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Applied and Environmental Microbiology, June 2000, p. 2414-2421, Vol. 66, No. 6
0099-2240/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

Differential Effects of Permeating and Nonpermeating Solutes on the Fatty Acid Composition of Pseudomonas putidadagger

Larry J. Halverson1,* and Mary K. Firestone2

Departments of Agronomy and Microbiology, Iowa State University, Ames, Iowa 50011-1010,1 and Department of Environmental Science, Policy, and Management, University of California, Berkeley, California 94720-31102

Received 1 November 1999/Accepted 24 January 2000

We examined the effect of reduced water availability on the fatty acid composition of Pseudomonas putida strain mt-2 grown in a defined medium in which the water potential was lowered with the permeating solutes NaCl or polyethylene glycol (PEG) with a molecular weight of 200 (PEG 200) or the nonpermeating 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 PEG 8000, but not by NaCl or PEG 200, significantly altered the amounts of trans and cis isomers of monounsaturated fatty acids that were present in whole-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 ratio 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 trans isomers, resulting in a higher trans:cis ratio. Similar results were observed 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 PEG 8000 amendments were exposed to a rapid water potential increase of 1.5 MPa or to a thermodynamically equivalent concentration of the permeating solute, NaCl, there was a decrease in the amount of trans fatty acids with a corresponding increase in the cis isomer. The decrease in the trans/cis ratio following hypoosomotic shock did not occur in the presence of the lipid synthesis inhibitor cerulenin or the growth inhibitors chloramphenicol and rifampicin, which indicates a constitutively operating enzyme system. These results indicate that thermodynamically equivalent concentrations of permeating and nonpermeating solutes have unique effects on membrane fatty acid composition.

* Corresponding author. Mailing address: 2537 Agronomy Hall, Iowa State University, Ames, IA 50011-1010. Phone: (515) 294-0495. Fax: (515) 294-3163. E-mail: larryh{at}iastate.edu.

dagger Journal paper no. J-18636 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa, project no. IOW03439.

Applied and Environmental Microbiology, June 2000, p. 2414-2421, Vol. 66, No. 6
0099-2240/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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