title: Differences in membrane fluidity and fatty acid composition between phenotypic variants of Streptococcus pneumoniae.
abstract: 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 < or = 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 < or = 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 < or = 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.
authors.affiliation: Pediatric Infectious Disease Unit, Soroka University Medical Center, P.O. Box 151, Beer Sheva 84101, Israel. npurat@bgumail.bgu.ac.il
authors.forename: Barak
authors.initials: B
authors.lastname: Aricha
authors.forename: Itzhak
authors.initials: I
authors.lastname: Fishov
authors.forename: Zvi
authors.initials: Z
authors.lastname: Cohen
authors.forename: Noga
authors.initials: N
authors.lastname: Sikron
authors.forename: Stella
authors.initials: S
authors.lastname: Pesakhov
authors.forename: Inna
authors.initials: I
authors.lastname: Khozin-Goldberg
authors.forename: Ron
authors.initials: R
authors.lastname: Dagan
authors.forename: Nurith
authors.initials: N
authors.lastname: Porat
mesh_terms: D002462:Cell Membrane / Q000737:chemistry*; D002849:Chromatography, Gas; D004161:Diphenylhexatriene / Q000737:chemistry / Q000378:metabolism; D005227:Fatty Acids / Q000032:analysis* / Q000502:physiology; D005231:Fatty Acids, Unsaturated / Q000032:analysis; D005454:Fluorescence Polarization; D014644:Genetic Variation; D008081:Liposomes / Q000737:chemistry; D008560:Membrane Fluidity; D008563:Membrane Lipids / Q000032:analysis; D010641:Phenotype; D010743:Phospholipids / Q000032:analysis; D011721:Pyrenes / Q000737:chemistry / Q000378:metabolism; D013296:Streptococcus pneumoniae / Q000235:genetics* / Q000502:physiology*
chemical_list: D005227:Fatty Acids; D005231:Fatty Acids, Unsaturated; D008081:Liposomes; D008563:Membrane Lipids; D010743:Phospholipids; D011721:Pyrenes; D004161:Diphenylhexatriene; C030984:pyrene