Genome-level comparisons provide insight into the phylogeny and metabolic diversity of species within the genus Lactococcus.

BACKGROUND: The genomic diversity of different species within the genus Lactococcus and the relationships between genomic differentiation and environmental factors remain unclear. In this study, type isolates of ten Lactococcus species/subspecies were sequenced to assess their genomic characteristics, metabolic diversity, and phylogenetic relationships. RESULTS: The total genome sizes varied between 1.99 (Lactococcus plantarum) and 2.46 megabases (Mb; L. lactis subsp. lactis), and the G + C content ranged from 34.81 (L. lactis subsp. hordniae) to 39.67% (L. raffinolactis) with an average value of 37.02%. Analysis of genome dynamics indicated that the genus Lactococcus has an open pan-genome, while the core genome size decreased with sequential addition at the genus and species group levels. A phylogenetic dendrogram based on the concatenated amino acid sequences of 643 core genes was largely consistent with the phylogenetic tree obtained by 16S ribosomal RNA (rRNA) genes, but it provided a more robust phylogenetic resolution than the 16S rRNA gene-based analysis. CONCLUSIONS: Comparative genomics indicated that species in the genus Lactococcus had high degrees of diversity in genome size, gene content, and carbohydrate metabolism. This may be important for the specific adaptations that allow different Lactococcus species to survive in different environments. These results provide a quantitative basis for understanding the genomic and metabolic diversity within the genus Lactococcus, laying the foundation for future studies on taxonomy and functional genomics.

Assessment of the bacterial and fungal diversity in home-made yoghurts of Xinjiang, China by pyrosequencing.

BACKGROUND: The aim of this study was to gain a deeper knowledge of the bacterial and fungal community diversity in local home-made yoghurts from Zhaosu and Tekesi counties, Xinjiang, China, where a relatively high proportion of the ethnic minority population resides. RESULTS: The bacterial and fungal community diversity in 22 home-made yoghurt samples was analyzed by pyrosequencing. This approach revealed the presence of six bacterial and two fungal phyla, comprising 69 bacterial and 20 fungal genera respectively, among all samples. Firmicutes and Ascomycota were the dominant phyla and Lactobacillus and Saccharomyces the predominant genera of bacteria and fungi respectively. Based on redundancy analysis, the bacterial diversity in samples from the two counties differed mainly because of eight responsive operational taxonomic units of Lactobacillus. However, no obvious difference existed in the fungal population of samples from the two counties. CONCLUSION: The results indicated that the microbial community of home-made yoghurts varied with their geographical origin and manufacturing process. The study showed that pyrosequencing could provide a better understanding of microbiological diversity as well as useful information for future studies on the selection of starter cultures for yoghurts.