The genus Lactobacillus comprises 261 species (at March 2020) that are extremely diverse at phenotypic, ecological and genotypic levels. This study evaluated the taxonomy of Lactobacillaceae and Leuconostocaceae on the basis of whole genome sequences. Parameters that were evaluated included core genome phylogeny, (conserved) pairwise average amino acid identity, clade-specific signature genes, physiological criteria and the ecology of the organisms. Based on this polyphasic approach, we propose reclassification of the genus Lactobacillus into 25 genera including the emended genus Lactobacillus , which includes host-adapted organisms that have been referred to as the Lactobacillus delbrueckii group, Paralactobacillus and 23 novel genera for which the names Holzapfelia, Amylolactobacillus, Bombilactobacillus, Companilactobacillus, Lapidilactobacillus, Agrilactobacillus, Schleiferilactobacillus, Loigolactobacilus, Lacticaseibacillus, Latilactobacillus, Dellaglioa, Liquorilactobacillus, Ligilactobacillus, Lactiplantibacillus, Furfurilactobacillus, Paucilactobacillus, Limosilactobacillus, Fructilactobacillus, Acetilactobacillus, Apilactobacillus, Levilactobacillus, Secundilactobacillus and Lentilactobacillus are proposed. We also propose to emend the description of the family Lactobacillaceae to include all genera that were previously included in families Lactobacillaceae and Leuconostocaceae . The generic term ‘lactobacilli’ will remain useful to designate all organisms that were classified as Lactobacillaceae until 2020. This reclassification reflects the phylogenetic position of the micro-organisms, and groups lactobacilli into robust clades with shared ecological and metabolic properties, as exemplified for the emended genus Lactobacillus encompassing species adapted to vertebrates (such as Lactobacillus delbrueckii , Lactobacillus iners , Lactobacillus crispatus , Lactobacillus jensensii, Lactobacillus johnsonii and Lactobacillus acidophilus ) or invertebrates (such as Lactobacillus apis and Lactobacillus bombicola ).

An expert panel was convened in September 2019 by The International Scientific Association for Probiotics and Prebiotics (ISAPP) to develop a definition for fermented foods and to describe their role in the human diet. Although these foods have been consumed for thousands of years, they are receiving increased attention among biologists, nutritionists, technologists, clinicians and consumers. Despite this interest, inconsistencies related to the use of the term ‘fermented’ led the panel to define fermented foods and beverages as “foods made through desired microbial growth and enzymatic conversions of food components”. This definition, encompassing the many varieties of fermented foods, is intended to clarify what is (and is not) a fermented food. The distinction between fermented foods and probiotics is further clarified. The panel also addressed the current state of knowledge on the safety, risks and health benefits, including an assessment of the nutritional attributes and a mechanistic rationale for how fermented foods could improve gastrointestinal and general health. The latest advancements in our understanding of the microbial ecology and systems biology of these foods were discussed. Finally, the panel reviewed how fermented foods are regulated and discussed efforts to include them as a separate category in national dietary guidelines.

Lactobacillus species are found in nutrient-rich habitats associated with food, feed, plants, animals and humans. Due to their economic importance, the metabolism, genetics and phylogeny of lactobacilli have been extensively studied. However, past research primarily examined lactobacilli in experimental settings abstracted from any natural history, and the ecological context in which these bacteria exist and evolve has received less attention. In this review, we synthesize phylogenetic, genomic and metabolic metadata of the Lactobacillus genus with findings from fine-scale phylogenetic and functional analyses of representative species to elucidate the evolution and natural history of its members. The available evidence indicates a high level of niche conservatism within the well-supported phylogenetic groups within the genus, with lifestyles ranging from free-living to strictly symbiotic. The findings are consistent with a model in which host-adapted Lactobacillus lineages evolved from free-living ancestors, with present-day species displaying substantial variations in terms of the reliance on environmental niches and the degree of host specificity. This model can provide a framework for the elucidation of the natural and evolutionary history of Lactobacillus species and valuable information to improve the use of this important genus in industrial and therapeutic applications.