Lactic acid bacteria mechanisms

A component of the ribotide reductase complex of enzymes, protein Ba, has been shown to contain two non-heme iron atoms per mole (77). This enzyme plays a vital, albeit indirect, role in the synthesis of DNA. Curiously, the lactic acid bacteria do not employ iron for the reduction of the 2 hydroxyl group of ribonucleotides. In these organisms this role has been assumed by the cobalt-containing vitamin Bi2 coenzyme (18). The mechanism of the reaction has been studied and has been shown to procede with retention of configuration (19). 

The key feature which draws attention to these peptides in respect to food applications is their ability to inhibit undesirable organisms, either spoilage or pathogenic organisms. Although the peptides from eukaryotic sources appear far-removed from immediate application in foods, it is important to study their mechanism(s) of action in relation to those of lactic acid bacteria to better understand commonalities in structure-function Such commonalities may serve as a base from which to initiate molecular... 

The mechanism(s) by which lactic acid bacteria inhibit or inactivate other bacteria is not totally clear. Daly et al. (1972), Speck (1972), and Gilliland and Speck (1972) have cited evidence which suggests that the following may be involved (1) production of antibiotics such as nisin, diplococcin, acidophilin, lactocidin, lactolin, and perhaps others (2) production of hydrogen peroxide by some lactic acid bacteria (3) depletion of nutrients by lactic acid bacteria, which makes growth of pathogens difficult or impossible (4) production of volatile acids (5) production of acid and reduction in pH (6) production of D-leucine and (7) lowering the oxidation-reduction potential of the substrate. 

The mechanisms by which probiotics (and prebiotics) produce beneficial effects on the gut have not yet been fully elucidated. However, at least three mechanisms of action have been proposed (i) antibacterial agents produced by probiotic organisms may have an inhibitory effect on pathogenic microbes (ii) immune responses may be enhanced to suppress potential pathogens and (iii) competition in the gut epithelium may allow lactic acid bacteria and bifidobacteria to supplant pathogenic organisms. 

The approach of Casiot et al. [21] was soon accepted and followed in the held of Se speciation. Wrobel et al. [91] applied a bacterium (Arthrobacter luteus) derived lysing enzyme mixture added with PMSF to study the intermediary molecules of Se metabolism of Se-enriched yeast without proteolysis. In order to tailor the cell wall degrading mechanism to the samples under test, Michalke et al. [77] used bacterial lisozyme and pronase E, either alone or in combination, for the Se speciation of Se-enriched lactic acid bacteria. Independent and simultaneous experiments were carried out with the two enzymes, thus achieving outstanding total Se-extraction efficiency (85-105 percent) with the sole application of pronase E and relatively low chromatographic recovery (8-12 percent) (still... 

Grbin et al. 2007). ATHP reduction may lead to EHTP. As ethanol is a precursor, mousy off-flavour occurs after alcoholic fermentation, preferably after lactic acid bacteria activity. It seems that the formation of mousiness may be induced by oxidation but it is not clear if the effect is on the microorganisms or in any chemical reaction stimulated by the redox potential. Other agents claimed to affect its production (high pH, low sulphite, residual sugar content) (Lay 2004 Snowdon et al. 2006 Romano et al. 2007) are also stimulators of microbial activity and so the true mechanisms are not yet clarified, but the non-enzymatic chemical synthesis has been ruled out in D. anomala (Grbin et al. 2007). 

Both in eukaryotic cells and in lactic acid bacteria, the mechanisms involves pyruvate being reduced to lactate. The enzyme catalyzing this reaction is lactate dehydrogenase. The equilibrium for this reaction lies far in favor of formation of lactate. 

Phage infection is still the principal problem faced by cheese makers. Mechanisms by which lactic acid bacteria resist phage infection are known and work is in progress to engineer strains with superior phage resistance. 

Can lactic acid bacteria (LAB) exopolysaccharides (EPSs) play a role in improving gastrointestinal health More specifically, can the EPSs serve another role by interacting with the human immune system or even the human microbiome itself More recent gains in knowledge of the mechanisms by which EPS interacts with the intestinal tract, the microbiome and immune function seem to present an additional nutritional role that is offered by fermented dairy products. 

Foerst, R, Reitmaier, J., Kulozik, U. (2006). Importance of drying matrix and mechanism of protection of probiotic lactic acid bacteria during vacuum drying. 

Biodegradation of mycotoxins has become an area of great interest. Biological detoxification involves the enzymatic degradation or transformation of toxins to less toxic componnds and is often a detoxification or resistance mechanism nsed by microbes or plants for protection from adverse impacts of toxins. It has been shown that S. cerevisiae and lactic acid bacteria are potential candidates for mycotoxin decontamination (Halady Shetty Jespersen, 2006). 

Simpson, W. J., Fernandez, J. L. (1994). Mechanism of resistance of lactic acid bacteria to frawi -isohumulone. Journal of the American Society of Brewing Chemists, 52, 9-11. 

Study of the mechanism of the oxidation of pyruvic acid by certain bacteria led to the discovery of lipoic acid (thioctic acid) as a nutrient metabolite essential for the oxidative decarboxylation of a-keto acids. It subsequently was determined that the acetate-replacing factor " for lactic acid bacteria and protogen,a growth factor for the protozoan, Tetrahymena gelii, were also identical with lipoic acid. The occurrence of considerable quantities of lipoic acid in mammalian preparations of pyruvate and a-ketoglutarate oxidases suggests that it has the same function in animal tissues as in microorganisms. ... 

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