Microbiology is one of the branches of biology. It studies the morphological structure, growth and reproduction of various microorganisms (bacteria, actinomycetes, fungi, viruses, rickettsia, mycoplasma, chlamydia, spirochete protozoa and single-cell algae) at the molecular, cellular or population level. , physiological metabolism, genetic variation, ecological distribution and classification evolution and other basic laws of life activities, and apply them to science in fields such as industrial fermentation, medicine and health, and bioengineering.
Discipline Impact
Microbiology is an important basic course or professional basic course that must be taught in biology majors in colleges and universities. It is also the theoretical and technical foundation of modern high-tech biotechnology. Genetic engineering, cell engineering, enzyme engineering and fermentation engineering were formed and developed based on the principles and technologies of microbiology; "Microbiology" is also one of the important cornerstones for the development of biological majors in higher agricultural and forestry colleges and the modernization of agriculture and forestry. With the widespread application of biotechnology, microbiology will have a huge impact on modern and future human production activities and life.
2. More absorption, faster conversion 1. Small volume, large specific surface area The size is measured in um, but the specific surface area (surface area/volume) is large, (insert table), there must be a huge nutrient absorption, Metabolic waste excretion and environmental information receiving surface. This characteristic is also the key to distinguishing microorganisms from all large organisms. For example: Lactobacillus: 120,000; Egg: 1.5; Human (200 pounds): 0.3 2. Large absorption and fast transformation. This characteristic provides a sufficient material basis for rapid growth and reproduction and the production of large amounts of metabolites. For example: 3 grams of gophers consume as much food as their body weight every day; 1 gram of green hummingbirds consume twice their body weight in food every day; E. coli consumes 2,000 times their body weight in sugar per hour; bacteria fermenting lactose within an hour It can decompose lactose that is 1,000 to 10,000 times its own weight to produce lactic acid; 1 kilogram of yeast can ferment thousands of kilograms of sugar in one day to produce alcohol; 3. Growth and reproduction are extremely high. For example, E.coli divides once every 20-30 minutes. If it divides continuously, the number of bacteria will increase to 2.2×1043 in 48 hours, nutrient consumption, metabolic accumulation, and growth rate will be limited. This feature can convert a large amount of substrates into useful products in a short period of time, shortening the scientific research cycle. There are also downsides, such as disease and food mold. For example: Escherichiacoli (E. coli) can divide once every 12.5 to 20 minutes under optimal growth conditions; in liquid culture media, the concentration of bacterial cells is generally 108 to 109 cells/ml; Brevibacterium glutamicum : Shake flask seeds → 50-ton fermentation tank: The number of cells can increase 3.2 billion times in 52 hours. By utilizing this characteristic of microorganisms, short-cycle, high-efficiency production in the fermentation industry can be achieved. For example, when producing fresh yeast, it can be harvested almost every 12 hours, hundreds of times a year. The following table shows the generation time and daily proliferation rate of several microorganisms. Microorganism name generation time, number of divisions per day, temperature, daily proliferation rate
Lactic acid bacteria 38 minutes 38 25 2.7×1011
Escherichia coli 18 minutes 80 37 1.2×1024
Rhizobia 110 points 13 25 8.2×103
Bacillus subtilis 31 points 46 30 7.0×1013
Photosynthetic bacteria 144 points 10 30 1.0×103
Saccharomyces cerevisiae 120 minutes 12 30 4.1×103
Chlorella 7 hours 3.4 25 10.6
Nostida* 23 hours 1.04 25 2.1 < /p>
Diatom 17 hours 1.4 20 2.64
Paramecium 10.4 hours 2.3 26 4.92
* is the old name of Candida (Nostoc), which belongs to the same prokaryotic family as bacteria biology. 4. Strong adaptability and easy mutation. Extremely flexible and adaptable, with amazing adaptability to extreme environments, and genetic material is easy to mutate. What's more important is that microorganisms have many types of physiological metabolism and many types of metabolites.
For example: Microorganisms are found in sedimentary rocks 10,000 meters deep, 85 kilometers high, and 128 meters and 427 meters below the ground. Number of species of microorganisms, according to 1972: Lower limit of type, higher limit of tendency species
Viruses and Rickettsia 1217 1217 1217
Mycoplasma 42 42 42
< p>Bacteria and Actinomycetes>1000 1500 1500Cyanobacteria 1227 1500 1500
Algae 15051 23100 23100
Fungi 37175 47300 68939
< p>Protozoa 24068 24068 30000Total number 79780 98727 127298
5. Wide distribution, many species, wide distribution area and wide distribution environment. There are many types of physiological metabolism, and many types and numbers of metabolites. What is more important is the physiological metabolism of microorganisms. There are many types of penicillins and many types of metabolites. Microorganisms can be found in any environment where other organisms exist, and they can also be found in extreme environments where other organisms cannot survive. For example: The yield of the penicillin-producing bacterium Penicillium chrysogenum (Penicillium chrysogenum) was 20 units of penicillin per ml of fermentation broth in 1943. Over the past 40 years, through the unremitting efforts of microbial genetic breeders around the world, the yield variation of this strain has gradually accumulated. Coupled with improvements in fermentation conditions, the current fermentation level in advanced countries in the world has exceeded 50,000 units per milliliter, or even close to 100,000 units. Quantitative trait variation and breeding of microorganisms can increase yields to such a large extent that it is absolutely impossible to achieve in animal and plant breeding. Because of this, almost all microbial fermentation factories attach great importance to strain selection. Microbial effects: 1. Role in material circulation in nature 2. Air and water purification, sewage treatment 3. Industrial and agricultural production: bacteria, metabolites, metabolic activities 4. Contribution to life sciences
Edited version Section classification and naming
The taxonomic units of microorganisms: kingdom, phylum, class, order, family, genus, and species are the most basic taxonomic units. Each taxonomic unit can be followed by subphylum, subclass, and subclass. Order, subfamily... Taking brewer's yeast as an example, its taxonomic status is: Kingdom: Phyllum: Fungi (Class): Ascomycota (Order): Endospores Family: Endosporaceae Genus: Saccharomyces Species: Saccharomyces yeast Species: It is a basic taxonomic unit; it is a large group of highly similar phenotypic characteristics and extremely close genetic relationships. A general term for strains that are significantly different from other species in the same genus. ① Strain refers to any purebred group produced by an independent isolated single cell and all its descendants (a group of purebred descendants that originate from the same ancestor and maintain the characteristics of the ancestor). Therefore, pure cultures from different sources of a microorganism can be called a strain of that species. Strains emphasize genetically pure lineages. For example: two strains of Escherichia coli: EscherichiacoliB and EscherichiacoliK12. Representation of strains: If species is the basic unit of taxonomy, then strain is actually the basic unit of application, because different strains of the same species are used in production. There will be great differences and differences in the types of enzymes or metabolite production! ② Subspecies or variety: subclassification within a species. When different strains within a certain species have a small number of obvious and stable variation characteristics or genetic shapes that are not enough to distinguish them into new species, these strains can be subdivided into two or more small taxa - subspecies. kind. Variant is a synonym for subspecies. Since the word "variant" can easily cause confusion in the meaning of the word, the word variant is no longer used after 1976. The mutant strains obtained in the laboratory are usually called subspecies.
For example: E.colik12 (wild type) does not require special aa, but after laboratory mutation, a defective type of a certain aa can be obtained from k12, which is called a subspecies of E.colik12. ③Type (form): often refers to subdivisions below subspecies. When the character differences between different strains of the same species or the same subspecies are not enough to be classified into new subspecies, they can be subdivided into different types. For example: they are divided into different serotypes based on differences in antigenic characteristics. Naming of microorganisms: There are two types of names for microorganisms: common names and scientific names. Such as: red bread mold - Neurospora crassa; Pseudomonas aeruginosa - Pseudomonas aeruginosa. Scientific name - is the scientific name of a microorganism, which is named according to the rules developed by the International Committee on the Classification of Microorganisms. Scientific names are composed of Latin words or Latinized loanwords. There are two types of scientific naming: the binomial method and the trinomial method. ① Binary nomenclature: scientific name = genus name + species name + (first named celebrity) + currently named celebrity + year of naming Genus name: Latin noun or adjective used as a noun, singular, with the first letter capitalized, indicating the main characteristics of the microorganism , constructed by microorganisms, shaped or named by scientists. Species name: Latin adjective with lowercase initials. It is the secondary characteristics of the microorganism, such as the microorganism's pigment, shape, origin or scientist's name, etc. Examples: Escherichiacoli (Migula) CastellanietChalmers1919 Staphylococcus aureusStaphylococcusaureusRosenbach1884 When referring to a certain genus of microorganisms in general, but not specifically to a certain species (or unspecified species name) in the genus, sp can be added after the genus name. .or ssp. (representing the singular and plural forms of the species abbreviation respectively). For example: Saccharomycessp. represents a species in the genus Saccharomyces. Strain name: Add numbers, place names or symbols after the species name. For example: BacillussubtilisAS1.389AS=AcademiaSinica BacillussubtilisBF7658BF=Beifang ClostridiumacetobutylicumATCC824 Clostridium acetobutylicum
Definition of microorganisms
Modern definition: Microorganisms are the general term for all tiny organisms that are invisible or unclear to the naked eye. Organisms that are small in size and simple in structure and can usually be seen clearly using optical microscopes and electron microscopes are collectively called microorganisms. (But some microorganisms can be seen, such as fungi, mushrooms, Ganoderma lucidum, etc.)
Features
The individuals are tiny, generally <0.1mm. The structure is simple, including unicellular, simple multicellular, and non-cellular. They have a low evolutionary status and mostly rely on organic matter to sustain life.
Classification
Prokaryotes: Tribacteria, Trisomy. Trisomy: bacteria, cyanobacteria, actinomycetes Trisomy: mycoplasma, chlamydia, rickettsia Eukaryote: fungi, protozoa, microscopic algae. Non-cellular: viruses, subviruses (viroids, mimetics, prions).
Five major characteristics:
Small size, large area; Absorption of many microorganisms, rapid transformation
; Strong growth, rapid reproduction; Strong adaptability, easy to Variation; wide distribution and many types.
Edit this group of taxa
Category Prokaryotes: bacteria, actinomycetes, spirochetes, mycoplasma, rickettsiae, and chlamydia. Eukaryotes: fungi
, algae, protozoa. Non-cellular: viruses and subviruses. Generally, in textbooks in mainland China, microorganisms are divided into the following eight categories: bacteria, viruses, fungi, actinomycetes, rickettsiae, mycoplasma, chlamydia, and spirochetes.
Bacteria
(1) Definition: A type of prokaryotes with short and thin cells, simple structure, tough cell wall, multiplication by binary fission and strong aquaticity (2) Distribution : Warm, humid and organic-rich places (3) Structure: Mainly single-celled prokaryotes, with spherical, rod, and spiral shapes. Basic structure: cell membrane, cell wall, cytoplasm, nucleoplasm. Special structures: capsule, flagella, pili, Spore (4) Reproduction: Mainly reproduce by binary fission (5) Colony: A single bacterium is invisible to the naked eye. When a single or a small number of bacteria multiply in large numbers on a solid medium, a colony visible to the naked eye will be formed. A daughter cell community with a certain morphological structure. Bacteria are an important basis for identification of bacterial species. Different types of bacterial colonies have different sizes, shapes, glossiness, colors, hardness, and transparency.
Actinobacteria
< p> (1) Definition: A type of highly terrestrial prokaryotes that mainly grow in mycelial shapes and reproduce by spores(2) Distribution: those with lower water content and richer organic matter, In slightly alkaline soil (3) Morphological structure: mainly composed of hyphae, including basal hyphae and aerial hyphae (some aerial hyphae can mature and differentiate into spore filaments to produce spores) (4) Reproduction: through Asexual reproduction is carried out by forming asexual spores. Asexual reproduction is asexual reproduction. Sexual reproduction (5) Colony: on solid culture medium: dry, opaque, dense velvet-like surface, colored dry powder
Virus
< p> (1) Definition: A type of "non-cellular organism" composed of a few components such as nucleic acids and proteins, but its survival must depend on living cells. (2) Structure: [font class="Apple-style- span" style="font-family: -webkit-monospace; font-size: 13px; line-height: normal; white-space: pre-wrap; "]Protein capsid and nucleic acid (nucleic acid is DNA or RNA)[/ font] (3) Size: The general diameter is about 100nm, the largest virus diameter is 200nm vaccinia virus, and the smallest virus diameter is 28nm poliovirus (4) Proliferation: A significant feature of the life activities of viruses is parasitism. sex. Viruses can only live within certain types of living cells. And use the environment and raw materials in the host cell to quickly replicate and increase value. In the non-parasitic state, it is crystalline and cannot carry out independent metabolic activities. Take phage as an example: adsorption → DNA injection → replication, synthesis → assembly → release of phage to infect bacteria. Schematic diagram of the processEdit the characteristics of microorganisms in this section
Chemical composition of microorganisms
C, H, O, N, P, S and other elements
Nutrition materials for microorganisms
1 Water and inorganic salts 2 Carbon source: whatever can provide microorganisms Nutrient source of carbon required for growth and reproduction 3 Nitrogen source: any nutrient source that can provide the necessary nitrogen for microorganisms Function: mainly used for the synthesis of proteins, nucleic acids and nitrogen-containing metabolites 4 Energy: can provide microbial life Activities provide nutrients or radiant energy as the initial source of energy
Classified according to carbon sources and energy
5 growth factors: trace organic matter indispensable for the growth of microorganisms
Energy Microorganisms that cause disease in humans and animals are called pathogenic microorganisms, and they fall into eight categories: 1. Fungi: cause skin diseases. Infection in deep tissues. 2 Actinomycetes: skin and wound infections. 3 spirochetes: skin diseases, blood infections such as syphilis, leptospirosis. 4 Bacteria: skin diseases, suppuration, upper respiratory tract infections, urinary tract infections, food poisoning, sepsis, acute infectious diseases, etc. 5 Rickettsia: typhus, etc. 6 Chlamydia: trachoma, genitourinary tract infection. 7 viruses: hepatitis, Japanese encephalitis, measles, AIDS, etc. 8 Mycoplasma: pneumonia, urinary tract infection. There are tens of thousands of species of microorganisms in the biological world, most of which are beneficial to humans, while only a few can cause disease.
Some microorganisms that are not usually pathogenic but can cause infection under certain circumstances are called opportunistic pathogens. They can cause food deterioration and corruption. It is precisely because they decompose natural objects that they can complete the material cycle of nature.
The role of microorganisms
Edit the contribution of this paragraph
Several basic and important discoveries and theories of modern biology were made in the process of studying microorganisms or in the process of studying microorganisms. Microorganisms are obtained as experimental materials and tools. These theories include: proving that DNA (deoxyribonucleic acid) is the carrier of genetic information (three classic experiments: pneumococcus transformation experiment, phage experiment, and plant virus recombination experiment). The semi-conservative replication method of DNA (each sub-strand of the double helix is ??a replication template). Interpretation of genetic codons (64 codons each correspond to 20 amino acids and which termination signal). Transcriptional regulation of genes (the concepts and regulation methods of operon, promoter, operator, repressor, and activator). Translation regulator of messenger RNA (terminator) etc…. Nowadays, many common and general biological research techniques rely on microorganisms, such as molecular cloning and expression of recombinant proteins in bacteria or yeast. Many medical technologies also rely on microorganisms, such as gene therapy using viruses as vectors.
Edit this paragraph: The status of microorganisms in the entire living world
Before humans discovered and studied microorganisms, they divided all living things into two distinct kingdoms - the animal kingdom and the plant kingdom. . As people's understanding of microorganisms gradually deepened, the two-kingdom system experienced three-kingdom system, four-kingdom system, five-kingdom system and even six-kingdom system. It was not until the late 1970s that Americans Woese and others discovered the third life on earth. Form-archaea led to the birth of the three-domain theory of life. This theory holds that life is composed of Archaea, Bacteria and Eukarya. In the diagram "Phylogenetic Tree of Organisms", the yellow branch on the left is the Bacteria domain; the brown and purple branches in the middle are the Archaea domain; and the green branch on the right is the Eukaryotic domain. The Archaeal domain includes Crenarchaeota, Euryarchaeota and Korarchaeota; the Bacterial domain includes bacteria, actinomycetes, cyanobacteria and various other species other than Archaea. Prokaryotes; the eukaryotic domain includes fungi, protists, animals, and plants. Except for animals and plants, most other living things belong to the category of microorganisms. It can be seen that microorganisms occupy a particularly important position in the classification of biological kingdoms. The evolution of life has always been a hot topic of concern. Based on the "Cenancestor" evolutionary tree of life constructed by Brown et al. based on paralogous genes, they believe that the common ancestor of life, Cenancestor, was a protist. During the evolution process, protists produced two branches, one is prokaryotes (bacteria and archaea), and the other is proto-eukaryotes. In the subsequent evolutionary process, bacteria and archaea first evolved in different directions, and then proto-eukaryotes Eukaryotes are created when an organism eats an archaea and replaces the host's RNA genome with the archaea's DNA. From an evolutionary perspective, microorganisms are the ancestors of all living things. If we compare the age of the earth to one year, microorganisms were born around March 20, and humans appeared on the earth around 7 pm on December 31.
Review
One of the most important impacts of microorganisms on humans is the prevalence of infectious diseases. 50% of human diseases are caused by viruses. Data released by the World Health Organization show that the morbidity and mortality rate of infectious diseases rank first among all diseases. Microorganisms cause human diseases. The history of microorganisms is the history of mankind's constant struggle against them. Humanity has made great progress in the prevention and treatment of diseases, but new and reappearing microbial infections continue to occur, and a large number of viral diseases still lack effective treatments. The causative mechanisms of some diseases are unclear. The abuse of a large number of broad-spectrum antibiotics has caused strong selection pressure, causing many strains to mutate, leading to the development of drug resistance and posing new threats to human health. Some segmented viruses can mutate through recombination or reassortment. The most typical example is influenza virus.
In each influenza pandemic, influenza viruses mutate from the strains that caused previous infections. This rapid mutation creates great obstacles to vaccine design and treatment. The emergence of drug-resistant Mycobacterium tuberculosis has caused the tuberculosis infection that had been nearly controlled to become rampant around the world. Microorganisms come in all shapes and forms, and some are putrefactive, which means they cause undesirable changes in the odor and tissue structure of food. Of course some microorganisms are beneficial and are used in the production of cheese, bread, pickles, beer and wine. Microorganisms are so small that they must be seen through a microscope at approximately 1,000 times magnification. For example, for medium-sized bacteria, 1,000 of them stacked together would only be as big as a period. Think of a drop of milk. There are about 50 million bacteria per milliliter of spoiled milk, or about 5 billion bacteria per quart of milk. That is, a drop of milk can contain 5 billion bacteria. Microorganisms can cause diseases and cause mold and rot in food, cloth, leather, etc., but microorganisms also have a beneficial side. It was Fleming who first discovered penicillin from the ability of Penicillium to inhibit the growth of other bacteria. This was an epoch-making discovery for the medical field. Later, a large number of antibiotics were screened out from the metabolites of actinomycetes and other bacteria. The use of antibiotics saved countless lives during World War II. Some microorganisms are widely used in industrial fermentation to produce ethanol, food and various enzyme preparations; some microorganisms can degrade plastics, treat wastewater and gas, etc., and have great potential for renewable resources, and are called environmentally friendly microorganisms; and some can Microorganisms that survive in extreme environments, such as high temperature, low temperature, high salt, high alkali, high radiation, and other environments where ordinary life cannot survive, some microorganisms still exist, etc. It seems that we have discovered a lot of microorganisms, but in fact, due to limitations of cultivation methods and other technical means, the microorganisms discovered by humans today only account for a small part of the microorganisms that exist in nature. Because microorganisms are small and have simple structures, people fully understood them and developed them into a discipline. Compared with other disciplines, it is still very late. Despite this, microorganisms are already widely used. The working people of our country have recognized the existence and role of microorganisms very early, and we are also one of the first few countries to apply microorganisms. According to archaeological speculation, winemaking with Quzhi appeared in my country 8,000 years ago. Winemaking was very common in my country more than 4,000 years ago, and the Egyptians had also learned to bake bread and brew fruit wine at that time. 2,500 years ago, the Chinese people invented brewing sauce and vinegar, and knew how to use koji to treat digestive tract diseases. In the 6th century AD (Northern Wei Dynasty), my country's Jia Sixie's masterpiece "Qi Min Yao Shu" recorded in detail the techniques of making koji, wine, sauce and vinegar. In agriculture, although nitrogen fixation by rhizobia is not yet known, legume rotations are already being used to improve soil fertility. These facts show that although people are not aware of the existence of microorganisms, they are already dealing with them. While using beneficial microorganisms, they also prevent and treat harmful microorganisms. To prevent food from spoiling, methods such as salting, candiing, drying, and acidification are used. Variolus was used to prevent smallpox during the Longqing period of our country. The use of variola to prevent smallpox is my country's major contribution to world medicine. This method has been spread to Russia, Japan, North Korea, Turkey and the United Kingdom. In 1798, the British doctor Jenner proposed using cowpox to prevent smallpox. Microbiology as a subject began with the introduction of microscopes. The development of microbiology has gone through three periods: the morphological period, the physiological period and the development of modern microbiology. The morphological observation of microorganisms in the morphological period began with the invention of the microscope by Antony Van Leeuwenhock (1632-1732). He was the first person to truly see and describe microorganisms. His microscope was considered It is the most exquisite and excellent single microscope. He used a microscope with a magnification of 50 to 300 times to clearly see bacteria and protozoa. He also reported the observation results to the Royal Society of England, with detailed descriptions and accompanying illustrations. There are accurate illustrations. In 1695, Anton Leeuwenhoek compiled a large number of his accumulated results in the book "The Secrets of Nature Discovered by Anton Leeuwenhoek". His discoveries and descriptions revealed for the first time a new biological world - the world of microorganisms. This is of epoch-making significance in the history of the development of microbiology.
Physiological period
For example, there are a large number of bacteria in the intestines of healthy people, called normal flora, which contains hundreds of bacterial species.
These bacteria are interdependent and mutually beneficial in the intestinal environment. The role of microbiota in the decomposition and absorption of food, toxic substances, and even drugs, and the interactions between bacteria are still unclear. Once the bacterial flora is imbalanced, diarrhea will occur. As medical research enters the molecular level, people are becoming increasingly familiar with professional terms such as genes and genetic materials. People realize that it is genetic information that determines the life characteristics of an organism, including its external shape and life activities, and the genome of an organism is the carrier of this genetic information. Therefore, elucidating the genetic information carried by the genome of an organism will greatly help reveal the origin and mystery of life. Studying the variation patterns, virulence and pathogenicity of microbial pathogens at the molecular level is a revolution for traditional microbiology. Microbial genome research, represented by the Human Genome Project, has become the forefront of life science research, and microbial genome research is an important branch of it. The world's authoritative magazine "Science" once rated microbial genome research as one of the world's major scientific advances. Revealing the genetic mechanism of microorganisms through genomic research, discovering important functional genes and developing vaccines based on this, and developing new antiviral, antibacterial and fungal drugs will effectively control the epidemic of new and old infectious diseases and promote the advancement of medical and health care. Rapid development and growth! Genome research on microorganisms at the molecular level provides new clues and ideas for exploring the mysteries of interactions between individual microorganisms and groups. In order to fully develop microbial (especially bacterial) resources, the United States launched the Microbial Genome Project (MGP) in 1994. By studying complete genome information to develop and utilize important functional genes of microorganisms, we can not only deepen our understanding of the pathogenic mechanisms, important metabolism and regulatory mechanisms of microorganisms, but also develop a series of genes closely related to our lives on this basis. Engineering products include: vaccines for vaccination, new drugs for treatment, diagnostic reagents and various enzyme preparations used in industrial and agricultural production, etc. Through the transformation of genetic engineering methods, the construction of new strains and the transformation of traditional strains are promoted, and the advent of the era of microbial industry is comprehensively promoted. Industrial microorganisms involve many industries such as food, pharmaceuticals, metallurgy, mining, petroleum, leather, and light chemicals. The production of antibiotics, butanol, vitamin C and the preparation of some flavored foods through microbial fermentation; some special microbial enzymes are involved in leather depilation, metallurgy, oil mining and other production processes, and even directly used as additives for washing powder, etc.; there are also some Metabolites of microorganisms can be widely used in agricultural production as natural microbial pesticides. By studying the genome of Bacillus subtilis, a series of genes related to the production of antibiotics and important industrial enzymes were discovered. Lactobacilli serve as an important microecological regulator and participate in the food fermentation process.
Edit this paragraph World status
Before humans discovered and studied microorganisms, they divided all living things into two distinct kingdoms - the animal kingdom and the plant kingdom. As people's understanding of microorganisms gradually deepened, the two-kingdom system went through the three-kingdom system, the four-kingdom system, the five-kingdom system and even the six-kingdom system. It was not until the late 1970s that Americans Woese and others discovered the third life form on the earth - Archaea led to the birth of the three-domain theory of life. This theory holds that life is composed of Archaea, Bacteria and Eukarya. In the diagram "Phylogenetic tree of organisms", the yellow branch on the left is the bacterial domain; the brown and purple branches in the middle are the archaeal domain; and the green branch on the right is the eukaryotic domain. The Archaeal domain includes Crenarchaeota, Euryarchaeota and Korarchaeota; the Bacterial domain includes bacteria, actinomycetes, cyanobacteria and various other species other than Archaea. Prokaryotes; the eukaryotic domain includes fungi, protists, animals, and plants. Except for animals and plants, most other living things belong to the category of microorganisms. It can be seen that microorganisms occupy a particularly important position in the classification of biological kingdoms. The evolution of life has always been a hot topic of concern. Based on the "Cenancestor" evolutionary tree of life constructed by Brown et al. based on paralogous genes, they believe that the common ancestor of life, Cenancestor, was a protist.
During the evolution process, protists produced two branches, one is prokaryotes (bacteria and archaea), and the other is proto-eukaryotes. In the subsequent evolutionary process, bacteria and archaea first evolved in different directions, and then proto-eukaryotes Eukaryotes are created when an organism eats an archaea and replaces the host's RNA genome with the archaea's DNA. From an evolutionary perspective, microorganisms are the ancestors of all living things. If we compare the age of the earth to one year, microorganisms were born around March 20, and humans appeared on the earth around 7 pm on December 31! !
Benefits and harms! !