The bacteriophage kh receptor of Lactococcus lactis subsp. cremoris KH is the rhamnose of the extracellular wall polysaccharide

Abstract

A receptor for bacteriophages of lactic acid bacteria, including Lactococcus lactis subsp. cremoris KH, was found on the cell wall and not on the cell membrane, as determined by a phase-binding assay of sodium dodecyl sulfate- and mutanolysin-treated cell walls. The cell wall carbohydrates of L. lactis subsp. cremoris KH were analyzed by gas chromatography and mass spectrometry and found to contain rhamnose, galactose, glucose and N-acetylglucosamine. Similar analysis of mutants that were reduced in the ability to bind phages kh, 643, c2, ml3, and l indicated that galactose was essential for binding all phages. In addition, rhamnose was required for binding phages kh and ml3. Inhibition studies of phage binding by using two different lectins with a specificity for galactose indicated that phase kh may not bind directly to galactose. Rather, galactose may be an essential structural component located in the vicinity of the receptor. Incubation of any of the five phages with rhamnose or of phage kh with purified cell walls inactivated the phages. Inactivation required divalent cations and was irreversible. Inactivation of phages was stereospecific for rhamnose, as neither L-(+)- nor D-(-)-fucose (the stereoisomers of rhamnose) inhibited the phage. Furthermore, phage infection of a culture was completely inhibited by the addition of rhamnose to the medium. Therefore, the receptor for phage kh appears to be a rhamnose component of the extracellular wall polysaccharide.