Surface layer variations affecting phage adsorption on seven Lactobacillus helveticus strains

Abstract – In a previous work it was demonstrated that Lactobacillus helveticus CNRZ 892 strain is covered by a protein of the S-layer type. The gene encoding for this protein was isolated and sequenced and it was shown that the central region of S-layer protein of this strain plays a role of receptor for the virulent phage CNRZ 832-B1. Here we present data of S-layer encoding genes isolated from seven L. helveticus strains showing a different sensitivity to the CNRZ 832-B1 phage. The sequence analysis of genes isolated from the phage sensitive strains (ATCC 12046, ATCC 15009 and CNRZ 303) showed, in the central part, an identical nucleotide sequence with that obtained from CNRZ 892. On the contrary we found in S-layer gene sequences of the phage resistant strains, unable to adsorb the phage CNRZ 832-B1 (CNRZ 35, I60, HLM1 and M696), point mutations localised in the same region as the CNRZ 892 isogenic mutants. These data suggest that the change of one or more amino acids in this area seems to affect phage adsorption. Key words: Lactobacillus helveticus, phage receptor, surface layer, dairy products.