On the carbon source and nitrogen source in the culture medium

The medium is also the basis for the growth and reproduction of microorganisms. Among them, the carbon source and nitrogen source, like the two wheels of a car and the wings of a bird, play a crucial role in the growth and development of microorganisms.

Carbon source is the source of carbon in the structural materials and metabolites of microbial cells. It has many functions, one is to provide energy for microorganisms to maintain life activities; the other is as the basic raw material of cells, participating in the construction of various structural components of cells, such as cell walls, cell membranes, nucleic acids, etc. Carbon is present. Common carbon sources are quite rich in types. Sugars, such as glucose, can be called high-quality carbon sources that are easily used by microorganisms. Most microorganisms flock to them and can quickly ingest and metabolize them to obtain the energy and substances needed for growth. In addition, starch is also a common carbon source. Although its structure is more complex than that of glucose, it can be converted into easily absorbed sugars after hydrolysis by amylase secreted by microorganisms, which can be used by microorganisms. Other microorganisms can use fats, organic acids, etc. as carbon sources because microorganisms have diverse metabolic pathways to adapt to the supply of carbon sources in different environments.

Nitrogen sources are also indispensable for microorganisms. They are important raw materials for microorganisms to synthesize nitrogen-containing biological macromolecules such as proteins and nucleic acids. Proteins are the executors of life activities and participate in key processes such as catalysis and material transportation of various metabolic reactions in cells; nucleic acids carry genetic information and are related to the inheritance and variation of microorganisms. Among inorganic nitrogen sources, ammonium salts and nitrates are quite common. Ammonium ions in ammonium salts can be directly absorbed and utilized by microorganisms to participate in the synthesis of amino acids and proteins. Nitrates need microorganisms to reduce them to ammonium ions through specific metabolic pathways before they can be used. Organic nitrogen sources such as peptone and beef paste are rich in a variety of amino acids, polypeptides and other ingredients, which can provide microorganisms with more comprehensive nitrogen sources and other growth factors to promote the growth of microorganisms. Different microorganisms have different requirements for nitrogen sources. Some microorganisms prefer inorganic nitrogen sources because their metabolic pathways can efficiently utilize such simple nitrogen sources; while others prefer organic nitrogen sources to meet their complex nutritional requirements. The ratio of carbon and nitrogen sources in the

medium is also crucial. An appropriate carbon-nitrogen ratio can ensure the normal growth and metabolism of microorganisms. If the carbon-nitrogen ratio is unbalanced, it may cause microbial growth to be poor, or the synthesis of metabolites will be inhibited. For example, if there are too many carbon sources and insufficient nitrogen sources, although microorganisms can consume a large amount of carbon sources for energy, due to the lack of nitrogen sources, it is difficult to synthesize enough protein and nucleic acid, resulting in their growth stagnating before the logarithmic stage and unable to achieve the ideal growth density. On the contrary, if there are too many nitrogen sources and relatively insufficient carbon sources, microorganisms may use too much energy for nitrogen metabolism, and the energy used for cell construction and proliferation is reduced, which is not conducive to the normal growth of microorganisms.

In summary, in-depth exploration of the characteristics, functions and appropriate ratios of carbon and nitrogen sources in the culture medium is of great significance for optimizing microbial culture conditions, improving microbial fermentation efficiency, and even promoting the development of biotechnology-related fields.