The Genus Lactobacillus: A Taxonomic Update

Lactic Acid Bacteria (LAB) are a functional group of microorganisms comprising Gram-positive, catalase negative bacteria that produce lactic acid as the major metabolic end-product of carbohydrate fermentation. Among LAB, Lactobacillus is the genus including a high 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. From a taxonomic point of view, the genus Lactobacillus includes at present (October 2012), 152 validly described species, and it belongs to the family Lactobacillaceae together with genus Pediococcus, with whom it is phylogenetically intermixed. The updated phylogenetic analysis based on 16S rRNA gene sequence revealed that the family is divided into 15 groups of three or more species, 4 couples and 10 single lines of descents. In addition, other taxonomically relevant information for Lactobacillus species was collected. This study aims at updating the taxonomy of the genus Lactobacillus, presenting the phylogenetic structure of the Lactobacillaceae and discussing the clusters as possible nuclei of genera to be described in the future. It is expected that scientists and producers in the field of probiotics could benefit from information reported here about the correct identification procedures and nomenclature of beneficial strains of lactobacilli.