was an increase in the amount of t rans isomers, resulting in a higher trans:cis ratio. Similar results were o bserved in cells grown physically separated from PEG 8000, indicating that these changes were not due to PEG toxicity, When cells grown in -1.5-MPa PE G 8000 amendments were exposed to a rapid water potential increase of 1.5 M Pa or to a thermodynamically equivalent concentration of the permeating sol ute, NaCl, there was a decrease in the amount of trans fatty acids with a c orresponding increase in the cis isomer, The decrease in the trans/cis rati o following hypoosomotic shack did not occur in the presence of the lipid s ynthesis inhibitor cerulenin or the growth inhibitors chloramphenicol and r ifampicin, which indicates a constitutively operating enzyme system. These results indicate that thermodynamically equivalent concentrations of permea ting and nonpermeating solutes have unique effects on membrane fatty acid c omposition.