Therefore, in the culture medium should contain all these nutrients in amounts corresponding to the specific needs of the organism. However, the physiology of microorganisms is extremely diverse, and so are as varied their specific nutritional needs. For the cultivation of microbes offered literally thousands of different media, and often in the description of these environments does not specify precisely why they put those or other components. Meanwhile, the composition of the culture medium can and must be based on scientific principles of nutrition. These principles will be discussed in this section.
Because the chemical composition of cells which is broadly identical in all living organisms, it is clear which substances must first be necessary for their growth. Approximately 80-90% of the total cell mass is water, so the water is always quantitatively is the most important nutrient. As the study supply almost all organisms needed potassium, magnesium, calcium, iron, manganese, cobalt, copper, molybdenum and zinc. The table below summarizes the known functions of these 15 elements in the cell.
All the necessary metals body can receive in the form of cations of inorganic salts. The desired amount of manganese, cobalt, copper, molybdenum, and zinc are very small; often even it is difficult to prove that these elements are really necessary, since they are present in sufficient amounts as impurities in inorganic basic media components. Therefore, they are often called microelements or trace elements. One of nonmetals, phosphorus can also be added to the medium in an inorganic form — in the form of phosphates.
It should be noted that certain groups of microorganisms are additional specific requirements for minerals. For example, diatom cell walls of algae, and some other highly saturated silicon, these organisms require silicon that is added to the medium as the silicate. Although most microorganisms can not identify the need for sodium, some marine and photosynthetic bacteria (including cyanobacteria), it requires relatively high concentrations. In these cases it can not be replaced by other monovalent cations.
Requirements for carbon, nitrogen, sulfur and oxygen can not be described as easy, as certain groups of organisms should be getting these elements to a certain chemical form.
The need for carbon-
Photosynthetic organisms, and those bacteria that derive their energy from the oxidation of inorganic compounds usually used as the sole or major carbon source of CO2 — a compound containing carbon in the most oxidized form. The conversion of CO2 into organic components of the cell — the recovery process requires energy. Accordingly, these physiological groups microorganisms significant portion of the energy received from the light or by oxidation of reduced inorganic compounds must be expended for recovery of CO2 to the level of organic matter.
All other organisms prepared essentially of carbon organic nutrient. Most organic substrates oxidized to the same level as the organic components of the cell. Therefore, in order to serve as cellular carbon sources, they do not usually require prereduction. But organic substrate is used not only for biosynthesis; they must also meet the energy needs of the cell. Therefore, a significant portion of the carbon in the organic substrate is guided along the paths of metabolism, which provide energy and eventually removed from the cell in the form of CO2 (the main product of aerobic metabolism) or a mixture of CO2 and organic compounds (the typical end-products of fermentation) . Thus, organic nutrients usually play a dual role: they serve as both a source of carbon and energy sources. Many microorganisms can fully meet their needs in carbon some one organic compound. Others, however, are unable to grow in the presence of only one organic compound, and require a variety of additional organic substances. These auxiliary substances are necessary solely for the purpose of biosynthesis and are used as precursors of certain organic components of cells that the organism can not synthesize itself completely. They are called growth factors, and the role they will be discussed in more detail below.
Microorganisms are extremely diverse in relation to how the type and number of those organic compounds which may be used as the main carbon and energy source. The variety is so great that when any native organic compound can be used by any organism. Therefore, the detailed description of the chemical nature of the organic carbon source for the microorganisms is not possible. This extraordinary diversity of needs in carbon — one of the most interesting aspects of the physiology of microbes.
In studying the needs of organic compounds in selected microorganisms it is that some of them are very «polyphagous», while others are highly specialized. For example, some bacteria of the Pseudomonas group can be used as the sole carbon and energy source for more than 90 different organic compounds (Table. Below). At the other end of the spectrum are bacteria that oxidize methane, which can use only two organic substrate — methane and methanol, as well as some bacteria capable of cleaving cellulose and using only the substrate.
Most organisms that depend on the organic carbon sources (and perhaps all), also require very small amounts of CO2, because the compound is necessary for some biosynthetic reactions. But since it is usually organisms use organic substrate to form a large amount of carbon dioxide therein need for biosynthetic purposes can be satisfied by this source.
Most photosynthetic organisms absorb these two elements in an oxidized state — in the form of inorganic salts (nitrates and sulfates). Therefore they are first recovered, and then used in the biosynthesis. Some microorganisms are unable to recover nitrogen and (or) the corresponding sulfur anions, and these elements are necessary in their reduced form. The need for reduced nitrogen spread widely enough; in these cases can be given to nitrogen in the form of ammonium salts. The need for reduced sulfur is less common; a sulfur source can serve as sulfides or any organic compounds containing sulfhydryl groups (e.g., cysteine).
The need for nitrogen and sulfur
The need for nitrogen and sulfur can often be satisfied by organic substances containing N and S in the reduced form (amino acids or more complex products of protein breakdown, such as peptones). Such compounds can often serve as sources of energy and carbon; in that case they need to immediately satisfy the cells and carbon and nitrogen, and sulfur. Some bacteria can use N2 — the most abundant source of nitrogen in nature. This process is called nitrogen fixation, and its first step consists in recovering the ammonia to N2.
Any organic compound which is needed by the body as a precursor to or part of the cells of the organic material, but that he can not be synthesized from a simple carbon sources must be provided in the diet. Such organic nutrients called growth factors. Vitamins are part of prosthetic groups or active sites of certain enzymes.
Since growth factors satisfy only the specific needs associated with the processes of biosynthesis, they are needed only in small quantities in comparison with the main source of carbon — the main precursor of organic material of the cell. The composition includes approximately 20 proteins, various amino acids, so that the need for any single amino acid, which the cells can not synthesize itself is not too large. This applies also to the need for any purine or pyrimidine, since the nucleic acid consists of five different compounds of this type. Vitamins are needed in even smaller quantities, as various coenzymes for which they serve as precursors, act as a catalyst because of their content in the cell is measured in millions of shares of the dry matter of the cell.
The biosynthesis of amino acids, purines, pyrimidines and coenzymes usually involves complex chains of individual reactions. If the body is unable to carry out at least one of these reactions, it must obtain it from the outside in the final product as a growth factor. However, the body needs is not always a factor in finished form. If blocked by one of the early steps in the biosynthesis of the chain, the particular needs of the cell can be satisfied by organic precursors, which are formed in the circuit after the blocked portion. A detailed analysis of the needs of different microorganisms in any factor usually indicates that they need in different chemical forms of this factor. Some microorganisms as a growth factor, it is imperative the whole molecule. However, there are organisms that can be given to the two halves of the molecule separately: they are able to join them. Other micro-organisms need only pyrimidine moiety as part of the thiazole can synthesize their own. Finally, there are those who need a thiazole moiety because they can synthesize pyrimidine portion and connects it to the thiazole. These groups of organisms differ in the minimum growth factor requirements, but in any case, the cell should, eventually, to have the whole molecule thiamine; thiamine therefore can be given as a growth factor microorganisms of any type described above. However, even the whole molecule of thiamine — it is not a compound that the body uses itself as a necessary component of the cell. Thus functioning in the cell material is kokarboksilaza coenzyme that participates as a prosthetic group in several enzymatic reactions.