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J Bacteriol, April 1998, p. 2194-2200, Vol. 180, No. 8
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

A Bacillus subtilis Gene Induced by Cold Shock Encodes a Membrane Phospholipid Desaturase

Pablo S. Aguilar,1 John E. Cronan Jr.,2,3 and Diego de Mendoza1,*

Programa Multidisciplinario de Biología Experimental and Departamento de Microbiología, Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, 2000-Rosario, Argentina,1 and Departments of Microbiology2 and Biochemistry,3 University of Illinois at Urbana-Champaign, Urbana, Illinois 61801

Received 2 January 1998/Accepted 20 February 1998

Bacillus subtilis grown at 37°C synthesizes saturated fatty acids with only traces of unsaturated fatty acids (UFAs). However, when cultures growing at 37°C are transferred to 20°C, UFA synthesis is induced. We report the identification and characterization of the gene encoding the fatty acid desaturase of B. subtilis. This gene, called des, was isolated by complementation of Escherichia coli strains with mutations in either of two different genes of UFA synthesis. The des gene encodes a polypeptide of 352 amino acid residues containing the three conserved histidine cluster motifs and two putative membrane-spanning domains characteristic of the membrane-bound desaturases of plants and cyanobacteria. Expression of the des gene in E. coli resulted in desaturation of palmitic acid moieties of the membrane phospholipids to give the novel mono-UFA cis-5-hexadecenoic acid, indicating that the B. subtilis des gene product is a Delta 5 acyl-lipid desaturase. The des gene was disrupted, and the resulting null mutant strains were unable to synthesize UFAs upon a shift to low growth temperatures. The des null mutant strain grew as well as its congenic parent at 20 or 37°C but showed severely reduced survival during stationary phase. Analysis of operon fusions in which the des promoter directed the synthesis of a lacZ reporter gene showed that des expression is repressed at 37°C, but a shift of cultures from 37 to 20°C resulted in a 10- to 15-fold increase in transcription. This is the first report of a membrane phospholipid desaturase in a nonphotosynthetic organism and the first direct evidence for cold induction of a desaturase.

* Corresponding author. Mailing address: Departamento de Microbiología, Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, Suipacha 531, 2000-Rosario, Argentina. Phone: 54-41-350596. Fax: 54-41-390465. E-mail: ddemendo{at}unromb.edu.ar.




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