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Journal of Bacteriology, July 2004, p. 4638-4644, Vol. 186, No. 14
0021-9193/04/$08.00+0     DOI: 10.1128/JB.186.14.4638-4644.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Differences in Membrane Fluidity and Fatty Acid Composition between Phenotypic Variants of Streptococcus pneumoniae

Barak Aricha,1 Itzhak Fishov,2 Zvi Cohen,3 Noga Sikron,1 Stella Pesakhov,1 Inna Khozin-Goldberg,3 Ron Dagan,1 and Nurith Porat1*

Pediatric Infectious Disease Unit, Soroka University Medical Center, Faculty of Health Sciences,1 Microalgal Biotechnology Laboratory, A. Katz Department of Dry Lands Biotechnologies, J. Blaustein Institute for Desert Research, Sde Boker Campus,3 Department of Life Sciences, Ben-Gurion University of the Negev, Beer Sheva, Israel2

Received 26 September 2003/ Accepted 25 March 2004

Phase variation in the colonial opacity of Streptococcus pneumoniae has been implicated as a factor in the pathogenesis of pneumococcal disease. This study examined the relationship between membrane characteristics and colony morphology in a few selected opaque-transparent couples of S. pneumoniae strains carrying different capsular types. Membrane fluidity was determined on the basis of intermolecular excimerization of pyrene and fluorescence polarization of 1,6-diphenyl 1,3,5-hexatriene (DPH). A significant decrease, 16 to 26% (P ≤ 0.05), in the excimerization rate constant of the opaque variants compared with that of the transparent variants was observed, indicating higher microviscosity of the membrane of bacterial cells in the opaque variants. Liposomes prepared from phospholipids of the opaque phenotype showed an even greater decrease, 27 to 38% (P ≤ 0.05), in the pyrene excimerization rate constant compared with that of liposomes prepared from phospholipids of bacteria with the transparent phenotype. These findings agree with the results obtained with DPH fluorescence anisotropy, which showed a 9 to 21% increase (P ≤ 0.001) in the opaque variants compared with the transparent variants. Membrane fatty acid composition, determined by gas chromatography, revealed that the two variants carry the same types of fatty acids but in different proportions. The trend of modification points to the presence of a lower degree of unsaturated fatty acids in the opaque variants compared with their transparent counterparts. The data presented here show a distinct correlation between phase variation and membrane fluidity in S. pneumoniae. The changes in membrane fluidity most probably stem from the observed differences in fatty acid composition.

* Corresponding author. Mailing address: Pediatric Infectious Disease Unit, Soroka University Medical Center, P.O. Box 151, Beer Sheva 84101, Israel. Phone: 972-8-6400839. Fax: 972-8-6232334. E-mail: npurat{at}bgumail.bgu.ac.il.

Journal of Bacteriology, July 2004, p. 4638-4644, Vol. 186, No. 14
0021-9193/04/$08.00+0     DOI: 10.1128/JB.186.14.4638-4644.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.



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