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.
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
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.
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