Bacteria are one of the main groups of organisms and belong to the field of bacteria. Bacteria are the most abundant of all living things, and its total number is estimated to be about 5× 10 to the thirtieth power. Bacteria are very small, the smallest known bacteria are only 0.2 micron long, so most bacteria can only be seen under a microscope. Bacteria are generally single-celled, with simple cell structure, lacking nucleus, cytoskeleton and membranous organelles, such as mitochondria and chloroplasts. According to these characteristics, bacteria belong to prokaryotes. There is another kind of organism in prokaryotes called archaea, which is a new category created by scientists according to their evolutionary relationship. For the sake of distinction, this creature is also called eubacteria.
Bacteria are widely distributed in soil and water, or live with other organisms. The human body also carries quite a lot of bacteria. It is estimated that the total number of bacterial cells in human body and epidermis is about ten times that of human body. In addition, some species are distributed in extreme environments, such as hot springs and even radioactive waste. They are classified as extreme microorganisms, and one of the most famous species is Thermotoga maritima, which was discovered by scientists in an undersea volcano in Italy. However, there are so many kinds of bacteria that scientists have only studied a few of them and named them. Of all the doors in the field of bacteria, only about half contain species that can be cultured in the laboratory.
There are two nutritional modes of bacteria: autotrophic and heterotrophic, among which heterotrophic saprophytic bacteria are important decomposers in the ecosystem, which makes the carbon cycle go smoothly. Some bacteria will carry out nitrogen fixation to transform nitrogen into a form that can be used by organisms.
Classification status
Field: the field of bacteria
Door:
Aquaculture fungi
Thermophylum
Thermal desulfurization bacteria
Singular cocci, a phylum of abnormal cocci
A gold-producing bacterium
Chlorophylum; chlorophylum
Thermo-microorganism
Nitrifying spirillum; nitrifying spirillum
Iron-removing animals, iron-removing animals.
Cyanophyta
Chloramphenicol bismuth chloride
Proteus, Proteus
Thick-walled door
Actinomyces, actinomycetes
Plankton, a floating mold
chlamydia
Spirogyra of the genus Spirogyra
Fibrobacteria phylum
Acidosporium
Bacteroides
flavobacterium
Sphingosine bacteria of sphingolipids
Fusobacterium， Knorr 1922
Microbacteria verrucosa, a phylum of Microbacteria verrucosa.
Reticulate nematodes
Gemmatimonadettes, gemmatimonadettes gate
Study history
The word bacteria was first put forward by German scientist Ehrenberg (1795- 1876) in 1828 to refer to a certain kind of bacteria. This word comes from the Greek β α κ ρ ι ν, which means "small stick".
1866, German zoologist haeckel (1834- 19 19) suggested using "protozoa", including all unicellular organisms (bacteria, algae, fungi and protozoa).
1878, French surgeon Charles Emanuel Zedillo (1804- 1883) put forward "microorganism" to describe bacterial cells or, more generally, tiny organisms.
Because bacteria are unicellular microorganisms, they are invisible to the naked eye and need to be observed with a microscope. 1683, Antony van Leeuwenhoek (1632–1723) observed bacteria for the first time with his own Dan Toujing microscope, and the microscope was enlarged by about 200 times. Louis Pasteur (1822- 1895) and robert koch (1843- 19 10) pointed out that bacteria can cause diseases.
Morphogenesis
Bacillus, cocci, spirillum and vibrio have different shapes, but they are mainly composed of the following structures.
(1) cell wall
The thickness of cell wall varies with bacteria, and is generally 15-30nm. The main component is peptidoglycan, which is a disaccharide unit composed of N- acetylglucosamine and N- acetylmuramic acid, and is connected into macromolecules by β( 1-4) glycosidic bond. N- acetyl muramic acid molecules have tetrapeptide side chains, and short peptides between adjacent polysaccharide fibers are bridged by peptide bridges (Gram-positive bacteria) or peptide bonds (Gram-negative bacteria) to form peptidoglycan sheets, which are glued into multiple layers like plywood.
The polysaccharide chain in peptidoglycan is the same in all species, but the transverse short peptide chain is different among species. The cell wall of Gram-positive bacteria is about 20-80 nm thick, and there are 15-50 layers of peptidoglycan, each layer is 1nm thick, containing 20-40% phosphomuramic acid and a little protein. The cell wall of Gram-negative bacteria is about 10nm thick, with only 2-3 layers of peptidoglycan. Other components are complex, including lipopolysaccharide, bacterial outer membrane and lipoprotein from outside to inside. In addition, there is a gap between the outer membrane and the cells.
Peptidoglycan is the main component of the cell wall of Gram-positive bacteria, and all substances that can destroy the structure of peptidoglycan or inhibit its synthesis have antibacterial or bactericidal effects. For example, lysozyme is N- acetyl lysozyme, and penicillin inhibits the activity of transpeptidase and the formation of peptide bridge.
The functions of bacterial cell wall include: keeping cell shape; Inhibit mechanical and osmotic damage (the cell wall of Gram-positive bacteria can bear the pressure of 20kg/cm2); Mediate the interaction between cells (invade the host); Prevent the invasion of macromolecules; Assist cell movement and division.
Cells with desquamation are called bacterial protoplasts or spherules, and the viability and activity of bacterial protoplasts are greatly reduced after desquamation.
(2) Cell membrane
It is a typical cell membrane structure with a thickness of about 8~ 10nm, and the outer side is close to the cell wall. Some gram-negative bacteria also have outer membranes. There is usually no endomembrane system, and there are no other organelles similar to eukaryotic cells except ribosomes. The electron transport chain of respiration and photosynthesis is located on the cell membrane. In some prokaryotes (cyanobacteria and purple bacteria) engaged in photosynthesis, the plasma membrane folds to form the inner membrane with pigment, which is related to the light capture reaction. The plasma membrane of some Gram-positive bacteria folds to form small tubular structures, which are called intermediates or intermediates (Figure 3- 1 1). Intermediate body enlarges the surface area of cell membrane and improves metabolic efficiency, which is called chondroid, and may also be related to DNA replication.
(3) Cytoplasm and nucleosome
Like other prokaryotes, bacteria have no nuclear membrane, and DNA is concentrated in the low electron density region of cytoplasm, which is called nuclear region or nucleosome. Bacteria generally have 1-4 nucleosomes, up to 20. Nucleosomes are circular double-stranded DNA molecules, which contain 2000 ~ 3000 kinds of protein. Their spatial structure is very simple and there are no introns. Because there is no nuclear membrane, DNA replication, RNA transcription and protein synthesis can be carried out at the same time, unlike the strict separation of eukaryotic cells in time and space.
Each bacterial cell contains about 5000 ~ 50000 ribosomes, some of which are attached to the cell membrane and most of which are free in the cytoplasm. The sedimentation coefficient of bacterial ribosomes is 70S, which consists of a large subunit (50S) and a small subunit (30S). The large subunit contains 23SrRNA, 5SrRNA and more than 30 kinds of protein, while the small subunit contains 16SrRNA and more than 20 kinds of protein. The small subunit of 30S is sensitive to tetracycline and streptomycin, and the large subunit of 50S is sensitive to erythromycin and chloramphenicol.
A genetic factor other than DNA in bacterial nuclear region that can replicate autonomously is called plasmid. Plasmids are naked circular double-stranded DNA molecules, containing 2~200 genes, which can replicate themselves and sometimes integrate into nuclear DNA. Plasmid DNA is very important in genetic engineering research and is often used as a carrier for gene recombination and gene transfer.
Cytoplasmic granules are granules in cytoplasm, which play the role of temporarily storing nutrients, including polysaccharides, lipids and polyphosphates.
(4) Other structures
The outermost surface of many bacteria is covered with a layer of polysaccharide, the obvious boundary is called capsule, such as pneumococcus, and the unclear boundary is called mucus layer, such as staphylococcus. Capsule is of great significance to the survival of bacteria, not only can it be used to resist bad environment; Protect yourself from white blood cells; But also can selectively adhere to the surface of specific cells, showing specific attack ability on target cells. For example, Salmonella typhi can specifically invade intestinal lymphoid tissue. The fiber of bacterial capsule can also store digestive enzymes secreted by bacteria, which can be used to attack target cells.
Flagella is the motor organ of some bacteria, which is composed of an elastin called flagellin, which is different from the flagella of eukaryotes in structure. Bacteria can change their motion state by adjusting the direction of flagella rotation (clockwise and counterclockwise).
Fimbriae are thin and short hard filaments on the surface of some bacteria, which need to be observed by electron microscope. The characteristics are: thin, short, straight, hard and numerous, and the pili has nothing to do with bacterial movement. According to the shape, structure and function, it can be divided into two types: ordinary fimbriae and sexual fimbriae. The former is related to bacterial adsorption and infection of the host, and the latter is a hollow tube, which is related to the transmission of genetic material.
kind
Bacteria can be classified in different ways. Bacteria have different shapes. Most bacteria are divided into the following three categories: bacilli are rod-shaped; The cocci are spherical (such as streptococcus or staphylococcus); Spirillum is spiral. The other is Vibrio, which is comma-shaped.
The structure of bacteria is very simple. Prokaryotes have no membrane organelles such as mitochondria and chloroplasts, but have cell walls. According to the composition of cell wall, bacteria can be divided into gram-positive bacteria and gram-negative bacteria. Gram comes from Danish bacteriologist Hans Christian Gram, who invented Gram staining.
Some bacteria have a capsule made of polysaccharide outside the cell wall, forming a cover or capsule. Capsules can help bacteria stay dormant in dry season, and can store food and dispose of waste.
The change of bacterial classification fundamentally reflects the change of development history, and many species even change or change their names frequently. In recent years, with the development of gene sequencing, genomics, bioinformatics and computational biology, bacteriology has been placed in a suitable position.
At first, except cyanobacteria (not classified as bacteria at all, but as blue-green algae), other bacteria were considered as a kind of fungi. With the discovery of their special prokaryotic cell structure, which is obviously different from other organisms (they are all eukaryotes), bacteria are classified as a single species and called prokaryotes, bacteria and monera kingdom at different times. It is generally believed that eukaryotes are derived from prokaryotes.
By studying the rRNA sequence, American microbiologist carl woese proposed in 1976 that prokaryotes include two groups. He called them eubacteria and archaea, and later renamed them bacteria and archaea. Woods pointed out that these two kinds of bacteria and eukaryotic cells are different species that originated from a primitive organism. Researchers have abandoned this model, but the three-domain system has gained universal recognition. In this way, bacteria can be divided into several fields, which are considered as one field in other systems. They are usually regarded as a single-source group, but this method is still controversial.
Archaea
Archaea (archaea or archaea) is a very special kind of bacteria, and most of them live in extreme ecological environment. It has some characteristics of prokaryotes, such as nuclear-free membrane and inner membrane system; It also has the characteristics of eukaryotes, such as the synthesis of protein from methionine, the insensitivity of ribosomes to chloramphenicol, the similarity between RNA polymerase and eukaryotic cells, and the combination of DNA with introns and histones. In addition, it also has different characteristics from prokaryotic cells and eukaryotic cells, such as: the lipid in the cell membrane is unsaponifiable; Cell walls contain no peptidoglycan, some are mainly protein, some contain heteropolysaccharide, and some are similar to peptidoglycan, but none contain muramic acid, D- amino acid and diaminopimelic acid.
type
Bacteria can reproduce asexually or through gene recombination. The most important way is binary division asexual reproduction: the cell wall of a bacterial cell divides laterally to form two daughter cells. And a single cell will also undergo genetic variation in the following ways: mutation (the genetic code of the cell itself changes randomly), transformation (unmodified DNA is transferred from one bacterium to another in solution), transfection (virus or bacterial DNA, or both DNA are transferred to another bacterium through phage), and bacterial conjugation (the DNA of one bacterium is transferred to another bacterium through a special protein structure formed between two bacteria). Bacteria can obtain DNA in these ways, then divide and pass on the recombinant genome to their offspring. Many bacteria contain plasmids containing extrachromosomal DNA.
When in a favorable environment, bacteria can form aggregates visible to the naked eye, such as flora.
Bacteria reproduce by binary division. Endospore, also known as spore, is a kind of dormant body with strong resistance to adverse environment when some bacteria are in unfavorable environment or the nutrition is exhausted. Because spores are formed in bacterial cells, they are often called endospore.
The vitality of spores is very tenacious. In some sediments at the bottom of the lake, Bacillus is still alive after 500- 1000 years, and the spores of Clostridium botulinum can tolerate boiling at 100℃ and pH 7.0 for 5-9.5 hours. Spores consist of the following parts from the inside out:
1. Spore protoplast (core): contains concentrated protoplasm.
2. Intima: It is formed by the cell membrane of the protogerm bacteria and surrounds the spore protoplasm.
3. spore wall: composed of peptidoglycan of reproductive bacteria, surrounding the inner membrane. It becomes the cell wall of bacteria after germination.
4. Cortex: It is the thickest layer in spore coat, which is composed of peptidoglycan, but its structure is different from that of cell wall, with less cross-linking. The polysaccharide scaffold is composed of cell wall anhydride instead of cell wall acid, and the tetrapeptide side chain is composed of L-Ala.
5. Outer membrane: It is also formed by bacterial cell membrane.
6. envelope: spore shell, tough and dense in texture, composed of keratin, containing a large number of disulfide bonds, with hydrophobic characteristics.
7. Spore outer membrane: Spore cover, that is, the outermost layer of spores, is composed of lipoprotein and carbohydrate (sugar) with loose structure.
To metabolize.
Bacteria have many different metabolic patterns. Some bacteria only need carbon dioxide as a carbon source and are called autotrophs. Those who get energy from light through photosynthesis are called photosynthetic autotrophs. Those who rely on oxidized compounds for energy are called chemoautotrophs. Other bacteria rely on organic carbon as carbon source, which is called heterotrophic bacteria.
Photosynthetic autotrophic bacteria include cyanobacteria, which are the oldest known organisms and may play an important role in producing oxygen in the earth's atmosphere. Other photosynthetic bacteria carry out some processes that do not produce oxygen. Include green sulfur bacteria, green non-sulfur bacteria, purple sulfur bacteria, purple non-sulfur bacteria and Heliobacter.
Nutrients required for normal growth include nitrogen, sulfur, phosphorus, vitamins and metal elements such as sodium, potassium, calcium, magnesium, iron, zinc and cobalt.
According to their reaction to oxygen, most bacteria can be divided into the following three categories: some can only grow under aerobic conditions, called aerobic bacteria; Others can only grow under anaerobic conditions, called anaerobic bacteria; Some facultative anaerobic bacteria can grow under aerobic or anaerobic conditions. Bacteria can also thrive in what humans consider extreme environments. This creature is called an extremophile. Some bacteria exist in hot springs and are called thermophilic bacteria; Others live in high salt lakes and are called halophilic microorganisms; Other bacteria exist in acidic or alkaline environment and are called acidophilic bacteria and alkalophilic bacteria. Others exist in alpine glaciers and are called psychrophilic bacteria.
sports
Moving bacteria can move by flagella, bacteria sliding or changing buoyancy. Another kind of bacteria, spirochete, has some flagella-like structures called axoneme, which connect two cell membranes of periplasm. When they move, their bodies take on a twisted spiral shape. Spirillum has no axoneme, but flagella.
The flagella of bacteria are arranged in different ways. Bacteria can have a polar flagella at one end, or a cluster of flagella. Peripheric organisms have scattered flagella on their surfaces.
Sports bacteria can be attracted or repelled by specific stimuli, which is called chemotaxis, such as chemotaxis, phototaxis and mechanism. In a special kind of bacteria-myxobacteria, individual bacteria attract each other and gather together to form fruiting bodies.
Use and harm
Bacteria are both useful and harmful to the environment, human beings and animals. Some bacteria become pathogens, leading to tetanus, typhoid fever, pneumonia, syphilis, cholera and tuberculosis. In plants, bacteria cause leaf spot, fire blight and wilting. Infection modes include contact, air transmission, food, water and microorganisms carrying bacteria. Pathogens can be treated with antibiotics and can be divided into bactericidal and bacteriostatic types.
Bacteria are usually used in fermented food together with yeast and other kinds of fungi. For example, in the traditional manufacturing process of vinegar, acetic acid bacteria in the air are used to convert alcohol into vinegar. Other foods made by bacteria include cheese, pickles, soy sauce, vinegar, wine, yogurt and so on. Bacteria can also secrete a variety of antibiotics, for example, streptomycin is secreted by hyphomycetes.
The ability of bacteria to degrade many organic compounds is often used to remove pollution, which is called bioremediation. For example, scientists use methane-oxidizing bacteria to decompose trichloroethylene and tetrachloroethylene pollution in Georgia, USA.
Bacteria also have a great influence on human activities. On the one hand, bacteria are the pathogens of many diseases, including tuberculosis, gonorrhea, anthrax, syphilis, plague and trachoma. However, human beings often use bacteria, such as the production of cheese and yogurt, the manufacture of some antibiotics, the treatment of wastewater and so on. These are all related to bacteria. Bacteria are widely used in biotechnology.
(A) bacterial power generation
Biologists predict that 2 1 century will be the era when bacteria generate electricity to benefit mankind. Speaking of bacterial power generation, it can be traced back to 19 10. British botanists successfully manufactured the world's first bacterial battery by using platinum as an electrode and putting it into the culture solution of Escherichia coli. 1984, American scientists designed a bacterial battery for spacecraft. The active substances of its electrodes are astronaut urine and living bacteria. However, the discharge efficiency of bacterial batteries at that time was low. It was not until the late 1980s that a major breakthrough was made in bacterial power generation. British chemists let bacteria break down the molecules in the battery pack and release electrons to move to the anode to generate electricity. The method is to add some aromatic compounds, such as dyes, to sugar solution as diluents to improve the ability of biological system to transfer electrons. During the period of bacterial power generation, the battery should be continuously inflated to stir the mixture of bacterial culture solution and oxidizing substances. According to calculation, using this bacterial battery, you can get 65,438+0,352,930 coulombs of electricity per 65,438+000 grams of sugar, and its efficiency can reach 40%, which is much higher than the batteries currently used, and there is still 65,438+00% potential to be tapped. As long as you keep adding sugar to the battery, you can get 2 amps of current, and it can last for several months.
Using the principle of bacterial power generation, bacterial power stations can also be established. A container with 100 cubic meter is filled with bacterial culture solution, and a bacterial power station with 1000 kW can be built. Sugar consumption is 200 Jin per hour, and the cost of power generation is higher. However, this is a "green" power station that will not pollute the environment. Moreover, after the development of technology, sugar solution can be completely replaced by hydrolysate of waste organic matter such as sawdust, straw and fallen leaves.
Now, developed countries such as the Eight Immortals have demonstrated their magical power: the United States has designed a comprehensive bacterial battery, in which single-celled algae first use sunlight to convert carbon dioxide and water into sugar, and then bacteria use these sugars to generate electricity; In Japan, two kinds of bacteria were put into the special syrup for batteries, so that one kind of bacteria swallowed the syrup to produce acetic acid and organic acid, and the other kind of bacteria converted these acids into hydrogen, which entered the phosphoric acid fuel cell to generate electricity; Britain invented a bacterial battery with methanol as the battery solution and platinum alcohol dehydrogenase as the electrode.
Now, all kinds of bacterial batteries have come out one after another. For example, there is a comprehensive bacterial battery. First, single-celled algae in the battery use sunlight to convert carbon dioxide and water into sugar, and then bacteria use these sugars to generate electricity. Another kind of bacterial battery is to put two kinds of bacteria into the special syrup of the battery, so that one kind of bacteria can swallow the syrup to produce acetic acid and organic acid, and then the other kind of bacteria can convert these acids into hydrogen, which can be used to enter the phosphoric acid fuel cell to generate electricity.
People are also surprised to find that bacteria also have the "special function" of capturing solar energy and converting it directly into electric energy. Recently, American scientists discovered a halophilic bacterium in the Dead Sea and the Great Salt Lake. They contain a purple pigment, which can generate electric charge when about 10% of sunlight is converted into chemicals. Scientists used them to make a small experimental solar bacterial cell, and the results proved that halophilic bacteria could be used to generate electricity, and the cost was greatly reduced by replacing sugar with salt. It can be seen that it is not a distant idea to let bacteria provide power for human beings, but a reality at hand.
(2) Bacteria are good for the stomach.
Bacteria in human large intestine survive by decomposing wastes in small intestine. Because these things are indigestible, the human system refuses to deal with them. These bacteria are equipped with a series of enzymes and metabolic channels. In this way, they can continue to decompose the remaining organic compounds. Most of them are devoted to the decomposition of carbohydrates in plants. Most bacteria in the large intestine are anaerobic, which means that they live without oxygen. Instead of breathing out and inhaling oxygen, they get energy by breaking down macromolecules of carbohydrates into small fatty acid molecules and carbon dioxide. This process is called "fermentation".
Some fatty acids are reabsorbed through the intestinal wall of the large intestine, which will provide us with extra energy. The remaining fatty acids help bacteria grow rapidly. So fast that they can reproduce every 20 minutes. Because they synthesize more vitamins B and K than they need, they are very generous in providing extra vitamins to other creatures in the group and you, their host. Although you can't produce these vitamins yourself, you can rely on these bacteria that are very friendly to you to supply you continuously.
Scientists are just beginning to understand the complex relationship between different bacteria in this group and their interaction with human hosts. This is a dynamic system, and with the changes of the host's diet structure and age, this system also makes corresponding adjustments. As soon as you were born, you began to collect the bacteria of your choice in your body. When your diet changes from breast milk to milk and into different solid foods, new bacteria will dominate your body.
Bacteria accumulated on the wall of the large intestine are survivors after a difficult journey. From the mouth, through the small intestine, it is attacked by digestive enzymes and strong acids. Those bacteria who are safe and sound after completing the trip will encounter more obstacles when they arrive. In order to grow, they must compete with the bacteria that already live there for space and nutrition. Fortunately, these "friendly" bacteria can stick themselves to the wall of the large intestine in any available place very skillfully. Some of these friendly bacteria can produce acids and antibacterial compounds, called bacteriocins. These bacteriocins can help fight off those nasty bacteria.
Those friendly bacteria can control the number of more dangerous bacteria and increase people's interest in "pre-life" food. This food contains cultured bacteria, and yogurt is one of them. When you drink a bottle of yogurt, check the label to see which bacteria will be your next guest.
cultivate
Common bacterial culture medium
Formula 1 beef paste agar medium
0.3g of beef sauce, 0.0g of peptone/kloc-0, 0.5g of sodium chloride and 0.5g of agar/kloc-0,
Water 1000 ml
Add 100 ml water to the beaker, add beef paste, peptone and sodium chloride, mark the beaker with crayons, and heat it on the fire. After the ingredients in the beaker are dissolved, add agar and stir constantly to avoid sticking to the bottom. After the agar is completely dissolved, make up the water loss, adjust the pH value to 7.2 ~ 7.6 with 10% hydrochloric acid or 10% sodium hydroxide, subpackage in each test tube, add cotton plugs, and sterilize with high pressure steam for 30 minutes.
Formula II potato culture medium
Take 250g of fresh beef heart (excluding fat and blood vessels), finely chop it into minced meat with a knife, and then add 500ml of distilled water and 5g of peptone. Mark the beaker, boil and simmer for 2 hours. Filtering, drying the filtered minced meat, and adjusting the pH value of the filtrate to about 7.5. Add 10 ml broth and a small amount of bovine heartbreak to each test tube and sterilize for later use.
Preparing rhizobia culture medium
Glucose 10g dipotassium hydrogen phosphate 0.5g
3 grams of calcium carbonate and 0.2 grams of magnesium sulfate.
0.4g yeast powder and 20g agar.
Water 1000ml 1% crystal violet solution 1ml.
Firstly, agar is boiled and dissolved in water, then other components are added, stirred and dissolved, and then packaged and sterilized for later use.