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Applied and Environmental Microbiology, June 2005, p. 3388, Vol. 71, No. 6
0099-2240/05/$08.00+0     doi:10.1128/AEM.71.6.3388.2005

LETTER TO THE EDITOR

Adaptation of Escherichia coli to Ethanol on the Level of Membrane Fatty Acid Composition


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LETTER
 
In a recent paper, Chiou et al. (1) described ethanol-mediated changes in the fatty acid composition of two different strains of Escherichia coli O157:H7.

Surprisingly, although the original literature was cited, the fatty acid composition of the bacteria shown in Table 2 of this paper is contradictory to many previous scientific publications on the fatty acid composition of E. coli. The fatty acid content of E. coli has been investigated intensively. This bacterium was shown to contain the saturated fatty acids 12:0, 14:0, 16:0, and 18:0; the unsaturated fatty acids 16:1{Delta}9cis and 18:1{Delta}11cis; and the cyclopropane fatty acids 17cyclo and 19cyclo (6, 8). Among these, the three fatty acids palmitic acid (16:0), palmitoleic acid (16:1{Delta}9cis), and cis-vaccenic acid (18:1{Delta}11cis) are the dominant ones that make up more than 90% of the fatty acid content in exponentially growing cells. Very recently, this fatty acid composition was also measured for E. coli strain O157:H7 (9, 10). Therefore, I have several concerns regarding the data and conclusions presented in the paper by Chiou et al. (1). (i) In E. coli, fatty acids are synthesized by the so-called anaerobic pathway of fatty acid biosynthesis (3, 8). There are no fatty acids present in this bacterium that are synthesized by the so-called aerobic pathway of fatty acid biosynthesis. Therefore, it is confusing that the authors report the presence of oleic acid (18:1{Delta}9cis). Instead, E. coli is expected to contain cis-vaccenic acid (18:1{Delta}11cis) as C18 unsaturated fatty acid (7). (ii) No odd-numbered fatty acids such as 17:0 or 19:0 have been detected in E. coli (3, 6). Therefore, it can be assumed that the peaks found in the chromatogram and presented in Table 2 (1) were the two cyclopropane fatty acids (17cyclo and 19cyclo) (4). (iii) No cis-trans isomerization of unsaturated fatty acids has been described in E. coli. This is substantiated by both genomic and physiological studies (2, 5, 7). Therefore, the reported presence of this isomerase in E. coli O157:H7 may be questioned.

In conclusion, errors caused by misidentification of fatty acid methyl ester chromatograms and maybe by the erroneous allocation of the single peaks to fatty acid standards may have contributed to the fatty acid composition reported in the paper of Chiou et al. (1).


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REFERENCES
 
    1
  1. Chiou, R. Y.-Y., R. D. Phillips, P. Zhao, M. P. Doyle, and L. R. Beuchat. 2004. Ethanol-mediated variations in cellular fatty acid composition and protein profiles of two genotypically different strains of Escherichia coli O157:H7. Appl. Environ. Microbiol. 70:2204-2210.[Abstract/Free Full Text]
    2. 2
  2. Cronan, J. E. 2002. Phospholipid modifications in bacteria. Curr. Opin. Microbiol. 5:202-205.[CrossRef][Medline]
    3. 3
  3. Cronan, J. E., Jr., and C. O. Rock. 1987. Biosynthesis of membrane lipids, p. 474-497. In F. C. Neidhardt, J. L. Ingraham, K. B. Low, B. Magasanik, M. Schaechter, and H. E. Umbarger (ed.), Escherichia coli and Salmonella typhimurium: cellular and molecular biology, vol. 1. American Society for Microbiology, Washington, D.C.
    4. 4
  4. Grogan, D. W., and J. E. Cronan. 1997. Cyclopropane ring formation in membrane lipids of bacteria. Microbiol. Mol. Biol. Rev. 61:429-441.[Abstract]
    5. 5
  5. Heipieper, H. J., F. Meinhardt, and A. Segura. 2003. The cis-trans isomerase of unsaturated fatty acids in Pseudomonas and Vibrio: biochemistry, molecular biology and physiological function of a unique stress adaptive mechanism. FEMS Microbiol. Lett. 229:1-7.[CrossRef][Medline]
    6. 6
  6. Ingram, L. O. 1976. Adaptation of membrane lipids to alcohols. J. Bacteriol. 125:670-678.[Abstract/Free Full Text]
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  7. Keweloh, H., and H. J. Heipieper. 1996. Trans unsaturated fatty acids in bacteria. Lipids 31:129-137.[Medline]
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  8. Magnuson, K., S. Jackowski, C. O. Rock, and J. E. Cronan, Jr. 1993. Regulation of fatty acid biosynthesis in Escherichia coli. Microbiol. Rev. 57:522-542.[Abstract/Free Full Text]
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  9. Yuk, H.-G., and D. L. Marshall. 2004. Adaptation of Escherichia coli O157:H7 to pH alters membrane lipid composition, verotoxin secretion, and resistance to simulated gastric fluid acid. Appl. Environ. Microbiol. 70:3500-3505.[Abstract/Free Full Text]
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  10. Yuk, H.-G., and D. L. Marshall. 2003. Heat adaptation alters Escherichia coli O157:H7 membrane lipid composition and verotoxin production. Appl. Environ. Microbiol. 69:5115-5119.[Abstract/Free Full Text]
Hermann J. Heipieper
Department of Bioremediation
UFZ Center for Environmental Research
Permoserstr. 15, 04318 Leipzig, Germany
Phone: 49 341 235 2772
Fax: 49 341 235 2492
E-mail: hermann.heipieper@ufz.de


Authors' Reply


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LETTER 
 
We appreciate the comments concerning the identification and nomenclature of fatty acids in E. coli O157:H7 (R. Y.-Y. Chiou, R. D. Phillips, P. Zhao, M. P. Doyle, and L. R. Beuchat, Appl. Environ. Microbiol. 70:2204-2210, 2004). The presence of cis-vaccenic acid (18:1{Delta}11cis) may have been detected but incorrectly reported as oleic acid (18:1{Delta}9cis), the trans-configured form being elaidic acid (18:1{Delta}9trans). The n-17:0 and n-19:0 fatty acids are incorrectly listed in Table 2. These acids should be listed as 17:0cyclo and 19:0cyclo, respectively. The possibility of isomerization mediated by ethanol stress of E. coli O157:H7 is being further investigated.

Robin Y.-Y. Chiou
Department of Food Science
National Chiayi University
Chiayi, Taiwan, Republic of China
Phone: 8865-2717613
Fax: 8865-2775524
E-mail: rychiou{at}mail.ncyu.edu.tw

Applied and Environmental Microbiology, June 2005, p. 3388, Vol. 71, No. 6
0099-2240/05/$08.00+0     doi:10.1128/AEM.71.6.3388.2005





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