Systematics of Lactic Acid Bacteria

Lactic acid bacteria (LAB) are a functional group which, from a taxonomical viewpoint, is distributed in different genera and families, belonging mainly to the order Lactobacillales. The Family Lactobacillaceae includes the largest majority of GRAS species and, at present, about 200 species are ascribed to the genus Lactobacillus suggesting a diversity much larger than that recognized when analyzing only the species of applied importance. Delineation of taxonomic ranks is conventionally based on phylogenetic analysis, which does not correlate with metabolic differences. The availability of genome sequences allows to depict the evolutionary history of the different taxa more precisely than previously. In the near future, a major impact on taxonomic procedures is expected thanks to the databases and software accessibility.

Lactobacillaceae is the most numerous and heterogeneous family, as about 180 species are recognized. From an applied viewpoint, families Lactobacillaceae and Streptococcaceae represent the two most important lineages since they encompass the highest number of commercialized lactic acid bacteria (LAB). Lactobacillaceae includes the highest number of GRAS species (Generally Recognized As Safe) and many strains are among the most important bacteria in food microbiology and human nutrition due to their contribution to fermented food production or their use as probiotics. Taxonomic procedures have always evolved dependently of technology advances, as the introduction of innovative methods has always provided new opportunities for prokaryotic systematics. Genome sequence data can be retrieved from a number of databases. Some online databases and tools, which can be employed to gain taxonomic data either from entire genomes or single sequences, are: Comprehensive Microbial Resource (CMR), DNA Bank Network, and Global Genome Biodiversity Network.