Lactobacillus johnsoniiRANK: Species
TAXONOMY: Terrabacteria group -> Firmicutes -> Bacilli -> Lactobacillales -> Lactobacillaceae -> Lactobacillus -> Lactobacillus johnsonii
Identified as a constituent of the oral microbiome by Human Oral Microbiome Database. Lactobacillus johnsonii is one of the many microorganisms that reside in the human intestine. Like all species of the Lactobacillus genus, it is an anaerobic, Gram-positive bacterium, which has a rod-like shape and does not undergo spore formation (1). The human gastrointestinal tract in which L. johnsonii resides is abundant with nutrients and relies upon more than 500 microbial species that inhabit it in order to develop and function properly. Specifically L. johnsonii and other GI tract microbes aid in polysaccharide and protein digestion and also generate a variety of nutrients, including vitamins and short-chain fatty acids that make up 15% of a human’s total caloric intake. In addition, because L. johnsonii is able to undergo fermentation and can therefore make lactic acid, it plays a major role in the fermentation and preservation of various food items, such as dairy, meat, vegetable products, and cereal. Finally, L. johnsonii is characterized as being part of the “acidophilus complex” of the Lactobacillus genus. This complex is comprised of six Lactobacillus species that are thought to be involved in probiotic activities, meaning they are able to undergo processes that are thought to be beneficial to human general health and well-being. Such probiotic benefits particularly attributed to L. johnsonii include immunomodulation, pathogen inhibition, and epithelial cell attachment .
Lactobacillus johnsonii is known to increase the number of Paneth cells, which are a host cell type that produces antimicrobial compounds, and are located together with stem cells in the intestinal crypt. Due to its metabolic limitations and reliance on exogenous sources of nutrients, L. johnsonii is typically found in human and animal gastrointestinal tract where it can obtain nutrients from its host. As an auxotrophic bacterium that lacks certain enzymes needed for the digestion of complex carbohydrates, it is unable to compete with other GI tract bacteria such as Bifidobacteria, which inhabit the colon. Therefore L. johnsonii resides in the upper GI tract, which is rich in amino acids and peptides. Specifically, it is one of the dominant microorganisms found at the junction between the ileum of the small intestine and the cecum of the colon . Other species within the Lactobacillus genus can be found in food, vegetation, sewage, and various areas of the human body. In humans, Lactobacillus species can be found in the intestine, oral cavity, and the vagina. L. johnsonii, in particular, has many genes and transporters that allow it to release bile salt hydrolase, an important enzyme that is characteristic of microorganisms that live in the GI tract. Since L. johnsonii devotes many genes for the encoding of bile salt hydrolase, its importance and ability to compete and survive in its ecosystem can be correlated with its ability to produce such large amounts of this essential enzyme.
In addition, lactic acid bacteria, such as L. johnsonii are able to produce bacteriocins which have antibacterial properties that lactic acid bacteria can use against other microorganisms, thus providing them with ways to survive in their ecosystem. For example, L. johnsonii is able to produce Lactacin F, a bacteriocin which can kill other Lactobacillus species as well as Enterococcus species in the GI tract. Thus, this microbe is thought to use this bacteriocin as a way to compete in the microbe-rich environment in which it lives. Some lactic acid bacteria have been shown to use quorum sensing as a regulator for the expression of genes involved in the production of bacteriocins. For example, some species of the Lactobacillus genus such as Lactobacillus sake have been shown to utilize quorum sensing as a means of regulating bacteriocin gene expression .
This species has been identified as a resident in the human gastrointestinal tract based on the phylogenetic framework of its small subunit ribosomal RNA gene sequences.[PMC 4262072]