Energy and carbon source: autotrophic microorganisms grow in a culture medium composed of inorganic substances with carbon dioxide as carbon source and light or inorganic substances as energy source. For example, powder is added to the chemoautotrophic thiobacillus thiooxidans culture medium.
Sulfur is an energy source, and CO2 in the air is a carbon source. Heterotrophic microorganisms use organic matter as carbon source and energy source. Monosaccharides or disaccharides such as glucose, sucrose, maltose and lactose are often added to the culture medium, and some can use starch.
Application of cellulose and other polysaccharides or sugars in animal tissues. For example, beef sauce peptone medium is commonly used to cultivate bacteria, in which beef sauce is the main carbon source and energy source. (See medium formula, the same below)
Nitrogen source: autotrophic microorganisms use nitrogen-containing inorganic ammonium salts and nitrates as nitrogen nutrition, such as thiobacillus thiooxidans using (NH4)2SO4 as nitrogen source; Heterotrophic microorganisms are inorganic ammonium salts, nitrates or nitrogen-containing organic substances.
Nitrogen source. Autogenous nitrogen-fixing bacteria use N2 in the air as nitrogen nutrition, and its culture medium is called nitrogen-free culture medium, and no nitrogen source is added.
Mineral elements and growth factors: Microorganisms need major mineral elements such as phosphorus, potassium, sodium, sulfur, magnesium and calcium and trace elements such as iron and copper, so inorganic salts such as K2HPO4, KH2PO4, MgSO4, NaCl, KCl and FeSO4 are often added to the culture medium. Growth factors are mainly B vitamins that regulate microbial metabolic activities, and are often provided by yeast extracts and liver extracts. A variety of natural ingredients, such as beef sauce, wort, corn flour, bean sprout juice, etc. Contains a variety of inorganic elements and growth factors, without adding. Some microorganisms need special growth factors, such as Haemophilus need to add ⅴ (coenzyme) and ⅹ (heme) to the culture medium.
(3) Type of culture medium
According to the different sources of raw materials, culture media can be divided into synthetic culture media, semi-synthetic culture media and natural culture media.
Synthetic medium: composed of organic and inorganic substances with known chemical composition. Accurate composition and strong repeatability. However, nutrition is limited and microorganisms grow slowly. It is suitable for strain isolation, breeding, genetic analysis and bioassay. Such as Gauss medium for actinomycetes, Xia Jiaer medium for molds and various chemoautotrophic bacteria media.
Semi-synthetic medium: It consists of some natural substances and a small amount of chemicals with known composition. Comprehensive nutrition, which can effectively meet the nutritional needs of microorganisms. Widely used in the cultivation of microorganisms. For example, beef paste peptone culture medium for bacterial culture, potato glucose culture medium for mold culture, and various fermentation media prepared from natural substances such as corn flour and inorganic salts commonly used in industrial production.
Natural culture medium: made of natural organic matter with unknown or unbalanced chemical composition. The ingredients are complex, but the nutrition is rich and comprehensive. Commonly used in experimental research and production. Such as wort medium, corn flour medium, bran and sawdust used in production.
According to the physical properties of culture medium, it can be divided into liquid culture medium, solid culture medium and semi-solid culture medium.
Liquid culture medium: made of various nutrients and water, or made of natural substances (wort, bean sprout juice, etc.). ). The composition is uniform and suitable for the vegetative growth of various microorganisms. Widely used in experimental research and large-scale industrial production, it is beneficial to obtain a large number of bacteria or metabolites.
Solid culture medium: coagulant is added to liquid culture medium, or it is made of solid raw materials such as bran. The commonly used coagulant is agar (also known as agar and watercress), which is extracted and processed from seaweed such as agar. The commercially available agar is strip, flake or powder, and its main component is sulfated polygalactose, which cannot be decomposed by most microorganisms and only plays an auxiliary role in the culture medium. Its melting point is about 98℃, freezing point is 42℃, and the aqueous solution of 1.5 ~ 2% (2% ~ 2.5% recorded in books) is in a gel state at ordinary culture temperature. Agar solid culture medium is widely used in the separation, culture, strain identification and preservation of microorganisms.
Semi-solid medium: liquid medium containing 0.2 ~ 0.5% agar. Used to observe the movement of bacteria, identify strains and determine the titer of phage.
According to the use of culture medium, it can be divided into selection medium, identification medium, enrichment medium and basic medium.
Selective medium: a medium designed according to the special nutritional requirements of a certain type or microorganism to improve the separation efficiency of the required microorganisms. Such as nitrogen-free culture medium for separating nitrogen-fixing microorganisms, adding filter paper strips or cellulose powder as carbon source to separate cellulose-decomposing bacteria. Adding a compound to the culture medium can effectively isolate microorganisms resistant to this compound. For example, adding a few drops 10% phenol to actinomycetes culture medium can inhibit the growth of bacteria and molds. Adding a certain amount of penicillin and streptomycin can inhibit the growth of bacteria.
Identification medium: according to the metabolic characteristics of microorganisms, indicators are added to the medium to identify different microorganisms through color reaction. For example, eosin-methylene blue culture medium is used to check whether dairy products and drinking water are contaminated by intestinal bacteria. When intestinal bacteria such as Escherichia coli grow, lactose in the fermentation medium discolors the added eosin-methylene blue, which is purple-black and metallic when deposited on the colony.