Lactobacillus
Lactobacillus is a genus of gram-positive bacteria within the Lactobacillaceae family. Members of the genus are aerotolerant anaerobes or microaerophilic, rod-shaped, and do not form endospores. Until 2020, the genus Lactobacillus comprised 261 phylogenetically, ecologically, and metabolically diverse species; a taxonomic revision of the genus reassigned many former Lactobacillus species to 25 genera.
Lactobacillus species constitute a significant component of the human and animal microbiota at a number of body sites, such as the digestive system and female genital system. ILactobacillus species are normally a major part of the vaginal microbiota. Lactobacillus forms biofilms in the vaginal and gut microbiota, allowing them to persist in harsh environmental conditions and maintain ample populations. Lactobacillus exhibits a mutualistic relationship with the human body, as it protects the host against potential invasions by pathogens, and in turn, the host provides a source of nutrients. Lactobacilli are among the most common probiotics found in food such as yogurt, and the bacteria are diverse in their application in maintaining well-being, by helping to treat diarrhea, vaginal infections, and skin disorders such as eczema.
Metabolism
Lactobacilli are homofermentative, i.e., hexoses are metabolized by glycolysis to lactate as the major end product, or heterofermentative, i.e., hexoses are metabolized by the phosphoketolase pathway to lactate, CO2, and acetate or ethanol as major end products. Most lactobacilli are aerotolerant and some species respire if heme and menaquinone are present in the growth medium. Aerotolerance of lactobacilli is manganese-dependent and has been explored in Lactiplantibacillus plantarum ''. Lactobacilli generally do not require iron for growth.The Lactobacillaceae are the only family of the lactic acid bacteria that includes homofermentative and heterofermentative organisms; in the Lactobacillaceae, homofermentative or heterofermentative metabolism is shared by all strains of a genus. Lactobacillus species are all homofermentative, do not express pyruvate formate lyase, and most species do not ferment pentoses. In L. crispatus, pentose metabolism is strain specific and acquired by lateral gene transfer.
Genomes
The genomes of lactobacilli are highly variable, ranging in size from 1.2 to 4.9 Mb. Accordingly, the number of protein-coding genes ranges from 1,267 to about 4,758 genes. Even within a single species, there can be substantial variation. For instance, strains of L. crispatus have genome sizes ranging from 1.83 to 2.7 Mb, or 1,839 to 2,688 open reading frames. Lactobacillus contains a wealth of compound microsatellites in the coding region of the genome, which are imperfect and have variant motifs. Many lactobacilli also contain multiple plasmids. A recent study has revealed that plasmids encode the genes which are required for adaptation of lactobacilli to the given environment.Species
The genus Lactobacillus comprises the following species:- Lactobacillus acetotolerans Entani et al. 1986
- Lactobacillus acidophilus Hansen and Mocquot 1970
- Lactobacillus agrestimuris Afrizal et al. 2023
- Lactobacillus amylolyticus Bohak et al. 1999
- Lactobacillus amylovorus Nakamura 1981
- Lactobacillus apis Killer et al. 2014
- Lactobacillus bombicola Praet et al. 2015
- Lactobacillus colini Zhang et al. 2017
- Lactobacillus corticus Tohno et al. 2021
- Lactobacillus crispatus Moore and Holdeman 1970
- Lactobacillus delbrueckii Beijerinck 1901
- Lactobacillus equicursoris Morita et al. 2010
- Lactobacillus fornicalis Dicks et al. 2000
- Lactobacillus gallinarum Fujisawa et al. 1992
- Lactobacillus gasseri Lauer and Kandler 1980
- Lactobacillus gigeriorum Cousin et al. 2012
- Lactobacillus hamsteri Mitsuoka and Fujisawa 1988
- Lactobacillus helsingborgensis Olofsson et al. 2014
- Lactobacillus helveticus Bergey et al. 1925
- Lactobacillus hominis Cousin et al. 2013
- Lactobacillus huangpiensis Li and Gu 2022
- Lactobacillus iners Falsen et al. 1999
- Lactobacillus intestinalis Fujisawa et al. 1990
- Lactobacillus isalae Eilers et al. 2023
- Lactobacillus jensenii Gasser et al. 1970
- Lactobacillus juensis Jiang and Gu 2024
- Lactobacillus johnsonii Fujisawa et al. 1992
- Lactobacillus kalixensis Roos et al. 2005
- Lactobacillus kefiranofaciens Fujisawa et al. 1988
- Lactobacillus kimbladii Olofsson et al. 2014
- Lactobacillus kitasatonis Mukai et al. 2003
- Lactobacillus kullabergensis Olofsson et al. 2014
- Lactobacillus laiwuensis Li and Gu 2022
- Lactobacillus leichmannii Bergey et al. 1923
- Lactobacillus melliventris Olofsson et al. 2014
- Lactobacillus mulieris Rocha et al. 2020
- Lactobacillus nasalidis Suzuki-Hashido et al. 2021
- Lactobacillus panisapium Wang et al. 2018
- Lactobacillus paragasseri Tanizawa et al. 2018
- Lactobacillus pasteurii Cousin et al. 2013
- Lactobacillus porci Kim et al. 2018
- Lactobacillus psittaci Lawson et al. 2001
- Lactobacillus rhamnosus Collins et al. 1989
- Lactobacillus rizhaonensis Jiang and Gu 2024
- Lactobacillus rodentium Killer et al. 2014
- Lactobacillus rogosae Holdeman and Moore 1974
- Lactobacillus taiwanensis Wang et al. 2009
- Lactobacillus timonensis Afouda et al. 2017
- Lactobacillus ultunensis Roos et al. 2005
- Lactobacillus xujianguonis Meng et al. 2020
- Lactobacillus xylocopicola Kawasaki et al. 2024
Taxonomy
| Genus | Meaning of the genus name | Properties of the genus |
| Lactobacillus | Rod-shaped bacillus from milk | Type species: L. delbrueckii. Homofermentative with strain-specific ability to ferment pentoses, thermophilic, vancomycin-sensitive, adapted to vertebrate or insect hosts. |
| Holzapfelia | Wilhelm Holzapfel's lactobacilli | Type species: H. floricola. Homofermentative, vancomycin sensitive, unknown ecology but likely host-adapted. |
| Amylolactobacillus | Starch-degrading lactobacilli | Type species: A. amylophilus. Homofermentative, vancomycin sensitive, extracellular amylases are frequent, unknown ecology but likely host-adapted. |
| Bombilactobacillus | Lactobacilli from bees and bumblebees | Type species: B. mellifer. Homofermentative, thermophilic, vancomycin resistant, small genome size, adapted to bees and bumblebees |
| Companilactobacillus | Companion-lactobacillus, referring to them growing in association with other lactobacilli in cereal, meat and vegetable fermentations | Type species: C. alimentarius. Homofermentative with strain- or species-specific ability to ferment pentoses, vancomycin resistant, unknown ecology, likely nomadic |
| Lapidilactobacillus | Lactobacilli from stones | Type species: L. concavus. Homofermentative with strain- or species-specific ability to ferment pentoses, vancomycin resistant, unknown ecology. |
| Agrilactobacillus | Lactobacilli from fields | Type species: A. composti. Homofermentative, aerotolerant and vancomycin resistant. Genome size, G+C content of the genome and the source of the two species suggest a free-living lifestyle of the genus. |
| Schleiferilactobacillus | Karl Heinz Schleifer's lactobacilli | Type species: S. perolens. Homofermentative, vancomycin resistant, aerotolerant. Schleiferilactobacillus spp. have a large genome size, ferment a wide range of carbohydrates, and spoil beer and dairy products by copious production of diacetyl. |
| Loigolactobacillus | spoiling lactobacilli | Type species: L. coryniformis. Homofermentative, vancomycin resistant, mesophilic or psychrotrophic organisms. |
| Lacticaseibacillus | Lactobacilli related to cheese | Type species: L. casei. Homofermentative, vancomycin resistant; many species ferment pentoses, and are resistant to oxidative stress. L. casei and related species have a nomadic lifestyle. |
| Latilactobacillus | Widespread lactobacilli | Type species: L. sakei. Homofermentative, mesophilic free living and environmental lactobacilli. Many strains are psychrotrophic and grow below 8 °C. |
| Dellaglioa | Franco Dellaglio's lactobacilli | Type species: D. algida. Homofermentative, vancomycin resistant, aerotolerant and psychrophilic. |
| Liquorilactobacillus | Lactobacilli from liquor or liquids | Type species: L. mali. Homofermentative, vancomycin resistant, motile organisms growing in liquid, plant-associated habitats. Many liquorilactobacilli produce EPS from sucrose and degrade fructans with extracellular fructanases. |
| Ligilactobacillus | Uniting lactobacilli | Type species: L. salivarius. Homofermentative, vancomycin resistant, most ligilactobacilli are host adapted and many strains are motile. Several strains of Ligilactobacillus express urease to withstand gastric acidity. |
| Lactiplantibacillus | Lactobacilli related to plants | Type species: L. plantarum. Homofermentative, vancomycin resistant organisms with a nomadic lifestyle that ferment a wide range of carbohydrates; most species metabolise phenolic acids by esterase, decarboxylase and reductase activities. L. plantarum expresses pseudocatalase and nitrate reductase activities. |
| Furfurilactobacillus | Lactobacilli from bran | Type species: F. rossiae. Heterofermentative, vancomycin resistant, with large genome size, broad metabolic potential and unknown ecology. |
| Paucilactobacillus | Lactobacilli fermenting few carbohydrates | Type species: P. vaccinostercus. Heterofermentative, vancomycin resistant, mesophilic or psychrotrophic, aerotolerant, most strains ferment pentoses but not disaccharides. |
| Limosilactobacillus | Slimy lactobacilli | Type species: L. fermentum. Heterofermentative, thermophilic, vancomycin resistant with two exceptions, Limosilactobacillus species are vertebrate host adapted and generally form exopolysaccharides from sucrose to support biofilm formation in the upper intestine of animals. |
| Fructilactobacillus | Fructose-loving lactobacilli | Type species: F. fructivorans. Heterofermentative, vancomycin resistant, mesophilic, aerotolerant, small genome size. Fructilactobacilli are adapted to narrow ecological niches that relate to insects, flowers, or both. |
| Acetilactobacillus | Lactobacilli from vinegar | Type species: A. jinshani. Heterofermentative, vancomycin resistant, grow in the pH range of 3-5; fermenting disaccharides and sugar alcohols but few hexoses and no pentoses. |
| Apilactobacillus | Lactobacilli from bees | Type species: A. kunkeei. Heterofermentative, vancomycin resistant, small genome size, fermenting only few carbohydrates, adapted to bees and/or flowers. |
| Levilactobacillus | -leavening lactobacilli | Type species: L. brevis. Heterofermentative, vancomycin resistant, mesophilic or psychrotrophic, metabolise agmatine, environmental or plant-associated lifestyle. |
| Secundilactobacillus | Second lactobacilli, growing after other organisms depleted hexoses | Type species: S. collinoides. Heterofermentative, vancomycin resistant, mesophilic or psychrotrophic, environmental or plant-associated lifestyle. Adapted to hexose-depleted habitats, most strains do not reduce fructose to mannitol but metabolize agmatine and diols. |
| Lentilactobacillus | Slow lactobacilli | Type species: L. buchneri. Heterofermentative, vancomycin resistant, mesophilic, fermenting a broad spectrum of carbohydrates. Most lentilactobacilli are environmental or plant-associated, metabolise agmatine and convert lactate and/or diols. L. senioris and L. kribbianus form an outgroup to the genus; both species were isolated from vertrebrates and may transition to a host-adapted lifestyle. |