Microbial genetics is based on virusBacteria, small fungi, unicellular animals and plantsgeneticsBranch disciplines.Microorganisms have the characteristics of small genetic individuals, short life cycle, rapid reproduction on simple synthetic medium, and can handle a large number of individuals under the same conditions, so they are good materials for genetic research.The development of microbial genetics in the 1940s and 1950s promoted the clarification of some basic theories in genetics;In the 1950s and 1960smolecular geneticsDevelopment of.
Molecular genetics is a branch of genetics developed on the basis of microbial genetics.Genetic code, transcription, translation, messenger ribonucleic acid (mRNA), transfer ribonucleic acid (tRNA), etc. are all found or confirmed in microorganisms.
Microbial genetics promotes the development of production.The principle of improving the final product by eliminating repression has been applied to the fermentation production of amino acids and nucleotides and has achieved significant yield increase.The application prospect of recombinant DNA technology in industry, agriculture and medicine is more difficult to estimate, and recombinant DNA technology is also the product of microbial genetics research.Microbial genetics research has also made important contributions to medical and health undertakings, especially in the detection of carcinogens.
Microbial genetics is a branch of genetics that focuses on viruses, bacteria, small fungi, single-cell animals and plants and other microorganisms.Microorganisms have the characteristics of small individuals, short life cycle, rapid reproduction on simple synthetic medium, and can treat a large number of individuals under the same conditions, so they are good materials for genetic research.
Development History
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Microbial Genetics
In the mid-1930s, genetic research on yeast, neurospora and paramecium began, but at that time, the research objects were limited to microorganisms capable of sexual reproduction, and the research topics were mostly limited to gene separation, linkage and recombination.American geneticist GW. Biddle and biochemist E50. Tatum.They originally attempted to clarify the original function of genes through the research on the inheritance of compound eye pigment of Drosophila melanogaster. Although some progress has been made, it is not ideal. So they used Neurospora as the research material to study the role of genes in the biosynthesis of amino acids.The reasons for this are: ① The molecular structure and biosynthetic pathway of Drosophila compound eye pigment are complex, and it is difficult to obtain a large number of pigments; ②The molecular structure or biosynthesis of amino acids is simpler than that of pigments; ③Neurospora is easy to obtain its metabolites through mass culture; ④Just as the mutant that cannot synthesize pigment must be obtained in the study of compound eye pigment of Drosophila melanogaster, the mutant that cannot synthesize amino acid must be obtained in order to study the role of genes in amino acid synthesis.To achieve this, the studied organism must be able to synthesize all amino acids by itself. Neurospora is such a organism; ⑤The research on gene isolation, linkage and recombination of Neurospora has a certain foundation; ⑥It has been reported that gene mutation is induced by irradiation in microorganisms.[1]
fundamental research
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Auxotrophic type
Microbial Genetics
In the early 1940s, Bedell and Tatum obtained a variety of auxotrophs by treating neurospora with radiation. These mutants can only grow by adding substances that they cannot synthesize in the culture medium.The important significance of studying nutritional deficiency type is: ① providing an effective means for the study of biosynthetic metabolic pathway; ②The hypothesis of one gene and one enzyme is proposed; ③The principle of exploring metabolic pathways by nutritional deficiency has been widely used in various fields of genetics; ④In addition to studying the original function of genes, it is also used to study gene structure and gene mutation. Many principles obtained from these studies are later applied to the genetic research of human somatic cells (see somatic cytogenetics), thus promoting the development of human genetics; ⑤Using nutritional deficiencies as markers, bacterial conjugation was found.
Gene recombination
As early as the 1930s, someone raised the question of whether bacteria have gene recombination, and tried to verify it. However, because the morphology of genetic recombination and sugar fermentation traits used to detect genetic recombination were not very stable, and the method of selecting recombination bodies by excluding parents was not used, no credible results were obtained.In 1946, American microbial geneticists J. Ledberg and Tatum discovered the phenomenon of bacterial gene recombination in E. coli by using the trophic deficiency type as a selective marker.This discovery not only shows the universality of genetic laws in biological world;It has also opened up a wide field of genetic research using Escherichia coli and other materials.Escherichia coli has been the most thoroughly studied organism in genetics. Through the genetic research of Escherichia coli and its phages, molecular genetics has been created.The discovery of Escherichia coli gene recombination also led to the discovery of E. coli transduction, fungal quasi sexual reproduction and actinomycetes gene recombination, and opened up prospects for the application of microbial genetics theory to production practice.
chemical analysis
The transformation of Pneumococcus pneumoniae was discovered in 1928, but the chemical nature of the transformation factor was not recognized by the American chemist OT. Avery identified it as DNA.After that, the significance of DNA was gradually recognized, and the development of molecular genetics was possible.
Drug mutation
Microbial Genetics Books
Whether bacterial resistance comes from gene mutation or adaptive variation to the environment is a long-term controversial issue.In 1943, S. Luria, a former doctor, and M. Delbruk, a geneticist who turned from physics to bacteriophage genetics, used wave experiments to prove that drug resistance can occur before bacteria contact drugs, indicating that drug resistance is the result of gene mutation.There have been many reports on bacterial variation since the 19th century, but it is from this experiment that we came to a clear conclusion about the essence of variation through rigorous experimental design and result analysis.This work has a profound impact on microbial genetics in terms of methodology, and its conclusions have deepened people's understanding of the universality of biological variation laws.
Genetic research
The research in this field has been carried out systematically by Del Bruck in the late 1930s, and entered its heyday in the 1940s.More than 90% of the dry weight of bacteriophage is composed of protein and nucleic acid. When bacteriophage infects bacteria, only nucleic acid enters the bacterial cell, and the protein shell remains outside the cell. Hundreds of bacteriophages are released just 20 to 30 minutes after infection.Such a simple system is very conducive to the study of the nature of genetic material.It is the genetic research of bacteriophages that provides important evidence that DNA is the genetic material and triplet is the basic unit of genetic code, and clarifies that gene is an indivisible functional unit rather than a unit of mutation and recombination (see complementation). In addition, hot spots of gene mutation were found in the research of bacteriophages, which later revealed the phenomenon of gene overlap.At the same time, phage genetics is also one of the experimental bases for the concept of gene regulation.
research method
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In addition to general microbiological research methods, the most prominent methods in microbial genetic research are the screening of mutants and the application of selective culture methods.Mutants, on the one hand, can be used as markers of chromosomes, on the other hand, can be used to analyze the genetic control of various life activities.For the latter purpose, a specific type of mutant must be obtained.In higher animals and plants, although there are some examples of screening specific types of mutants, most of them are accumulated for a long time due to accidental occurrence.Microbial genetics research is different. Generally, work begins with screening specific mutants, such as those that cannot synthesize a certain amino acid (nutritional deficiency type), those that are resistant to a certain drug or phage, those that cannot replicate DNA at high temperatures, and those that have genetic barriers during transformationMutants that are defective in a specific enzyme and that lead to changes in a functional area of a protein.The rapid development of microbial genetics is closely related to the availability of needed mutants.
The success of screening specific mutants is mainly due to the application of selective media.For example, when a large number of bacteria sensitive to a certain drug are inoculated on the medium containing the drug, the bacteria that can form colonies on it are the bacteria with drug resistance mutations.This principle is also applied to the study of mutation, bacterial conjugation, transduction, gene fine structure analysis (see gene localization) and gene regulation.The application of selective culture method has greatly improved the work efficiency. In the analysis of gene recombination, it is generally necessary to determine the ratio of parent combination and recombination type in the hybrid offspring;The closer the two genes are, the more offspring of the recombination type need to be analyzed.The distance between two mutation sites in the same gene must be closer, so it is difficult to find recombination between them in higher animals and plants.The recombination between two mutation sites that are very close to each other can be detected by using selective culture method in microorganisms, because specific selection conditions can eliminate most non recombinant individuals, and only a limited number of recombinant individuals can survive.For example, the rapid lysogenic mutant r Ⅱ of Escherichia coli T4 phage can infect the host bacterium Escherichia coli B and form plaque, but it cannot form plaque on Escherichia coli K.Using Escherichia coli K as the selective culture condition, we can detect the wild type phage that appears after recombination between two very close r Ⅱ mutation sites.Due to the application of selective culture methods, it is possible to detect a large number of such mutants in a relatively short time, which not only improves the work efficiency, but also fundamentally changes the understanding of genes.
Discipline relationship
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The molecular mechanism of flagellar antigen phase transformation in Salmonella was revealed by genetic methods;The pathogenic factors of some pathogenic bacteria were analyzed.
On the one hand, the research of microbial genetics depends on the knowledge and methods of biochemistry, and on the other hand, it also makes many contributions to biochemistry.Microbial genetic methods are commonly used.
Molecular genetics is a branch of genetics developed on the basis of microbial genetics.Genetic code, transcription, translation, messenger ribonucleic acid (mRNA), transfer ribonucleic acid (tRNA), etc. are all found or confirmed in microorganisms.
Because human can not be used as experimental material, the research of human genetics is very slow.Since the 1960s: ① colony growth of cultured cells in vitro; ②Application of synthetic medium; ③Establishment of mutant cell line; ④Cell fusion.
Microbial genetics also promotes the development of production.In the 1940s, microbial breeding was limited to mutation treatment.It is particularly prominent in the detection of carcinogens (see toxicology genetics).
significance
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Some biological characteristics of some microorganisms are of great significance to the study of special problems in genetics.For example, the tetrad produced by a meiosis in ascomycetes is distributed in one ascomycete, which is helpful to the study of gene transformation.
Microbial genetics has not only promoted people's understanding of genetic laws, but also promoted their understanding of microbial metabolism, growth and development, immune mechanism and pathogenicity.For example, through the study of nutrient deficiency and sugar fermentation deficiency, the synthetic pathway of amino acids, nucleotides and other substances of some microorganisms and the metabolic mechanism of some sugars were clarified;The mechanism of bacterial spore formation was studied by using mutants that could not form mature spores;The molecular mechanism of flagellar antigen phase transformation in Salmonella was revealed by genetic methods;The pathogenic factors of some pathogenic bacteria were analyzed.
On the one hand, the research of microbial genetics depends on the knowledge and methods of biochemistry, and on the other hand, it also makes many contributions to biochemistry.The research on the biosynthesis of amino acids, nucleotides, proteins, nucleic acids and other macromolecules mostly uses microorganisms as materials, and commonly uses microbial genetic methods.
Molecular genetics is a branch of genetics developed on the basis of microbial genetics.Genetic code, transcription, translation, messenger RNA, transfer RNA, etc. are all found or confirmed in microorganisms.
Because human can not be used as experimental material, the research of human genetics is very slow.Since the 1960s, the rapid development of human genetics is mainly due to the application of microbial genetics research methods to human cells in vitro.Its main links are: colony growth of cultured cells in vitro;Application of synthetic medium;Establishment of mutant cell lines;Cell fusion.They are also applicable to the genetic research of higher animals and plants, and becomeSomatic cytogeneticsImportant research methods.
Microbial genetics also promotes the development of production.In the 1940s, microbial breeding was limited to mutation treatment.With the development of microbial genetics, hybridization, transduction and transformation technologies have also been applied to breeding.After the mechanism of gene regulation in bacterial amino acid anabolism was clarified, the principle of improving the final product by eliminating repression was applied to the fermentation production of amino acids and nucleotides, and significant yield increase was achieved.
The application prospect of recombinant DNA technology in industry, agriculture and medicine is more difficult to estimate, and recombinant DNA technology is also the product of microbial genetics research.Microbial genetics research has also made important contributions to medical and health undertakings, especially in the detection of carcinogens.
