Comparative genomics of the lactic acid bacteria

Lactic acid-producing bacteria are associated with various plant and animal niches and play a key role in the production of fermented foods and beverages. We report nine genome sequences representing the phylogenetic and functional diversity of these bacteria. The small genomes of lactic acid bacteria encode a broad repertoire of transporters for efficient carbon and nitrogen acquisition from the nutritionally rich environments they inhabit and reflect a limited range of biosynthetic capabilities that indicate both prototrophic and auxotrophic strains. Phylogenetic analyses, comparison of gene content across the group, and reconstruction of ancestral gene sets indicate a combination of extensive gene loss and key gene acquisitions via horizontal gene transfer during the coevolution of lactic acid bacteria with their habitats.

Use of RAPD-PCR as a method to follow the progress of starter cultures in sauerkraut fermentation

DNA fingerprinting methods were used to follow the progress of unmarked starter cultures in laboratory sauerkraut fermentations (1.2 and 13 l). Random prime PCR (RAPD-PCR) was used for strain-specific identification of Leuconostoc mesenteroides cultures. A comparative analysis of RAPD banding patterns for fermentation isolates and starter cultures was carried out using both genetically marked and unmarked cultures. While some variation in the RAPD patterns was observed, the results showed that the starter cultures dominated the fermentation during early heterofermentative stage for up to 5 days after the start of fermentation. Results from marked and unmarked starter cultures were confirmed by intergenic transcribed spacer (ITS)-PCR, and strain identify was confirmed by pulse field gel electrophoresis (PFGE) patterns. The results demonstrate the utility of RAPD to follow the progression of unmarked starter cultures of L. mesenteroides in sauerkraut fermentations.

Bacteriophage ecology in commercial sauerkraut fermentations

Knowledge of bacteriophage ecology in vegetable fermentations is essential for developing phage control strategies for consistent and high quality of fermented vegetable products. The ecology of phages infecting lactic acid bacteria (LAB) in commercial sauerkraut fermentations was investigated. Brine samples were taken from four commercial sauerkraut fermentation tanks over a 60- or 100-day period in 2000 and 2001. A total of 171 phage isolates, including at least 26 distinct phages, were obtained. In addition, 28 distinct host strains were isolated and identified as LAB by restriction analysis of the intergenic transcribed spacer region and 16S rRNA sequence analysis. These host strains included Leuconostoc, Weissella, and Lactobacillus species. It was found that there were two phage-host systems in the fermentations corresponding to the population shift from heterofermentative to homofermentative LAB between 3 and 7 days after the start of the fermentations. The data suggested that phages may play an important role in the microbial ecology and succession of LAB species in vegetable fermentations. Eight phage isolates, which were independently obtained two or more times, were further characterized. They belonged to the family Myoviridae or Siphoviridae and showed distinct host ranges and DNA fingerprints. Two of the phage isolates were found to be capable of infecting two Lactobacillus species. The results from this study demonstrated for the first time the complex phage ecology present in commercial sauerkraut fermentations, providing new insights into the bioprocess of vegetable fermentations.