A protein which masks galactose receptor mediated phage susceptibility in Lactococcus lactis subsp. lactis MPL56

Abstract

A 28.5‐kb plasmid, isolated from Lactococcus lactis subsp. lactis MPL56, causes complete inhibition of four lactococcal phages. Cell wall characteristics of wild‐type strain MPL56 were compared with its 28.5 kb plasmid‐cured, phage‐sensitive derivative MPL56‐22. After proteolytic enzyme treatments, adsorption of phages occurred at high levels, an example is 94.6–98.5% in MPL56 cells. Analysis of cell wall extracts of MPL56‐22 by sodium dodecyl sulphate–polyacrylamide gel electrophoresis (SDS–PAGE) indicated that the only difference between strains was the 55.4 kDa band in protein patterns of MPL56. Adsorption of the four phages was completely inhibited when MPL56‐22 cells were subjected to SDS, Triton‐X‐100, HCl and NaOH treatments. Lectins that were specific for glucose/mannose and N‐acetylglucosamine did not prevent adsorption of phages in cell wall extracts of MPL 56‐22. However a lectin specific for galactose (MCA; Momordica charantia) completely inhibited adsorption of these phages in cell wall extracts of MPL56‐22. HPLC patterns of cell wall carbohydrates of MPL56‐22 and its HCl treated preparations showed that the most prevalent difference was the galactose on untreated MPL56‐22 cell wall chromatograms.

Lactic Acid Bacteria Resistance to Bacteriophage and Prevention Techniques to Lower Phage Contamination in Dairy Fermentation

“…The best documented plasmid-encoded mechanisms of inhibition of phage adsorption rely on either direct synthesis of cell surface antigens or the production of extracellular carbohydrates. Of the two modes of action, the former reveals phage specificity, whereas the latter seems to restrict access to the bacterial cell for various harmful factors, including bacteriophages [25]. Studies carried by Tuncer and Akcelic demonstrated that a 28.5-kb plasmid, isolated from L. lactis subsp.…”

“…Studies carried by Tuncer and Akcelic demonstrated that a 28.5-kb plasmid, isolated from L. lactis subsp. lactis MPL56, causes complete inhibition of four lactococcal phages due to the production of a 55.4-kDa protein [25]. The protein exhibits similarity to lectins, a group of proteins that adsorb to specific monosaccharide components of polysaccharides in the cell wall, hence, impairing specific recognition of the phage receptor sites by these four phages.…”

“…The protein exhibits similarity to lectins, a group of proteins that adsorb to specific monosaccharide components of polysaccharides in the cell wall, hence, impairing specific recognition of the phage receptor sites by these four phages. Thus, this plasmidencoded 55.4-kDa protein shields specifically the galactose-containing receptor rather than interacts with the phage, in other words, the bacterial lectin and the phage RBP compete for the receptor [25]. Another example of physical masking of the receptor is the plasmidmediated production of extracellular carbohydrates, called exopolysaccharides (EPS) [26].…”

“…On the other hand, polysaccharides have an impact on the properties of dairy products, like: texture, viscosity and smoothness of mouthfeel. Thereby, application of EPS-producing phage-resistant strains might be limited to a narrow range of dairy products [25][26].…”