Characterization of a new virulent phage infecting the lactic acid bacterium Oenococcus oeni

• The study reports on phages preying on Oenococcus oeni in the enological environment.
• phiOE33 PA which is only capable to follow a lytic cycle was characterized.
• Persistence capacities of phiOE33 PA in wine were assessed.
• qPCR assays were designed to survey the phage levels in wine samples.
• Results show that noninfectious phage particles persist in the medium.

ΦOE33PA is a new virulent siphophage infecting Oenococcus oeni that was isolated from a red wine collected in Pauillac (France). Although the phage could not lysogenize its host, a conserved sequence within the integrase genes harbored by oenophages could be detected, and corresponded to a B-type integrase. The phage host range encompassed ten out of the 38 O. oeni strains tested. One-step growth kinetics revealed latent and burst periods of 4 and 5 h, respectively, with a burst size of about 45 plaque-forming units per infected cell. The phage had a distinctive restriction profile when compared with Φ10 MC, another B-type oenophage previously isolated in our laboratory. Incubation in wine could inactivate high-titer suspensions of ΦOE33PA in a short time at room temperature. However, encapsidated phage DNA could still be detected by real time PCR, and these non-infectious viruses dominated the wine samples showing that direct enumeration of phages in wine samples using the double-layer agar technique only informs about the quantity of residual infectious phages. Kinetics studies throughout the fermentation using both qPCR as well as plating should now provide reliable understanding of the phage dynamics during wine making.