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Microbiological synthesis is an industrial process for the preparation of chemical compounds and products (eg feed yeast), implemented through the vital activity of the microbial cells. Sometimes the industrial processes based on the use of immobilized cells are a;lso referred to the microbiological synthesis.
Some products of microbiological synthesis, such as baker's yeast, have long been used by a man, but the widespread use of microbiological synthesis began in 40-50th of the 20th century in connection with the development of the penicillin production. The appearance of new sectors of the economy - the microbiological industry – refers also to this time.
In microbiological synthesis the complex substances are formed from simpler ones as a result of the functioning of the enzyme systems of a microbial cell. By this it is different from the fermentation, as a result of which the various products of microorganisms metabolism are formed (alcohols, organic acids, etc.), but preferably as a result of the enzymatic decomposition of organic substances.
Microbiological synthesis uses the ability of certain organisms to propagate itself at a high speed (there are bacteria and yeasts the biomass of which increases in 500 times faster than that of the most productive crops) and the ability of "supersynthesis" – the excessive formation of metabolic products (amino acids, vitamins, etc) that exceeds the requirements of microbial cells.
For microbiological synthesis of organic compounds the cheapest source of nitrogen are used as raw materials (e.g., nitrates and ammonium salts) and carbon (e.g., carbohydrates, organic acids, alcohols, fats, hydrocarbons including gaseous). Microbiological synthesis involves the number of successive stages. The main of them are the preparation of the necessary culture of the microorganism - producer, the producer cultivation, the cultivation of the producer in the given conditions, in the course of which the microbiological synthesis is carried out (this stage is often called fermentation), filtration and separation of biomass, isolation and purification of the desired product (if necessary), drying.
The fermentation is carried out in special reactors (fermenters), equipped with devices for mixing the medium and sterile air supply. Process control may be effected electronically. It is most convenient to carry out the fermentation in a continuous manner - with a constant supply of nutrient medium and yield of products of microbiological synthesis. In such a way, for example, feed yeast are produces. However, the majority of metabolites are produced by a batch process – with the yield of the product at the end of the process.
The most important products of microbiological synthesis:
Antibiotics. Most antibiotics accumulate themselves outside the cells of the microorganism-producer, which are mostly actinomyces, some fungi and bacteria (mainly mutant forms). Antibiotics applied mainly in medicine are highly purified. Antibiotics for the treatment of farm animals have a specific activity relative to the most common diseases such as helminthiasis, coccidiosis and others. Typically or the feed additive the medium concentrate is produced after cultivation of the producer in it, sometimes together with the biomass that contains the substantial amounts of other metabolic products including vitamins, amino acids and nucleotides etc.
Amino acids. The significant advantage of the microbiological synthesis of the amino acids is the possibility of their receiving as natural isomers (L-form). The producers of amino acids are mainly mutants lacking a number of enzyme systems, due to it the supersynthesis od the desired product is carried out. Usually the bacteria belonging to the genus Brevibacterium are used. The largest share among the amino acids produced by the global industry take lysine and glutamic acid. The mutants of microorganisms capable to supersynthesis of all encoded amino acids are received.
Nucleosidphosphats. The development of microbiological synthesis of nucleotides (inosinic, guanyl and other acids) is connected to the potential production of artificial food where they are used as flavorings. When administered in the composition of the medium for the cultivation of microorganisms of metabolic precursors of the synthesis products almost all known nucleosidphosphats including ATP can be obtained. The accumulation of nucleosidphosphats occurs mainly out of the cells of microorganisms.
Vitamins, pro-vitamins, coenzymes. By the methods of microbiological synthesis mainly vitamin B12 and its coenzyme form is produced. The producers in this process are the propionic acid bacteria. For the receiving of feed concentrates containing vitamin B12, on wastes of fermentation industry (distillery, acetone-butyl stillage and others) methaneforming bacteria complex is used. The methods of producing of vitamin B2, P-carotene and yeast enriched with ergosterol are developed. At the use of appropriate metabolic precursors the microbiological synthesis of nicotinamide coenzymes such as nicotinamide adenine dinucleotide is possible.
Alkaloids. Fungi of the ergot genus (Claviceps) are the produsers of ergot alkaloids in the basis of the molecular structure of which is heterocycle ergoline. Some of these alkaloids (eg., ergometrine and ergotamine) are used as masterbatches. The numerous producers of other alkaloids are also described..
Gibberellins. Their microbiological synthesis is performed by culturing of the fungi belonging to the class of the As-comycetes, e.g. Gibberella fujikuroi. Gibberellins are isolated from the filtrate of the culture broth. Chemically they are tegracyclic carboxylic acids relating to diterpenes.
Enzymes. The producers of enzymes are numerous representatives of microscopic fungi, some actinomycetes and other bacteria. The technology for producing enzyme preparations is simplified if the enzyme is produced in the culture medium. When you select the intracellular enzymes it is necessary first to destroy the cells of microorganisms. For research and analytical purposes and etc. usually the enzymes are received prepared as a homogeneous (individual) proteins. At industrial processing of agricultural raw materials in the food industry sometimes the complex enzyme preparations are used. Thus, when processing raw plant materials the enzyme complex should contain a cellulases, hemicellulases, pectinases, proteases and some other enzymes. One of the most important enzymes produced by microbiological synthesis is glucoisomerase that catalyzes the isomerisation of glucose to fructose. The formed glucose-fructose syrup is used in the food industry instead of sucrose.
Protein-vitamin preparations. Microbial biomass as a source of protein attracts the particular attention. Production of such biomass on the cheap raw materials is considered as one of the means to eliminate the growing shortage of protein in animal feed. The industrial methods of microbiological synthesis of feed yeast got most intensive development, they are used in the form of dry biomass as a source of protein and vitamins in animal husbandry.
Some plant protection products such as bacterial entomopathogenic preparations that cause the death of harmful insects and prevent their mass reproduction also refer to the products of microbiological synthesis.
A special case of microbiological synthesis is the microbiological transformation of organic compounds. It is carried out due to the high activity of specific enzyme systems of microorganisms which catalyze the conversion of material without changing its basic structure. The most studied is the transformation of steroid compounds, such as their dehydrogenation, deacetylation and hydroxylation in well-defined positions. Thanks to the broad possibility of selection of microorganisms (the carriers of specific enzyme systems) the method of microbiological transformation is becoming more common.