Isolation and characterization of a virulent Lactobacillus sanfranciscensis bacteriophage and its impact on microbial population in sourdough.

Thirty-five sourdough samples used for sweet and salted Italian baked products were checked for the presence of a virus active on Lactobacillus sanfranciscensis species. One phage, named EV3, was isolated and its phenotypic and genotypic features were investigated. It belonged to the Siphoviridae family (morphotype B1); its life cycle at 25 degrees C lasted 3 h with a burst size of about 30 viral particles per infected cell. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) showed one major structural protein of 35 kDa and four minor proteins. The genome, approximately 32 kb long, was a double-stranded linear DNA molecule with a pac-type system. Phage spreading into sourdough did not adversely affect acidification and volume increase of the dough neither lactobacilli counts; the propagation of viral particles was shown to be hindered. This is the first report of the isolation of a L. sanfranciscensis phage.