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Lactobacillus
Lactobacillus sp. near a squamous epithelial cell
Scientific classification
Domain:	Bacteria
Phylum:	Firmicutes
Class:	Bacilli
Order:	Lactobacillales
Family:	Lactobacillaceae
Genus:	Lactobacillus Beijerinck 1901
Species and subspecies[1]
Lactobacillus acetotolerans Lactobacillus acidifarinae Lactobacillus acidipiscis Lactobacillus acidophilus Lactobacillus agilis Lactobacillus algidus Lactobacillus alimentarius Lactobacillus allii Lactobacillus alvei Lactobacillus alvi Lactobacillus amylolyticus Lactobacillus amylophilus Lactobacillus amylotrophicus Lactobacillus amylovorus Lactobacillus animalis Lactobacillus animata Lactobacillus antri Lactobacillus apinorum Lactobacillus apis Lactobacillus apodemi Lactobacillus aquaticus Lactobacillus aviarius Lactobacillus aviarius subsp. araffinosus Lactobacillus aviarius subsp. aviarius Lactobacillus backii Lactobacillus bambusae Lactobacillus bifermentans Lactobacillus bombi Lactobacillus bombicola Lactobacillus brantae Lactobacillus brevis Lactobacillus brevis subsp. coagulans Lactobacillus brevis subsp. gravesensis Lactobacillus brevisimilis Lactobacillus buchneri Lactobacillus cacaonum Lactobacillus camelliae Lactobacillus capillatus Lactobacillus casei group Lactobacillus casei Lactobacillus casei subsp. casei Lactobacillus chiayiensis Lactobacillus paracasei Lactobacillus paracasei subsp. paracasei Lactobacillus paracasei subsp. tolerans Lactobacillus zeae Lactobacillus catenefornis Lactobacillus caviae Lactobacillus cerevisiae Lactobacillus ceti Lactobacillus coleohominis Lactobacillus colini Lactobacillus collinoides Lactobacillus composti Lactobacillus concavus Lactobacillus coryniformis Lactobacillus coryniformis subsp. coryniformis Lactobacillus coryniformis subsp. torquens Lactobacillus crispatus Lactobacillus crustorum Lactobacillus curieae Lactobacillus curtus Lactobacillus curvatus Lactobacillus delbrueckii Lactobacillus delbrueckii subsp. bulgaricus Lactobacillus delbrueckii subsp. delbrueckii Lactobacillus delbrueckii subsp. indicus Lactobacillus delbrueckii subsp. jakobsenii Lactobacillus delbrueckii subsp. lactis Lactobacillus delbrueckii subsp. sunkii Lactobacillus dextrinicus Lactobacillus diolivorans Lactobacillus equi Lactobacillus equicursoris Lactobacillus equigenerosi Lactobacillus fabifermentans Lactobacillus faecis Lactobacillus faeni Lactobacillus farciminis Lactobacillus farraginis Lactobacillus fermentum Lactobacillus floricola Lactobacillus florum Lactobacillus formosensis Lactobacillus fornicalis Lactobacillus fructivorans Lactobacillus frumenti Lactobacillus fuchuensis Lactobacillus furfuricola Lactobacillus futsaii Lactobacillus gallinarum Lactobacillus gasseri Lactobacillus gastricus Lactobacillus ghanensis Lactobacillus gigeriorum Lactobacillus ginsenosidimutans Lactobacillus gorillae Lactobacillus graminis Lactobacillus guizhouensis Lactobacillus halophilus Lactobacillus hammesii Lactobacillus hamsteri Lactobacillus harbinensis Lactobacillus hayakitensis Lactobacillus heilongjiangensis Lactobacillus helsingborgensis Lactobacillus helveticus Lactobacillus helveticus subsp. jugurti Lactobacillus herbarum Lactobacillus heterohiochii Lactobacillus hilgardii Lactobacillus hokkaidonensis Lactobacillus hominis Lactobacillus homohiochii Lactobacillus hordei Lactobacillus iatae Lactobacillus iners Lactobacillus ingluviei Lactobacillus insectis Lactobacillus insicii Lactobacillus intermedius Lactobacillus intestinalis Lactobacillus iwatensis Lactobacillus ixorae Lactobacillus japonicus Lactobacillus jensenii Lactobacillus johnsonii Lactobacillus kalixensis Lactobacillus kefiranofacien Lactobacillus kefiranofaciens subsp. kefiranofaciens Lactobacillus kefiranofaciens subsp. kefirgranum Lactobacillus kefiri Lactobacillus kimbladii Lactobacillus kimchicus Lactobacillus kimchiensis Lactobacillus kisonensis Lactobacillus kitasatonis Lactobacillus koreensis Lactobacillus kosoi Lactobacillus kullabergensis Lactobacillus kunkeei Lactobacillus larvae Lactobacillus leichmannii Lactobacillus letivazi Lactobacillus lindneri Lactobacillus malefermentans Lactobacillus mali Lactobacillus manihotivorans Lactobacillus mellifer Lactobacillus mellis Lactobacillus melliventris Lactobacillus metriopterae Lactobacillus micheneri Lactobacillus mindensis Lactobacillus mixtipabuli Lactobacillus mobilis Lactobacillus modestisalitolerans Lactobacillus mucosae Lactobacillus mudanjiangensis Lactobacillus murinus Lactobacillus musae Lactobacillus nagelii Lactobacillus namurensis Lactobacillus nantensis Lactobacillus nasuensis Lactobacillus nenjiangensis Lactobacillus nodensis Lactobacillus nuruki Lactobacillus odoratitofui Lactobacillus oeni Lactobacillus oligofermentans Lactobacillus oris Lactobacillus oryzae Lactobacillus otakiensis Lactobacillus ozensis Lactobacillus panis Lactobacillus panisapium Lactobacillus pantheris Lactobacillus parabrevis Lactobacillus parabuchneri Lactobacillus paracollinoides Lactobacillus parafarraginis Lactobacillus paragasseri Lactobacillus parakefiri Lactobacillus paralimentarius Lactobacillus paraplantarum Lactobacillus pasteurii Lactobacillus paucivorans Lactobacillus pentosiphilus Lactobacillus pentosus Lactobacillus perolens Lactobacillus plajomi Lactobacillus plantarum Lactobacillus plantarum subsp. argentoratensis Lactobacillus plantarum subsp. plantarum Lactobacillus pobuzihii Lactobacillus pontis Lactobacillus porci Lactobacillus porcinae Lactobacillus psittaci Lactobacillus quenuiae Lactobacillus raoultii Lactobacillus rapi Lactobacillus rennanquilfy Lactobacillus rennini Lactobacillus reuteri Lactobacillus rhamnosus Lactobacillus rodentium Lactobacillus rogosae Lactobacillus rossiae Lactobacillus ruminis Lactobacillus saerimneri Lactobacillus sakei Lactobacillus sakei subsp. carnosus Lactobacillus sakei subsp. sakei Lactobacillus salivarius Lactobacillus sanfranciscensis Lactobacillus saniviri Lactobacillus satsumensis Lactobacillus secaliphilus Lactobacillus selangorensis Lactobacillus senioris Lactobacillus senmaizukei Lactobacillus sharpeae Lactobacillus shenzhenensis Lactobacillus sicerae Lactobacillus silagei Lactobacillus silagincola Lactobacillus siliginis Lactobacillus similis Lactobacillus songhuajiangensis Lactobacillus spicheri Lactobacillus sucicola Lactobacillus suebicus Lactobacillus sunkii Lactobacillus taiwanensis Lactobacillus terrae Lactobacillus thailandensis Lactobacillus timberlakei Lactobacillus timonensis Lactobacillus tucceti Lactobacillus ultunensis Lactobacillus uvarum Lactobacillus vaccinostercus Lactobacillus vaginalis Lactobacillus vermiforme Lactobacillus versmoldensis Lactobacillus vespulae Lactobacillus vini Lactobacillus wasatchensis Lactobacillus xiangfangensis Lactobacillus yonginensis Lactobacillus zymae

Lactobacillus is a genus of Gram-positive, facultative anaerobic or microaerophilic, rod-shaped, non-spore-forming bacteria.^[2] They are a major part of the lactic acid bacteria group (i.e., they convert sugars to lactic acid). In humans, they constitute a significant component of the microbiota at a number of body sites, such as the digestive system, urinary system, and genital system. In women of European ancestry, Lactobacillus species are normally a major part of the vaginal microbiota.^[3][4]Lactobacillus forms biofilms in the vaginal and gut microbiota, allowing them to persist during harsh environmental conditions and maintain ample populations.^[5]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.^[6]Lactobacillus is 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.^[7]

Metabolism[edit]

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Many lactobacilli operate using homofermentative metabolism (they produce only lactic acid from sugars), and some species use heterofermentative metabolism (they can produce either alcohol or lactic acid from sugars).^[8] They are aerotolerant despite the complete absence of a respiratory chain.^[9][10] This aerotolerance is manganese-dependent and has been explored (and explained) in Lactobacillus plantarum.^[9] Many species of this genus do not require iron for growth and have an extremely high hydrogen peroxide tolerance.^{[citation needed]}

Tryptophan metabolism by human gastrointestinal microbiota ( v t e ) Tryptophan Clostridium sporogenes Lacto- bacilli Tryptophanase- expressing bacteria IPA I3A Indole Liver Brain IPA I3A Indole Indoxyl sulfate AST-120 AhR Intestinal immune cells Intestinal epithelium 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.[11] Indole is produced from tryptophan by bacteria that express tryptophanase.[11]Clostridium sporogenes metabolizes tryptophan into indole and subsequently 3-indolepropionic acid (IPA),[12] a highly potent neuroprotective antioxidant that scavenges hydroxyl radicals.[11][13][14] IPA binds to the pregnane X receptor (PXR) in intestinal cells, thereby facilitating mucosal homeostasis and barrier function.[11] Following absorption from the intestine and distribution to the brain, IPA confers a neuroprotective effect against cerebral ischemia and Alzheimer’s disease.[11]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.[11] Indole itself triggers the secretion of glucagon-like peptide-1 (GLP-1) in intestinal L cells and acts as a ligand for AhR.[11] 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.[11] 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.[11]

Genomes[edit]

The genomes of Lactobacillus 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 L. sanfranciscensis and L. parakefiri, respectively).^[15][16] 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.^[17]

Lactobacillus contains a wealth of compound microsatellites in the coding region of the genome, which are imperfect and have variant motifs.^[18]

Taxonomy[edit]

The genus Lactobacillus currently contains over 180 species and encompasses a wide variety of organisms.^[19] The genus is polyphyletic, with the genus Pediococcus dividing the L. casei group, and the species L. acidophilus, L. salivarius, and L. reuteri being representatives of three distinct subclades. The genus Paralactobacillus falls within the L. salivarius group. 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. More recently, the Pediococcus species P. dextrinicus has been reclassified as a Lactobacillus species.^[20] According to metabolism, Lactobacillus species can be divided into three groups:

• Obligately homofermentative (group I) including:
  
  • 
    L. acidophilus, L. delbrueckii, L. helveticus, L. salivarius
    
  
  


• Facultatively heterofermentative (group II) including:
  
  • 
    L. casei, L. curvatus, L. plantarum, L. sakei
    
  
  


• Obligately heterofermentative (group III) including:
  
  • 
    L. brevis, L. buchneri, L. fermentum, L. reuteri
    
  
  

Human health[edit]

Vaginal tract[edit]

The female genital tract is one of the principal colonisation sites for human microbiota, and there is interest in the relationship between the composition of these bacteria 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.^[3]

Interactions with other pathogens[edit]

Lactobacillus species produce hydrogen peroxide which inhibits the growth and virulence of the fungal pathogen Candida albicans in vitro and in vivo.^[21][22] In vitro studies have also shown that Lactobacillus sp. reduce the pathogenicity of C. albicans through the production of organic acids and certain metabolites.^[23] Both the presence of metabolites, such as sodium butyrate, and the decrease in environmental pH caused by the organic acids reduce the growth of hypha in C. albicans, which reduces its pathogenicity.^[23]Lactobacillus sp. also reduce the pathogenicity of C. albicans by reducing C. albicans biofilm formation.^[23] Biofilm formation is reduced by both the competition from Lactobacillus sp., and the formation of defective biofilms which is linked to the reduced hypha growth mentioned earlier.^[23] On the other hand, following antibiotic therapy, certain Candida species can suppress the regrowth of Lactobacillus sp. at body sites where they cohabitate, such as in the gastrointestinal tract.^[21][22]

In addition to its effects on C. albicans, Lactobacillus sp. also interact with other pathogens. For example, Lactobacillus reuteri can inhibit the growth of many different bacterial species by using glycerol to produce the antimicrobial substance called reuterin.^[24] Another example is Lactobacillus salivarius, which interacts with many pathogens through the production of salivaricin B, a bacteriocin.^[25]

Probiotics[edit]

Lactobacillus species administered in combination with other probiotics benefits cases of irritable bowel syndrome (IBS), although the extent of efficacy is still uncertain.^[26] The probiotics help treat IBS by returning homeostasis when the gut microbiota experiences unusually high levels of opportunistic bacteria.^[6] In addition, Lactobacillus species can be administered as probiotics during cases of infection by the ulcer-causing bacterium Helicobacter pylori.^[27] Helicobacter pylori is linked to cancer, and antibiotic resistance impedes the success of current antibiotic-based eradication treatments.^[27] When Lactobacillus probiotics are administered along with the treatment as an adjuvant, its efficacy is substantially increased and side effects may be lessened.^[27] Also, Lactobacillus is used to help control urogenital and vaginal infections, such as bacterial vaginosis (BV). Lactobacillus produce bacteriocins to suppress pathogenic growth of certain bacteria,^[28] as well as lactic acid and H₂O₂ (hydrogen peroxide). Lactic acid lowers the vaginal pH to around 4.5 or less, hampering the survival of other bacteria, and H₂O₂ reestablishes the normal bacterial microbiota and normal vaginal pH.^[28] In children, Lactobacillus strains such as L. rhamnosus are associated with a reduction of atopic eczema, also known as dermatitis, due to anti-inflammatory cytokines secreted by this probiotic bacteria.^[6].In addition, lactobacillus with other probiotic^[29] organisms in ripen milk and yogurt progress the immunity in the mucous intestine in humans through rising the number of LgA (+)

Oral health[edit]

Dental caries

Some Lactobacillus species have been associated with cases of dental caries (cavities). Lactic acid can corrode teeth, and the Lactobacillus count in saliva has been used as a "caries test" for many years. Lactobacilli characteristically cause existing carious lesions to progress, especially those in coronal caries. The issue is, however, complex, as recent studies show probiotics can allow beneficial lactobacilli to populate sites on teeth, preventing streptococcal pathogens from taking hold and inducing dental decay. The scientific research of lactobacilli in relation to oral health is a new field and only a few studies and results have been published.^[30][31] Some studies have provided evidence of certain Lactobacilli which can be a probiotic for oral health.^[32] Some species, but not all, show evidence in defense to dental caries.^[32] Due to these studies, there have been applications of incorporating such probiotics in chewing gum and lozenges.^[32] There is also evidence of certain Lactobacilli that are beneficial in the defense of periodontal disease such as gingivitis and periodontitis.^[32]

Food production[edit]

Some Lactobacillus species are used as starter cultures in industry for controlled fermentation in the production of wine, yogurt, cheese, sauerkraut, pickles, beer, cider, kimchi, cocoa, kefir, and other fermented foods, as well as animal feeds and the bokashi soil amendment. The antibacterial and antifungal activity of Lactobacillus species rely on production of bacteriocins and low molecular weight compounds that inhibits these microorganisms.^[33][34]

Sourdough bread is made either spontaneously, by taking advantage of the bacteria naturally present in flour, or by using a "starter culture", which is a symbiotic culture of yeast and lactic acid bacteria growing in a water and flour medium. The bacteria metabolize sugars into lactic acid, which lowers the pH of their environment, creating a signature "sourness" associated with yogurt, sauerkraut, etc.

In many traditional pickling processes, vegetables are submerged in brine, and salt-tolerant Lactobacillus species feed on natural sugars found in the vegetables. The resulting mix of salt and lactic acid is a hostile environment for other microbes, such as fungi, and the vegetables are thus preserved—remaining edible for long periods.

Lactobacilli, especially L. casei and L. brevis, are some of the most common beer spoilage organisms. They are, however, essential to the production of sour beers such as Belgian lambics and American wild ales, giving the beer a distinct tart flavor.

See also[edit]

• Lactobacillus L. anticaries


• Lactic acid fermentation


• MRS agar


• Pediococcus


• Probiotics


• Proteobiotics


• Carbon monoxide-releasing molecules

References[edit]

External links[edit]

• 
  Data related to Lactobacillus at Wikispecies


• List of species of the genus Lactobacillus


• Lactobacillus at Milk the Funk Wiki


• 
  Lactobacillus at BacDive - the Bacterial Diversity Metadatabase