Bacteria, lactic acid cell components

Abstract Lactic acid occurs widely in nature and is produced by many life forms from bacteria to human cells. Identified in 1780 as a component of sour milk, it has been used in food, drink, pharmacentical, cosmetics, chemical and electronic industries in different forms, such as free acid (typically 80-92% in water), salts (e.g., calcium lactate), and esters (e.g., ethyl lactate). If one calculates the amount of its derivatives back to the equivalent amount of original lactic acid, the total global market volume in 2008 is estimated at around 260,000 tons of lactic acid (calculated at 100% concentration) for traditional applications [excluding poly(lactic acid)... 

Lactic acid bacteria synthesise a range of different polysaccharides, defined by their location in the cell. Some are located intracellularly and are used as energy or carbon sources others are cell wall components and some are located outside the cell wall. The latter are called extracellular polysaccharides (EPs) and are either associated with the cell wall as a slime capsule, or secreted into the environment. Many lactic acid bacteria such as Lactobacillus delbrueckii subsp. bulgaricus, Streptococcus thermo-philus and Lactococcus lactis subsp. cremoris produce EPs. 

The lipolytic activity of propionibacteria was shown to be higher than that of lactic acid bacteria (Depuis et al., 1993). Propionibacterial lipids apparently are not only structural components of the cell, but may also have a protective role against the action of some antibiotics. In the presence of polymyxin M (Konovalova, 1970) the production of lipids and phospholipids was increased (Fig. 4.15). 

Figure 1.3. Diagram of the proteolytic systems of lactic acid bacteria, (a) Extracellular components PrtP, cell-envelope proteinase PrtM, proteinase maduration protein Opp, oligopetide permease DtpT, the ion linked trasnsporter for di-and tripeptides and Opt, the ABC transporter for peptides, (b) Intracelullar components pool of about 20-25 peptidases, including general (PepN, PepC) and specific (PepX, PepQ) peptidases, and amino acid catabolic enzymes (carboxylases, aminotransferases, etc.).

Like all microorganisms, lactic bacteria cells multiply when conditions are favorable presence of nutritional factors, absence of toxic factors, and adequate temperature. All of the principal reactions of its metabolism are directed towards the biosynthesis of cellular components nucleic acids for the transmission of genetic heritage, carbohydrates, lipids, structure proteins and of course biologically active proteins. To ensure these syntheses, the cell must first find the necessary chemical elements in the medium carbon, nitrogen and minerals—in usable forms. Since aU of these synthesis reactions are endergonic, the medium must... 

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