Taxonomy of lactic acid bacteria: Historical background and prospects

Abstract

“Lactic acid bacteria” has been used as a general term for a group of Gram-positive, catalase-negative bacteria that produce lactic acid as a major metabolite through sugar fermentation. The genera of this group have been defined by cell morphology and fermentation type, and the species has been described by sugar fermentation patterns as well as growth temperature and lactic acid isomers produced. Until Bergey’s manual of systematic bacteriology (1st edition) Vol. 2 published in 1986, lactic acid cocci were classified into the genera Streptococcus and Pediococcus for homofermentative lactic acid fermentation, the genus Leuconostoc for heterofermentative fermentation, and the genus Lactobacillus for rod-shaped lactic acid bacteria. The phylogenetic classification based on the 16S rRNA gene was used for the reclassification of the known species, and new genera were also assigned to newly isolated lactic acid bacteria. The second edition of the manual published in 2009 established the order Lactobacillales, including 33 genera in 6 families, and the number has now increased to 70 genera. Hierarchical structure of the lactic acid bacteria has been completed by the phylogenetic characterization based on the 16S rRNA sequences accompanying with the phenotypic properties. However, now the new challenges using phylogenomic analyses using whole genome sequences are emerging to evaluate the current taxonomic structure. We must catch up the new genomic era in the prokaryote taxonomy community.