Isolation and characterization of a Lactobacillus plantarum bacteriophage, ΦJL-1, from a cucumber fermentation

A virulent Lactobacillus plantarum bacteriophage, ΦJL-1, was isolated from a commercial cucumber fermentation. The phage was specific for two related strains of L. plantarum, BI7 and its mutant (deficient in malolactate fermenting ability) MU45, which have been evaluated as starter cultures for controlled cucumber fermentation and as biocontrol microorganisms for minimally processed vegetable products. The phage genome of ΦJL-1 was sequenced to reveal a linear, double-stranded DNA (36.7 kbp). Sodium dodecyl sulfate-polyacryamide gel electrophoresis (SDS-PAGE) profiles indicated that ΦJL-1 contains six structural proteins (28, 34, 45, 50, 61, and 76 kDa). Electron microscopy revealed that the phage has an isometric head (59 nm in diameter), a long non-contractile tail (182 nm in length and 11 nm in width), and a complex base plate. The phage belongs to the Bradley group B1 or Siphoviridae family. One-step growth kinetics of the phage showed that the latent period was 35 min, the rise period was 40 min, and the average burst size was 22 phage particles/infected cell. Phage particles (90%) adsorbed to the host cells 20 min after infection. Calcium supplementation (up to 30 mM CaCl2) in MRS media did not affect the first cycle of phage adsorption, but promoted rapid phage propagation and cell lysis in the infection cycle subsequent to adsorption. The D values of ΦJL-1 at pH 6.5 were estimated to be 2.7 min at 70 °C and 0.2 min at 80 °C by a thermal inactivation experiment. Knowledge of the properties of L. plantarum bacteriophage ΦJL-1 may be important for the development of controlled vegetable fermentations.