User:YamsLeap/Lacticaseibacillus casei

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Lacticaseibacillus casei is an organism that belongs to the the largest genus in the family Lactobacillaceae, a lactic acid bacteria (LAB), that was previously classified as Lactobacillus casei-01. This bacteria has been identified as facultatively anaerobic or microaerophilic, acid-tolerant, non-spore-forming bacteria. The taxonomy of this group has been debated for several years because researchers struggled to differentiate between the strains of L. casei and L. paracasei. It has recently been accepted as a single species with five subspecies: L. casei subsp. rhamnosus, L. casei subsp. alactosus, L. casei subsp. casei,  L. casei subsp. tolerans, and L. casei subsp. pseudoplantarum . The taxonomy of this genus was determined according to the phenotypic, physiological, and biochemical similarities.

This species is a non-sporing, rod-shaped, gram positive microorganism that can be found within the reproductive and digestive tract of the human body. Since L. casei can survive in a variety of environmental habitats, it has and continues to be extensively studied by health scientist. Commercially, L. casei is used in fermenting dairy products and its application as a probiotic. This particular species of Lacticaseibacillus is documented to have a wide pH and temperature range, and complements the growth of L. acidophilus, a producer of the enzymeamylase (a carbohydrate-digesting enzyme).

Dairy
The most common application of L. casei is industrial, specifically for dairy production to enhance their flavor and texture. Lacticaseibacillus casei, when fermenting sugars, produces lactic acid that is crucial for fermenting dairy product. The optimum pH for this species is 5.5, but the production of lactic acid cause the pH level of its environment to decrease.

This is typically the dominant species of nonstarter lactic acid bacteria (i.e. contaminant bacteria) present in ripening cheddar cheese, and, recently, the complete genome sequence of L. casei ATCC 334 has become available. L. casei is also the dominant species in naturally fermented Sicilian green olives.

Commercial probiotic
Among the best-documented, probiotic L.casei, L. casei DN-114001, and L. casei Shirota have been extensively studied and are widely available as functional foods (see Actimel, Yakult). L. casei is a facultative heterofermentative LAB that ferments to lactic acid. Due to this, it withstands highly acidic environments which is crucial for its role as a probiotic.

Probiotics must tolerate acid stress as it travels through the gastrointestinal tract. L. casei uses the Arginine deimindase pathway, an energy dependent catabolic system used to derive ATP, ornithine, CO2 and NH3 from arginine, to lower the pH level of it's environment. In addition, the acidic environment causes the levels of glucose-phosphotransferase system (PTS) and the proteins found on the surface of the bacteria to increase to help it survive.

Another commercially available form of L. casei can be found in Danactive made by Dannon. They registered trademarked L. casei as L. casei Immunita.

Characteristics of Lactobacillus casei
The following table includes the colony, morphological, physiological, and biochemical characteristics of L. casei. I added a new section to the article (Characteristics of L. casei) that includes several biochemical test results and information about the taxonomy to the introduction paragraph. These changes were done and added to Lacticaseibacillus casei article on 04/21/22.

Transformation
Lactic acid bacteria (LAB) is widely exploited for its probiotic and fermenting properties, so understanding how its genetic material is exchanged was crucial for researchers. A wide variety of comparative analyses were used to determine that horizontal gene transfer (HGT) influenced the evolution of the Lactobacillus genus. HGT in L. casei includes transformation, conjugation, and transduction. The mobile genetic elements found within the genome, known as mobilomes, play an important role in Lactobacillaceae transfer. This includes insertion sequences, bacteriophages, integrons, plasmids, genomic islands, and transposons. Within LAB, they are responsible for metabolizing different molecules, hydrolyzing proteins, resisting antibiotics, DNA and phages, and modifying genetic elements.

The first form of gene transfer is transformation. This includes the uptake of naked extracellular DNA by a recipient bacterial cell to gain the genetic information of a donor cell. This occurs after a donor bacterium has undergone autolysis and its DNA fragments are left within the free extracellular fluid. The recipient bacterium will then ingest the DNA fragments and will result in either a bacterial cell with a plasmid or recombination of the recipient DNA will transpire within the chromosome.

The next form of transfer is conjugation, a process that involves the transfer of DNA from a donor to a recipient via cell-to-cell contact or direct cytoplasmic contact. In this process, the recipient cell is known as the transconjugant. Once the cells come together, fragments of DNA are directly transferred from the donor to the transconjugant. This is mediated by pheromone-induced cell aggregation and mobilization proteins since many of the plasmids are unable to transfer on their own. Afterward, the mating bacterial cells will separate and a recombinant cell will be produced after homologous recombination.

Finally, transduction is the bacteriophage-mediated transfer of plasmid or chromosomal genetic information. To initiate this process, a bacteriophage must first infect the donor cell so that lysis of the cell will occur. At this point, the cell lysate is filled with phages that carry donated genome fragments and the recipient cell will be injected with abnormal phage. This will result in a recombination cell whether the cell is infected after homologous recombination or after the infection occurs by bacteriophage integrase.

A subheading was added to Characteristics of L. casei to describe horizontal gene transfer of LAB.