Abstract

Abstract From an industrial perspective there are a number of important properties of lactococci that are either carried on, or are controlled and regulated by, the cell surface e.g. phage adsorption, exopolysaccharide production, cell aggregation/sedimentation, cell autolysis and the translocation of foreign DNA. Lactococcus lactis subsp. cremoris strain E8 and its spontaneous phage-resistant variant strain 398 were used as a model system to study the molecular architecture of the lactococcal cell surface and to identify the cell wall components that are involved in phage adsorption. Genetically, the two strains were found to be very closely related as determined by the comparison of chromosomal DNA and plasmid profiles. Two major cell wall components of both strains were the accessory polysaccharides and peptidoglycan, the latter containing, Asp, Glu, Lys and Ala in molar ratio of 1:1:1:2, respectively. There were, however, significant quantitative differences in the levels of monosaccharide in accessory polysaccharide of the two strains; the parent strain contained 15-fold more galactose and 3-fold more glucosamine. In order to identify the components of the cell wall involved in phage adsorption, the cell walls from the parent strain (strain E8) were subjected to various chemical and enzymatical treatments before testing their ability to adsorb different phages. The result indicated that the essential component of the phage receptor in the cell wall of Lc. lactis subsp. cremoris strain E8 was carbohydrate in nature and was covalently linked to the peptidoglycans. Lectin binding experiments revealed that galactose and glucosamine were required for the adsorption of phages. An electron microscopic study of the interaction between the phages and their host showed that phages adsorb to a limited number of receptor sites which were distributed over the entire cell envelope.

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