Lactobacillus rhamnosus

Lacticaseibacillus rhamnosus (previously: Lactobacillus rhamnosus^[1]) is a bacterium that originally was considered to be a subspecies of L. casei, but genetic research found it to be a separate species in the L. casei clade, which also includes L. paracasei and L. zeae.^[2][3] It is a short Gram-positive homofermentative facultative anaerobic non-spore-forming rod that often appears in chains. Some strains of L. rhamnosus bacteria are being used as probiotics, and are particularly useful in treating infections of the female urogenital tract, most particularly very difficult to treat cases of bacterial vaginosis (or "BV").^[4] The species Lacticaseibacillus rhamnosus and Limosilactobacillus reuteri are commonly found in the healthy female genito-urinary tract and are helpful to regain control of dysbiotic bacterial overgrowth during an active infection. L. rhamnosus sometimes is used in dairy products such as fermented milk and as non-starter-lactic acid bacterium (NSLAB) in long-ripened cheese.^[5] While frequently considered a beneficial organism, L. rhamnosus may not be as beneficial to certain subsets of the population; in rare circumstances, especially those primarily involving weakened immune system or infants, it may cause endocarditis.^[6] Despite the rare infections caused by L. rhamnosus, the species is included in the list of bacterial species with qualified presumed safety (QPS) status of the European Food Safety Agency.^[7]

Genome

L. rhamnosus is considered a nomadic organism^[8] and strains have been isolated from many different environments including the vagina and the gastrointestinal tract. L. rhamnosus strains have the capacity for strain-specific gene functions that are required to adapt to a large range of environments.^[9] Its core genome contains 2,164 genes, out of 4,711 genes in total (the pan-genome).^[9] The accessory genome is overtaken by genes encoding carbohydrate transport and metabolism, extracellular polysaccharides, biosynthesis, bacteriocin production, pili production, the CRISPR-Cas system, the clustered regularly interspaced short palindromic repeat (CRISPR) loci, and more than 100 transporter functions and mobile genetic elements such as phages, plasmid genes, and transposons.^[9]

The genome of the specific strain L. rhamnosus LRB, in this case, taken from a human baby tooth, consists of a circular chromosome of 2,934,954 bp with 46.78% GC content.^[10] This genome contains 2,749 total genes with 2,672 that are total protein-coding sequences.^[10] This sample did not contain any plasmids.^[10] The most extensively studied strain, L. rhamnosus GG, a gut isolate, consists of a genome of 3,010,111 bp. Therefore, the LRB genome is shorter than GG’s genome. LRB lacks the spaCBA gene cluster of GG and is not expected to produce functional pili (6).^[10] This difference may help explain why each strain lives in a different habitat.

Lacticaseibacillus rhamnosus GG (ATCC 53103) and medical use

L. rhamnosus GG (ATCC 53103) is a strain of L. rhamnosus that was isolated in 1983 from the intestinal tract of a healthy human being; filed for a patent on 17 April 1985, by Sherwood Gorbach and Barry Goldin,^[11] the 'GG' derives from the first letters of their surnames.^[12] The patent refers to a strain of "L. acidophilus GG" with American Type Culture Collection (ATCC) accession number 53103; later reclassified as a strain of L. rhamnosus. The patent claims the L. rhamnosus GG (ATCC 53103) strain is acid- and bile-stable, has a great avidity for human intestinal mucosal cells, and produces lactic acid. Since the discovery of the L. rhamnosus GG (ATCC 53103) strain, it has been studied extensively on its various health benefits and currently L. rhamnosus GG (ATCC 53103) strain is the world's most studied probiotic bacterium with more than 800 scientific studies.

The genome sequence of Lactobacillus rhamnosus GG (ATCC 53103) has been decoded in 2009.^[13][14]

Society and culture

L. rhamnosus GR-1

L. rhamnosus GR-1 was originally found in the urethra of a healthy female and is nowadays a model strain for vaginal probiotics. A genome comparison between L. rhamnosus GG and L. rhamnosus GR-1 shows that GR-1 lacks spaCBA-encoded pili, an important adhesin in L. rhamnosus GG adhesion to the intestinal epithelial cells.^[30] In contrast, L. rhamnosus GR-1 utilises lectin-like proteins to attach to carbohydrates on the surface of the target cell. Lectin-like proteins preferentially bind to nonkeratinized stratified squamous cells which are found in the urethra and vagina. The lectin-like protein 1 purified from L. rhamnosus GR-1 is found to prevent infection by the uropathogenic E. coli UTI89 by inhibiting its adhesion to epithelial cells and by disrupting its biofilm formation.^[31] Additionally, it can increase biofilm formation in other beneficial lactobacilli that inhabit the vagina.

References

Further reading