Pk. Gopal et Ki. Reilly, MOLECULAR ARCHITECTURE OF THE LACTOCOCCAL CELL-SURFACE AS IT RELATES TO IMPORTANT INDUSTRIAL PROPERTIES, International dairy journal, 5(8), 1995, pp. 1095-1111
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.