2010 Annual Report
1a.Objectives (from AD-416)
To isolate the predominant bacteria present in commercial cucumber fermentations and evaluate their ability to serve as host for bacteriophages possibly present in the same environment.
1b.Approach (from AD-416)
Brine samples of at least two commercial cucumber fermentations will be collected. Samples will be spiral plated on MRS and VRBG agars to select for lactic acid bacteria and enterobacteriaceae. Selected colonies will be isolated and screened for their sensitivity to bacteriophages present in the brine samples. Bacterial hosts and bacteriophages will be identified by 16S rRNA sequencing and electronic microscopy, respectively.
This project is related to Objective 1 of this in-house project: develop reduced salt fermentation procedures for cucumbers and cabbage that will consistently produce vegetables with firm texture and appropriate flavor. The bacteriophage ecology in commercial cucumber fermentation was studied with the aim of applying this knowledge for the selection of a starter culture for cucumber fermentation.
Brine samples were collected over a 90-day period and served as the source for the isolation of approximately 700 bacterial colonies belonging to the lactic acid bacteria (LAB) and enterobacteriacea groups. While isolates served as potential hosts, the filtered brine samples were used as phage sources. A total of 57 independent phage isolates against LAB were obtained, primarily from the seventh and fourteenth days of fermentation, in which the hosts reached maximum counts (109 CFU/ml). Representative LAB phages from each sampling day were characterized by electron micrographs. The majority of the phages were identified as members of the Myoviridae or Siphoviridae families, except for one phage belonging to the Podoviridae family. These phages showed distinct host ranges, protein profiles, and DNA fingerprints. Phage hosts were identified by 16S rDNA sequence analyses. LAB hosts include Weissella paramesenteroides, Weissella cibaria, Lactobacillus brevis, and Lactobacillus plantarum. Although, enteric phages and specific hosts have not been characterized, the LAB phages data suggest that a complex phage ecology with multiple isolates from a variety of families seems to be present in commercial cucumber fermentations, suggesting that phages may play an important role in the succession of LAB species in vegetable fermentations.
Progress on this project was made as a team effort, thus communication via e-mail and phone calls was frequent. Discussion meetings were scheduled as necessary.