Comparative Genomics of Lactobacillus brevis Reveals a Significant Plasmidome Overlap of Brewery and Insect Isolates.

Lactobacillus (L.) brevis represents a versatile, ubiquitistic species of lactic acid bacteria, occurring in various foods, as well as plants and intestinal tracts. The ability to deal with considerably differing environmental conditions in the respective ecological niches implies a genomic adaptation to the particular requirements to use it as a habitat beyond a transient state. Given the isolation source, 24 L. brevis genomes were analyzed via comparative genomics to get a broad view of the genomic complexity and ecological versatility of this species. This analysis showed L. brevis being a genetically diverse species possessing a remarkably large pan genome. As anticipated, it proved difficult to draw a correlation between chromosomal settings and isolation source. However, on plasmidome level, brewery- and insect-derived strains grouped into distinct clusters, referable to a noteworthy gene sharing between both groups. The brewery-specific plasmidome is characterized by several genes, which support a life in the harsh environment beer, but 40% of the brewery plasmidome were found in insect-derived strains as well. This suggests a close interaction between these habitats. Further analysis revealed the presence of a truncated horC cluster version in brewery- and insect-associated strains. This disproves horC, the major contributor to survival in beer, as brewery isolate specific. We conclude that L. brevis does not perform rigorous chromosomal changes to live in different habitats. Rather it appears that the species retains a certain genetic diversity in the plasmidome and meets the requirements of a particular ecological niche with the acquisition of appropriate plasmids.