The cell surface polysaccharides and membrane protein required for bacteriophage infection of Lactococcus lactis

Graduation date: 1992The bacteriophage receptor of lactococci was found on the cell\ud walls. A carbohydrate analysis of the cell walls from phage-resistant\ud mutants of L. lactis subsp. cremoris KR with reductions in phage binding\ud indicated that a loss of galactose correlated with a loss in binding\ud and infection of all phage tested: kh, 643, 1, c2 and m13. In addition,\ud a loss of rhamnose correlated with a reduction in binding of phages kh\ud and m13. Inhibition studies of phage binding by lectins specific to\ud galactose suggested that phage kh does not bind directly to galactose.\ud Incubation of any of the five phages with 0.5M rhamnose, but not\ud galactose, completely inactivated the phage. Addition of rhamnose to\ud a growing liquid culture infected with all five phages or with phage kh\ud inhibited the infection. This suggested that the receptor of phage for\ud L. lactis subsp. cremoris KR is the rhamnose of the extracellular\ud polysaccharide.\ud In a similar analysis, phage skl was found to require rhamnose and\ud glucose of the extracellular polysaccharide of L. lactis subsp. lactis C2 for binding. The lectin studies suggests that phage ski does not\ud bind directly to glucose. The partial inhibition of phage ski infection\ud when rhamnOse, but not glucose, was added to a liquid culture suggests\ud that phage ski binds directly to the rhamnose.\ud The phage-resistant mutants isolated from superinfections of L.\ud lactis subsp. lactis C2 with phage c2 did not form plaques, but bound\ud normally to phage c2. The sensitivity of these mutants to phage ski was\ud also reduced significantly. In another analysis of mutants isolated\ud from superinfections with phage skl, none formed plaques with either\ud phage c2 or skl, but bound normally to both phages. The mutations\ud affected the cell membrane, as the membrane from wild type, but not from\ud phage-resistant cells, inactivated phage c2. The phage-inactivation\ud activity was eliminated by treatment with a protease, but not a\ud glycosidase. The partially purified phage-inactivating protein was\ud found to have an apparent molecular weight of 350,000 under nondenaturing\ud conditions and an apparent subunit size of 32 kDa. It is\ud proposed that a multimeric complex of the 32 kDa protein is required for\ud phage c2 and skl infection of strain C2