Growth Factors, Microbial
Growth Factors, Microbial
biologically active substances (a number of amino acids, vitamins, purine and pyrimi-dine bases, sterols) whose absence prevents the growth of microorganisms even on nutrient media containing the necessary sources of energy, carbon, and nitrogen.
Microbial growth factors exert an effect on microorganisms even when present in tiny quantities. Nonsporiferous bacteria (Pseudomonas, Mycobacterium), many mold fungi (Aspergillus, Penicillium), and other microorganisms are capable of synthesizing growth factors and have no additional need for them.
Amino acids are necessary for the biosynthesis of protein, and purine and pyrimidine bases for the formation of nucleic acids. Vitamin coenzymes are especially important among the growth factors. Thus, pyridoxine (vitamin B6) participates in the transamination and deamination of amino acids, and thiamine (vitamin B1) participates in decarboxylation. Certain species of yeasts and lactic-acid bacteria will not grow on nutrient media without biotin, thiamine, pantothenic and nicotinic acids, and pyridoxine.
It was once believed that certain pathogenic microorganisms would grow only on media containing blood or blood serum, ascitic fluid, whey, or yeast autolysate. It has been found, however, that these microorganisms can grow without such substances if the appropriate growth factors are added to the nutrient medium.
If the growth factors have a complex chemical structure, the requirements for them in different microorganisms may vary. For example, the thiamine molecule is composed of thiazole and pyridine residues. Some species need completed thiamine, others synthesize it if thiazole and pyridine are present in the medium, and others grow on a medium containing thiazole only, since they are capable of synthesizing pyridine and then thiamine; a fourth group reproduces in the presence of pyridine, synthesizing thiazole and then thiamine. So-called wild-type microorganisms that are capable of synthesizing microbial growth factors are called prototrophic. By treating these organisms with mutagens, it is possible to obtain mutants lacking in a given factor (called auxotrophic, or deficient, mutants, and used for quantitative determination of vitamins and amino acids and for breeding mutants that form increased amounts of the substance).
The capacity to synthesize microbial growth factors can determine the character of the interrelationships between organisms. For example, if a certain species of yeast will not grow because growth factors are absent in the medium, the inoculation and proliferation in the culture of a species that synthesizes the factors will lead to simultaneous growth of both species. In some insects and crustaceans there are microbial symbionts that reproduce in the intestine or in special organs and supply the host with various vitamins and amino acids. Microorganisms that inhabit the rumen and intestines of ruminants and the intestines of other animals, including man, perform the same function.
REFERENCESOdintsova, E. N. Mikrobiologicheskie melody opredeleniia vitaminov. Moscow, 1959.
Ierusalimskii, N. D. Osnovy fiziologii mikrobov. Moscow, 1963.
Rose, A. Khimicheskaia mikrobiologiia. Moscow, 1971. (Translated from English.)
A. A. IMSHENETSKII