Лактобактериялар тәртібі және олардың маңызы

Order of bacteria

Lactobacillales are an order of gram positive, low GC, acid tolerant, generally nonsporulating, nonrespiring, either rod shaped (bacilli) or spherical (cocci) bacteria that share common metabolic and physiological characteristics. These bacteria, usually found in decomposing plants and milk products, produce lactic acid as the major metabolic end product of carbohydrate fermentation, giving them the common name lactic acid bacteria (LAB). Production of lactic acid has linked LAB with food fermentations, as acidification inhibits the growth of spoilage agents. Proteinaceous bacteriocins are produced by several LAB strains and provide an additional hurdle for spoilage and pathogenic microorganisms. Furthermore, lactic acid and other metabolic products contribute to the organoleptic and textural profile of a food item. The industrial importance of the LAB is further evidenced by their generally recognized as safe (GRAS) status, due to their ubiquitous appearance in food and their contribution to the healthy microbiota of animal and human mucosal surfaces. The genera that comprise the LAB are at its core Lactobacillus, Leuconostoc, Pediococcus, Lactococcus, and Streptococcus, as well as the more peripheral Aerococcus, Carnobacterium, Enterococcus, Oenococcus, Sporolactobacillus, Tetragenococcus, Vagococcus, and Weissella. All but Sporolactobacillus are members of the Lactobacillales order, and all are members of the Bacillota phylum. Although lactic acid bacteria are generally associated with the order Lactobacillales, bacteria of the genus Bifidobacterium (phylum Actinomycetota) also produce lactic acid as the major product of carbohydrate metabolism.

The lactic acid bacteria (LAB) are either rod shaped (bacilli), or spherical (cocci), and are characterized by an increased tolerance to acidity (low pH range). This aspect helps LAB to outcompete other bacteria in a natural fermentation, as they can withstand the increased acidity from organic acid production (e. g., lactic acid). Laboratory media used for LAB typically include a carbohydrate source, as most species are incapable of respiration. LAB are catalase negative. LAB are amongst the most important groups of microorganisms used in the food industry. Their relative simple metabolism has also prompted their use as microbial cell factories for the production of several commodities for the food and non food sectors

In 1985, members of the diverse genus Streptococcus were reclassified into Lactococcus, Enterococcus, Vagococcus, and Streptococcus based on biochemical characteristics, as well as molecular features. Formerly, streptococci were segregated primarily based on serology, which has proven to correlate well with the current taxonomic definitions. Lactococci (formerly Lancefield group N streptococci) are used extensively as fermentation starters in dairy production, with humans estimated to consume 1018 lactococci annually. Partly due to their industrial relevance, both L. lactis subspecies (L. l. lactis and L. l. cremoris) are widely used as generic LAB models for research. L. lactis ssp. cremoris, used in the production of hard cheeses, is represented by the laboratory strains LM0230 and MG1363. In similar manner, L. lactis ssp. lactis is employed in soft cheese fermentations, with the workhorse strain IL1403 ubiquitous in LAB research laboratories. In 2001, Bolotin et al. sequenced the genome of IL1403, which coincided with a significant shift of resources to understanding LAB genomics and related applications.

Probiotics are products aimed at delivering living, potentially beneficial, bacterial cells to the gut ecosystem of humans and other animals, whereas prebiotics are indigestible carbohydrates delivered in food to the large bowel to provide fermentable substrates for selected bacteria. Most strains used as probiotics belong to the genus Lactobacillus. (Other probiotic strains used belong to the genus Bifidobacterium). Probiotics have been evaluated in research studies in animals and humans with respect to antibiotic associated diarrhea, travellers' diarrhea, pediatric diarrhea, inflammatory bowel disease, irritable bowel syndrome and Alzheimer's disease. Future applications of probiotics have been conjectured to include delivery systems for vaccines and immunoglobulins, and the treatment of different gastrointestinal diseases and vaginosis. Some LAB produce bacteriocins which limit pathogens by interfering with cell wall synthesis or causing pore formation in the cell membrane. Nisin, a bacteriocin produced by LAB, was first researched as a food preservative in 1951 and has since been widely commercially used in foods due to its antimicrobial activity against Gram positive bacteria. Nisin is utilized as a food additive in at least 50 countries. Furthermore, LAB have the potential to reduce the abundance of mycotoxins in foods by binding to them.

Researchers have studied the impact of lactic acid bacteria on indoleacetic acid production, phosphate solubilization, and nitrogen fixation on citrus. While most of the bacterial isolates, were able to produce IAA, phosphate solubilization was limited to only one of the eight LAB isolates.

Lactic acid bacteria are used in the food industry for a variety of reasons such as the production of cheese and yogurt products. Popular drinks such as kombucha are made using lactic acid bacteria, with kombucha having been known to have traces of Lactobacillus and Pediococcus once the drink is made. The beer and wine making process utilizes certain lactic acid bacteria, mostly Lactobacillus. Lactic acid bacteria is used to start the wine making process by starting the malolactic fermentation. After the malolactic fermentation, yeast cells are used to start the alcoholic fermentation process in grapes. The malolactic fermentation mechanism is mainly transformation of L malic acid (dicarboxylic acid) to an lactic acid (monocarboxylic acid). This change occurs due to the presence of malolactic and malic enzymes. All malic acid are degraded and this increase the pH levels which changes the taste of the wine. By using molecular biology, researchers can help pick out different desirable strains that help improve the quality of wine and help with the removable of the undesirable strains. The same can be said about brewing beer as well which uses yeast with some breweries using lactic acid bacteria to change the taste of their beer.

A broad number of food products, commodity chemicals, and biotechnology products are manufactured industrially by large scale bacterial fermentation of various organic substrates. Because this involves cultivating enormous quantities of bacteria each day in large fermentation vats, a serious threat in these industries is the risk of contamination by bacteriophages, which can rapidly bring fermentations to a halt and cause economical setbacks. Areas of interest in managing this risk include the sources of phage contamination, measures to control their propagation and dissemination, and biotechnological defense strategies developed to restrain them. In the context of the food fermentation industry, the relationship between bacteriophages and their bacterial hosts is very important. The dairy fermentation industry has openly acknowledged the problem of phage contamination, and has worked for decades with academia and starter culture manufacturers to develop defence strategies and systems to curtail phages' propagation and evolution.

The first contact between an infecting phage and its bacterial host is the phage's attaching to the host cell. This attachment is mediated by the phage's receptor binding protein (RBP), which recognizes and binds to a receptor on the bacterial surface. RBPs are also referred to as host specificity proteins, host determinants, and antireceptors. A variety of molecules have been suggested to act as host receptors for bacteriophages infecting LAB; among those are polysaccharides and (lipo)teichoic acids, as well as a single membrane protein. A number of RBPs of LAB phages have been identified by the generation of hybrid phages with altered host ranges. These studies, however, also found additional phage proteins to be important for successful phage infection. Analysis of the crystal structure of several RBPs indicates that these proteins share a common tertiary folding, and support previous indications of the saccharide nature of the host receptor. Gram positive LAB have a thick peptidoglycan layer, which must be traversed to inject the phage genome into the bacterial cytoplasm. Peptidoglycan degrading enzymes are expected to facilitate this penetration, and such enzymes have been found as structural elements of a number of LAB phages. Dextrans, like other glucan, enable bacteria to adhere to the surface of teeth, which in turn can cause tooth decay through the formation of dental plaque and production of lactic acid. While the primary bacteria responsible for tooth decay is Streptococcus mutans, LAB do feature among the other most common oral bacteria that cause decay.