lactobacillus lactobacillus lactobacillus is a genus of gram-positive, aerotolerant anaerobes or microaerophilic, rod-shaped, non-spore-forming bacteria. until 2020, the genus lactobacillus comprised over 260 phylogenetically, ecologically, and metabolically diverse species; a taxonomic revision of the genus assigned lactobacilli to 25 genera (see § taxonomy below). not to be confused with lactobacillales. lactobacillus lactobacillus sp. near a squamous epithelial cell scientific classification domain: bacteria phylum: bacillota class: bacilli order: lactobacillales family: lactobacillaceae genus: lactobacillusbeijerinck 1901 (approved lists 1980) type species lactobacillus delbrueckii(leichmann 1896) beijerinck 1901 (approved lists 1980) species see text lactobacillus species constitute a significant component of the human and animal microbiota at a number of body sites, such as the digestive system, and the female genital system. in women of european ancestry, lactobacillus species are normally a major part of the vaginal microbiota. lactobacillus forms biofilms in the vaginal and gut microbiota, allowing them to persist during 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 probiotic found in food such as yogurt, and it is diverse in its application to maintain human well-being, as it can help treat diarrhea, vaginal infections, and skin disorders such as eczema. metabolism lactobacilli are homofermentative, i.e. hexoses are metabolised by glycolysis to lactate as major end product, or heterofermentative, i.e. hexoses are metabolised 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 (and explained) in lactiplantibacillus plantarum (previously lactobacillus plantarum). lactobacilli generally do not require iron for growth. the lactobacillaceae are the only family of the lactic acid bacteria (lab) 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. tryptophan metabolism by human gastrointestinal microbiota () tryptophan clostridiumsporogenes lacto-bacilli tryptophanase-expressingbacteria ipa i3a indole liver brain ipa i3a indole indoxylsulfate ast-120 ahr intestinalimmunecells intestinalepithelium pxr mucosal homeostasis:↓tnf-α↑junction protein-coding mrnas l cell glp-1 t j neuroprotectant:↓activation of glial cells and astrocytes↓4-hydroxy-2-nonenal levels↓dna damage–antioxidant–inhibits β-amyloid fibril formation maintains mucosal reactivity:↑il-22 production associated with vascular disease:↑oxidative stress↑smooth muscle cell proliferation↑aortic wall thickness and calcification associated with chronic kidney disease:↑renal dysfunction–uremic toxin kidneys this diagram shows the biosynthesis of bioactive compounds (indole and certain other derivatives) from tryptophan by bacteria in the gut. indole is produced from tryptophan by bacteria that express tryptophanase. clostridium sporogenes metabolizes tryptophan into indole and subsequently 3-indolepropionic acid (ipa), a highly potent neuroprotective antioxidant that scavenges hydroxyl radicals. ipa binds to the pregnane x receptor (pxr) in intestinal cells, thereby facilitating mucosal homeostasis and barrier function. following absorption from the intestine and distribution to the brain, ipa confers a neuroprotective effect against cerebral ischemia and alzheimer's disease. lactobacillus species metabolize tryptophan into indole-3-aldehyde (i3a) which acts on the aryl hydrocarbon receptor (ahr) in intestinal immune cells, in turn increasing interleukin-22 (il-22) production. indole itself triggers the secretion of glucagon-like peptide-1 (glp-1) in intestinal l cells and acts as a ligand for ahr. indole can also be metabolized by the liver into indoxyl sulfate, a compound that is toxic in high concentrations and associated with vascular disease and renal dysfunction. ast-120 (activated charcoal), an intestinal sorbent that is taken by mouth, adsorbs indole, in turn decreasing the concentration of indoxyl sulfate in blood plasma. genomes the genomes of lactobacilli are highly variable, ranging in size from 1.2 to 4.9 mb (megabases). accordingly, the number of protein-coding genes ranges from 1,267 to about 4,758 genes (in fructilactobacillus sanfranciscensis and lentilactobacillus parakefiri, respectively). 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 (moro 1900) hansen and mocquot 1970 (approved lists 1980) "lactobacillus alvi" kim et al. 2011 lactobacillus amylolyticus bohak et al. 1999 lactobacillus amylovorus nakamura 1981 lactobacillus apis killer et al. 2014 "lactobacillus backi" bohak et al. 2006 lactobacillus bombicola praet et al. 2015 lactobacillus colini zhang et al. 2017 lactobacillus crispatus (brygoo and aladame 1953) moore and holdeman 1970 (approved lists 1980) lactobacillus delbrueckii (leichmann 1896) beijerinck 1901 (approved lists 1980) 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 ginsenosidimutans" jung et al. 2013 lactobacillus hamsteri mitsuoka and fujisawa 1988 lactobacillus helsingborgensis olofsson et al. 2014 lactobacillus helveticus (orla-jensen 1919) bergey et al. 1925 (approved lists 1980) lactobacillus hominis cousin et al. 2013 lactobacillus iners falsen et al. 1999 lactobacillus intestinalis (ex hemme 1974) fujisawa et al. 1990 lactobacillus jensenii gasser et al. 1970 (approved lists 1980) "lactobacillus jinshani" yu et al. 2020 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 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 raoultii" nicaise et al. 2018 lactobacillus rodentium killer et al. 2014 lactobacillus rogosae holdeman and moore 1974 (approved lists 1980) lactobacillus taiwanensis wang et al. 2009 "lactobacillus thermophilus" ayers and johnson 1924 "lactobacillus timonensis" afouda et al. 2017 lactobacillus ultunensis roos et al. 2005 lactobacillus xujianguonis meng et al. 2020 taxonomy the genus lactobacillus currently contains 44 species which are adapted to vertebrate hosts or to insects. in recent years, other members of the genus lactobacillus (formerly known as the leuconostoc branch of lactobacillus) have been reclassified into the genera atopobium, carnobacterium, weissella, oenococcus, and leuconostoc. the pediococcus species p. dextrinicus has been reclassified as a lapidilactobacillus dextrinicus and most lactobacilli were assigned to paralactobacillus or one of the 23 novel genera of the lactobacillaceae. two websites inform on the assignment of species to the novel genera or species (http://www.lactobacillus.uantwerpen.be/; http://www.lactobacillus.ualberta.ca/). the 23 new genera of 2020 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, 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 (food) 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. algidus. 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 (host adapted) 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 (biofilm-forming) 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 (dough)-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 (growing) 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. phylogeny the currently accepted taxonomy is based on the list of prokaryotic names with standing in nomenclature and the phylogeny is based on whole-genome sequences. lactobacillus lactobacillus gallinarum lactobacillus helveticus lactobacillus acidophilus lactobacillus ultunensis lactobacillus crispatus lactobacillus amylovorus lactobacillus kitasatonis lactobacillus kefiranofaciens lactobacillus hamsteri lactobacillus gigeriorum lactobacillus pasteurii lactobacillus kilaxensis lactobacillus intestinalis lactobacillus amylolyticus lactobacillus xujianguonis lactobacillus acetotolerans lactobacillus apis lactobacillus panisapium lactobacillus bombicola lactobacillus helsingborgensis lactobacillus melliventris lactobacillus kimbladii lactobacillus kullabergensis lactobacillus porci lactobacillus delbrueckii lactobacillus equicursoris lactobacillus psittaci lactobacillus fornicalis lactobacillus jensenii lactobacillus rodentium lactobacillus iners lactobacillus colini lactobacillus hominis lactobacillus johnsonii lactobacillus taiwanensis lactobacillus gasseri lactobacillus paragasseri outgroup holzapfelia human health vaginal tract the female genital tract is one of the principal colonisation sites for human microbiota, and there is interest in the relationship between their presence and human health, with a domination by a single species being correlated with general welfare and good outcomes in pregnancy. in around 70% of women, a lactobacillus species is dominant, although that has been found to vary between american women of european origin and those of african origin, the latter group tending to have more diverse vaginal microbiota. similar differences have also been identified in comparisons between belgian and tanzanian women. interactions with pathogens lactobacilli produce