MOLECULAR ARCHITECTURE OF THE LACTOCOCCAL CELL-SURFACE AS IT RELATES TO IMPORTANT INDUSTRIAL PROPERTIES

From an industrial perspective there are a number of important propert ies of lactococci that are either carried on, or are controlled and re gulated by, the cell surface e.g. phage adsorption, exopolysaccharide production, cell aggregation/sedimentation, cell autolysis and the tra nslocation of foreign DNA. Lactococcus lactis subsp. cremoris strain E 8 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 involve d in phage adsorption. Genetically, the two strains were found to be v ery 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 conta ining, Asp, Glu, Lys and Ala in molar ratio of 1:1:1:2, respectively. There were, however, significantly quantitative differences in the lev els of monosaccharide in accessory polysaccharide of the two strains; the parent strain contained 15-fold more galactose and 3-fold more glu cosamine. In order to identify the components of the cell wall involve d in phage adsorption, the cell walls from the parent strain (strain E 8) were subjected to carious chemical and enzymatical treatments befor e testing their ability to adsorb different phages. The result indicat ed that the essential component of the phage receptor in the cell wall of Lc. lactis subsp. cremoris strain E8 was carbohydrate in nature an d was covalently linked to the peptidoglycans. Lectin binding experime nts revealed that galactose adn glucosamine were required for the adso rption of phages. An electron microscopic study of the interaction bet ween the phages and their host showed that phages adsorb to a limited number of receptor sites which were distributed over the entire cell e nvelope.