IMPROVED PROCESSES FOR CUCUMBERS, CABBAGE, SWEETPOTATOES, AND PEPPERS TO MAKE HIGH QUALITY, NUTRITIOUS PRODUCTS AND REDUCE POLLUTION
Location: Food Science Research
Title: Bacteriophage ecology in a commercial cucumber fermentation
Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 24, 2012
Publication Date: December 1, 2012
Citation: Lu, Z., Perez Diaz, I.M., Hayes, J.S., Breidt, F. 2012. Bacteriophage ecology in a commercial cucumber fermentation. Applied and Environmental Microbiology. 78(24):8571-8578.
Interpretive Summary: The successful application of commercial low salt fermentations requires the addition of a lactic acid bacterium culture to initiate the conversion of sugars to lactic acid quickly after brining fresh cucumbers. Viruses capable of attacking lactic acid bacteria may be capable of preventing the fermentation, which could result in low quality malodorous preserves. Thus, the objective of this research was to investigate the population of viruses capable of infecting bacteria present in commercial cucumber fermentation. Ten percent of the bacterial isolates from the commercial fermentation were sensitive to viruses. Seventeen distinct viruses were isolated from the fermentation. Some viruses were able to attack a specific bacterial species and a few were able to attack more than one bacterial genus, indiscriminately. Thus, it was understood that viruses naturally present in commercial fermentations could cause significant mortality to the lactic acid bacteria population responsible for leading cucumber fermentation, which is essential in preserving the fruits.
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 de-Man-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.