Bacteriophage Ecology in a Commercial Cucumber Fermentation

To reduce high-salt waste from cucumber fermentations, low-salt fermentations are under development. These fermentations may require the use of starter cultures to ensure normal fermentations. Because potential phage infection can cause starter culture failure, it is important to understand phage ecology in the fermentations. This study investigated the phage ecology in a commercial cucumber fermentation. Brine samples taken from a fermentation tank over a 90-day period were plated onto deMan-Rogosa-Sharpe agar plates. A total of 576 lactic acid bacterial isolates were randomly selected to serve as potential hosts for phage isolation. Filtered brine served as a phage source. Fifty-seven independent phage isolates were obtained, indicating that 10% of the bacterial isolates were sensitive to phage attack. Phage hosts include Lactobacillus brevis (67% of all hosts), Lactobacillus plantarum (21%), Weissella paramesenteroides, Weissella cibaria, and Pediococcus ethanolidurans. Nearly 50% of phages were isolated on day 14, and the majority of them attacked L. brevis. Some phages had a broad host range and were capable of infecting multiple hosts in two genera. Other phages were species specific or strain specific. About 30% of phage isolates produced turbid pinpoint plaques or only caused reduced cell growth on the bacterial lawns. Six phages with distinct host ranges were characterized. The data from this study showed that abundant and diverse phages were present in the commercial cucumber fermentation, which could cause significant mortality to the lactic acid bacteria population. Therefore, a phage control strategy may be needed in low-salt cucumber fermentations. L ike most other vegetable fermentations, cucumber fermentations are driven by a variety of lactic acid bacteria (LAB) naturally present on vegetables. The metabolic activities of LAB determine the quality and safety of the final fermentation products (30). Vegetable fermentation is a dynamic biochemical system in which the chemical composition and microbial ecology are continuously changing. Those changes can be influenced by many physical, chemical, and biological factors such as temperature, pH, salt concentration, and the microbiota (bacteria, fungi, bacteriophages, etc.) present on vegetables (5, 12). The presence of diverse phages against LAB in vegetable fermentations can potentially cause significant mortality to LAB, thereby influencing the number, type, and succession of LAB populations during the fermentation, as well as the type, rate, and extent of carbohydrate metabolism. Phages are ubiquitous in nature. Several studies showed that a diverse phage community was present in vegetable fermentations (2, 19, 20, 36, 37). We previously reported the phage ecology in commercial sauerkraut fermentations (20), and the genome sequences of two LAB phages (JL-1 and 1-A4, infecting Lactobacillus plantarum and Leuconostoc mesenteroides, respectively) isolated from vegetable fermentations (17, 18). Although several LAB phages active againstL. plantarumandPediococcussp. have been isolated from commercial cucumber fermentations (19, 36), phage ecology in commercial cucumber fermentations has not been investigated. In the pickle industry, cucumbers are typically fermented in a brinecontaining6%NaClinopen-toptanksthatareabout40,000 liters in volume (5). In cold climates additional salt, up to 12%, is