What types of bacteria exist. Examples of bacteria and their features. Who lives in the gut
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Science and life // Illustrations
Staphylococcus aureus.
Spirilla.
Trypanosoma.
Rotaviruses.
Rickettsia.
Yersinia.
Leishmania.
Salmonella.
Legionella.
Even 3,000 years ago, the great Greek Hippocrates guessed that contagious diseases are caused and carried by living beings. He called them miasma. But the human eye could not distinguish them. At the end of the 17th century, the Dutchman A. Leeuwenhoek created a sufficiently powerful microscope, and only then was it possible to describe and draw a variety of forms of bacteria - single-celled organisms, many of which are the causative agents of various human infectious diseases. Bacteria is one of the types of microbes (“microbe” - from the Greek “micros” - small and “bios” - life), however, the most numerous.
After the discovery of microbes and the study of their role in human life, it turned out that the world of these smallest organisms is very diverse and requires a certain systematization and classification. And today, experts use a system according to which the first word in the name of a microorganism means the genus, and the second - the species name of the microbe. These names (usually Latin or Greek) are "speaking". Thus, the name of some microorganisms reflects some of the most striking features of their structure, in particular, the form. This group primarily includes bacteria. In form, all bacteria are divided into spherical - cocci, rod-shaped - actually bacteria and convoluted - spirilla and vibrios.
globular bacteria- pathogenic cocci (from the Greek "coccus" - grain, berry), microorganisms that differ from each other in the location of cells after their division.
The most common of them are:
- staphylococci(from the Greek "stafile" - a bunch of grapes and "kokkus" - a grain, a berry), which received such a name because of the characteristic shape - a cluster resembling a bunch of grapes. The type of these bacteria has the most pathogenic effect. staphylococcus aureus(“Staphylococcus aureus”, as it forms clusters of golden color), causing various purulent diseases and food intoxications;
- streptococci(from the Greek "streptos" - a chain), whose cells after division do not diverge, but form a chain. These bacteria are the causative agents of various inflammatory diseases (tonsillitis, bronchopneumonia, otitis media, endocarditis, and others).
rod-shaped bacteria, or rods,- these are microorganisms of a cylindrical shape (from the Greek "bacterion" - a stick). From their name came the name of all such microorganisms. But those bacteria that form spores (a protective layer that protects against adverse environmental influences) are called bacilli(from the Latin "bacillum" - a stick). The spore-forming rods include the anthrax bacillus, a terrible disease known since ancient times.
The twisted shapes of bacteria are spirals. For example, spirilla(from Latin "spira" - bend) are bacteria that have the form of spirally curved rods with two or three curls. These are harmless microbes, with the exception of the causative agent of "rat bite disease" (Sudoku) in humans.
A peculiar form is also reflected in the name of microorganisms belonging to the family spirochete(from Latin "spira" - bend and "hate" - mane). For example, members of the family leptospira are distinguished by an unusual shape in the form of a thin thread with small, closely spaced curls, which makes them look like a thin twisted spiral. And the very name "leptospira" is translated as such - "narrow spiral" or "narrow curl" (from the Greek "leptos" - narrow and "spera" - gyrus, curl).
corynebacteria(causative agents of diphtheria and listeriosis) have characteristic club-shaped thickenings at the ends, as indicated by the name of these microorganisms: from lat. "korine" - a mace.
Today all known viruses also grouped into genera and families, including on the basis of their structure. Viruses are so small that in order to see them through a microscope, it must be much stronger than a conventional optical one. An electron microscope magnifies hundreds of thousands of times. Rotaviruses got its name from the Latin word "rota" - a wheel, since virus particles under an electron microscope look like small wheels with a thick sleeve, short spokes and a thin rim.
And the name of the family coronaviruses due to the presence of villi, which are attached to the virion through a narrow stem and expand towards the distant end, resembling the solar corona during an eclipse.
The name of some microorganisms is associated with the name of the organ they infect or the disease they cause. For example, title "meningococci" It is formed from two Greek words: “meningos” - the meninges, since these microbes mainly affect it, and “coccus” - a grain, indicating that they belong to spherical bacteria - cocci. The name is derived from the Greek word "pneumon" (lung). "pneumococci" These bacteria cause lung disease. Rhinoviruses- causative agents of a contagious rhinitis, hence the name (from the Greek "rhinos" - nose).
The origin of the name of a number of microorganisms is also due to their other most characteristic features. So, a distinctive feature of vibrios - bacteria in the form of a short curved rod - the ability to rapid oscillatory movements. Their name is derived from the French word vibrator- vibrate, vibrate, vibrate. Among the vibrios, the causative agent of cholera, which is called "cholera vibrio", is the most famous.
Bacteria of the genus proteus(Proteus) refer to the so-called microbes that are dangerous for some, but not for others. In this regard, they were named after the sea deity from ancient Greek mythology - Proteus, who was credited with the ability to arbitrarily change his appearance.
Monuments are erected to great scientists. But sometimes the names of microorganisms discovered by them also become monuments. For example, microorganisms that occupy an intermediate position between viruses and bacteria have been named "rickettsia" in honor of the American explorer Howard Taylor Ricketts (1871-1910), who died of typhus while studying the causative agent of this disease.
The causative agents of dysentery were thoroughly studied by the Japanese scientist K. Shiga in 1898, in his honor they subsequently received their generic name - "shigella".
Brucella(causative agents of brucellosis) are named after the English military doctor D. Bruce, who in 1886 for the first time managed to isolate these bacteria.
Bacteria grouped in a genus "yersinia", named after the famous Swiss scientist A. Yersin, who discovered, in particular, the causative agent of the plague - Yersinia pestis.
By the name of the English doctor V. Leishman, the simplest unicellular organisms (causative agents of leishmaniasis) are named leishmania, described in detail in 1903.
The generic name is associated with the name of the American pathologist D. Salmon "salmonella", a rod-shaped intestinal bacterium that causes diseases such as salmonellosis and typhoid fever.
And the German scientist T. Escherich owe their name Escherichia- Escherichia coli, first isolated and described by him in 1886.
In the origin of the name of some microorganisms, a certain role was played by the circumstances under which they were discovered. For example, generic name "legionella" appeared after an outbreak in 1976 in Philadelphia among the delegates of the convention of the American Legion (an organization that unites US citizens - participants in international wars) of a severe respiratory disease caused by these bacteria - they were transmitted through the air conditioner. A coxsackie viruses were first isolated from children with polio in 1948 in the village of Coxsackie (USA), hence the name.
are typical prokaryotic organisms. Bacteria are the oldest inhabitants of the earth, they have been living for two billion years. Scientists know about 2,500 species. Bacteria have but do not have a nucleus separated by a membrane from the cytoplasm.
The genetic material in bacteria represented by finger DNA molecules about 1 mm long. Each such molecule consists of about 5,000,000 base pairs. The plasma membrane of a bacterial cell does not differ in structure and function from that of a eukaryotic cell. In some bacteria, the plasma membrane bulges inward and lysosomes are formed - their main function is respiration. Ribosomes in a bacterial cell are scattered throughout the cytoplasm. On the cell wall of some bacteria there are rod-shaped protein protrusions - they are necessary for attaching cells to each other. The cell wall gives the bacterial cell rigidity and shape. Some bacteria have mucous layers - capsules. They serve as additional protection for cells.
Majority bacteria does not contain chlorophyll and feeds on ready-made organic substances - heterotrophically. Bacteria have mastered all habitats. They live almost everywhere: in the soil, in dust, in the air, in water, on the body of animals, inside living organisms. They remain viable in hot springs at a temperature of 90 degrees C, in oil wells at a depth of 1,700 meters, at the bottom of the ocean - deeper than 10 kilometers. Some bacteria survive five days of boiling under vacuum. Many bacteria can live without oxygen. The number of bacteria is huge: in one gram of soil there can be up to 2 billion bacteria.
They are diverse in shape: spherical (cocci), rod-shaped (), curved (vibrios), spiral (spirilla), in the form of a chain (streptococci), in the form of clusters (staphylococci). Some bacteria have flagella.
They multiply very quickly, every 20-30 minutes. Theoretically, their numbers are growing exponentially. Reproduction is limited by climatic conditions, the action of sunlight, between species, the accumulation of metabolic products. Under optimal conditions, the bacterial cell grows at a tremendous rate. Having reached a certain size, the bacterial cell proceeds to asexual, before dividing, doubling of the material occurs. The fastest growing bacteria divide every 20 minutes.
Saprophytes feed on dead organic matter, decompose organic remains together with fungi, being decomposers of any ecosystem. Among them are putrefactive bacteria, fermentation bacteria.
Symbiotic bacteria live on the roots of plants and supply them with nitrogen, which only bacteria can absorb.
Intestinal bacteria ensure normal functioning.
They are very important for a person. This is due to the role of microorganisms in.
Soil fertility. During the vital activity of soil bacteria, the formation of humus occurs, which is an organic matter decomposed with the help of bacteria, containing all the necessary substances for plant life. In addition, soil bacteria are involved in the cycle of various substances. For example, nitrogen.
Cleaning of drains. Microorganisms are used for wastewater treatment, which in a short time can convert most organic compounds into inorganic ones.
Bacteria are symbionts. In the intestines of many animals and humans, the so-called microflora lives, which is able to digest the food consumed by the body and synthesize vitamins.
Industrial fermentation. Through fermentation, a person can receive various substances, for example, acetic acid, silage, alcohol, fermented milk products.
Production of antibiotics. These substances are secreted by some bacteria and fungi. These substances inhibit the activity of other bacteria.
Feed protein production.
Enzyme production and genetic engineering. The ability to industrially produce insulin, obtain alcohols, ketones, organic acids, polymeric substances.
Biological pest control methods, various bacteria can infect and cause death of agricultural pests.
Bacteria is the most ancient organism on earth, as well as the simplest in its structure. It consists of only one cell, which can only be seen and studied under a microscope. A characteristic feature of bacteria is the absence of a nucleus, which is why bacteria are classified as prokaryotes.
Some species form small groups of cells; such clusters may be surrounded by a capsule (sheath). The size, shape, and color of bacteria are highly dependent on the environment.
In terms of shape, bacteria are divided into: rod-shaped (bacilli), spherical (cocci) and convoluted (spirilla). There are also modified ones - cubic, C-shaped, star-shaped. Their sizes range from 1 to 10 microns. Certain types of bacteria can actively move with the help of flagella. The latter sometimes exceed the size of the bacterium itself twice.
Types of bacteria forms
For movement, bacteria use flagella, the number of which is different - one, a pair, a bundle of flagella. The location of the flagella is also different - on one side of the cell, on the sides, or evenly distributed over the entire plane. Also, one of the ways of movement is considered to be sliding due to the mucus that the prokaryote is covered with. Most have vacuoles inside the cytoplasm. Adjusting the capacity of the gas in the vacuoles helps them move up or down in the liquid, as well as move through the air channels of the soil.
Scientists have discovered more than 10 thousand varieties of bacteria, but according to the assumptions of scientific researchers, there are more than a million species of them in the world. The general characteristics of bacteria makes it possible to determine their role in the biosphere, as well as to study the structure, types and classification of the bacterial kingdom.
habitats
The simplicity of the structure and the speed of adaptation to environmental conditions helped bacteria to spread over a wide range of our planet. They exist everywhere: water, soil, air, living organisms - all this is the most acceptable habitat for prokaryotes.
Bacteria have been found both at the south pole and in geysers. They are on the ocean floor, as well as in the upper layers of the Earth's air shell. Bacteria live everywhere, but their number depends on favorable conditions. For example, a large number of bacterial species live in open water bodies, as well as in the soil.
Structural features
A bacterial cell is distinguished not only by the fact that it does not have a nucleus, but also by the absence of mitochondria and plastids. The DNA of this prokaryote is located in a special nuclear zone and has the form of a nucleoid closed in a ring. In bacteria, the cell structure consists of a cell wall, a capsule, a capsule-like membrane, flagella, pili, and a cytoplasmic membrane. The internal structure is formed by the cytoplasm, granules, mesosomes, ribosomes, plasmids, inclusions and nucleoid.
The bacterial cell wall performs the function of defense and support. Substances can freely flow through it due to permeability. This shell contains pectin and hemicellulose. Some bacteria secrete a special mucus that can help protect against drying out. Mucus forms a capsule - a polysaccharide in chemical composition. In this form, the bacterium is able to tolerate even very high temperatures. It also performs other functions, for example, sticking to any surfaces.
On the surface of the bacterial cell are thin protein villi - pili. There may be a large number of them. Pili help the cell to transfer genetic material, and also provide adhesion to other cells.
Under the plane of the wall is a three-layer cytoplasmic membrane. It guarantees the transport of substances, and also plays a significant role in the formation of spores.
The cytoplasm of bacteria is 75 percent made from water. The composition of the cytoplasm:
- fishsomes;
- mesosomes;
- amino acids;
- enzymes;
- pigments;
- sugar;
- granules and inclusions;
- nucleoid.
Metabolism in prokaryotes is possible, both with the participation of oxygen and without it. Most of them feed on ready-made nutrients of organic origin. Very few species are capable of synthesizing organic substances from inorganic ones themselves. These are blue-green bacteria and cyanobacteria, which played a significant role in shaping the atmosphere and saturating it with oxygen.
reproduction
In conditions favorable for reproduction, it is carried out by budding or vegetatively. Asexual reproduction occurs in the following sequence:
- The bacterial cell reaches its maximum volume and contains the necessary supply of nutrients.
- The cell lengthens, a partition appears in the middle.
- Within the cell, a division of the nucleotide occurs.
- DNA main and separated diverge.
- The cell is divided in half.
- Residual formation of daughter cells.
With this method of reproduction, there is no exchange of genetic information, so all daughter cells will be an exact copy of the mother.
The process of reproduction of bacteria in adverse conditions is more interesting. Scientists learned about the ability of bacteria to reproduce sexually relatively recently - in 1946. Bacteria do not have a division into female and germ cells. But they have different DNA. Two such cells, when approaching each other, form a channel for the transfer of DNA, an exchange of sites occurs - recombination. The process is quite long, the result of which are two completely new individuals.
Most bacteria are very difficult to see under a microscope because they do not have their own color. Few varieties are purple or green due to their content of bacteriochlorophyll and bacteriopurpurine. Although if we consider some colonies of bacteria, it becomes clear that they release colored substances into the environment and acquire a bright color. In order to study prokaryotes in more detail, they are stained.
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Classification
The classification of bacteria can be based on indicators such as:
- Form
- way to travel;
- way to get energy;
- waste products;
- degree of danger.
Bacteria symbionts live in partnership with other organisms.
Bacteria saprophytes live on already dead organisms, products and organic waste. They contribute to the processes of decay and fermentation.
Decay cleanses nature of corpses and other wastes of organic origin. Without the process of decay, there would be no cycle of substances in nature. So what is the role of bacteria in the cycling of matter?
Decay bacteria are an assistant in the process of breaking down protein compounds, as well as fats and other compounds containing nitrogen. Having carried out a complex chemical reaction, they break bonds between the molecules of organic organisms and capture protein molecules, amino acids. Splitting, the molecules release ammonia, hydrogen sulfide and other harmful substances. They are poisonous and can cause poisoning in humans and animals.
Decay bacteria multiply rapidly in favorable conditions for them. Since these are not only beneficial bacteria, but also harmful ones, in order to prevent premature decay in products, people have learned to process them: dry, pickle, salt, smoke. All of these treatments kill bacteria and prevent them from multiplying.
Fermentation bacteria with the help of enzymes are able to break down carbohydrates. People noticed this ability in ancient times and use such bacteria to make lactic acid products, vinegars, and other food products to this day.
Bacteria, working in conjunction with other organisms, do very important chemical work. It is very important to know what types of bacteria are and what benefits or harm they bring to nature.
Significance in nature and for man
The great importance of many types of bacteria (in the processes of putrefaction and various types of fermentation) has already been noted above; fulfillment of a sanitary role on Earth.
Bacteria also play a huge role in the cycle of carbon, oxygen, hydrogen, nitrogen, phosphorus, sulfur, calcium and other elements. Many types of bacteria contribute to the active fixation of atmospheric nitrogen and convert it into an organic form, contributing to an increase in soil fertility. Of particular importance are those bacteria that decompose cellulose, which are the main source of carbon for the vital activity of soil microorganisms.
Sulfate-reducing bacteria are involved in the formation of oil and hydrogen sulfide in therapeutic mud, soils and seas. Thus, the layer of water saturated with hydrogen sulfide in the Black Sea is the result of the vital activity of sulfate-reducing bacteria. The activity of these bacteria in soils leads to the formation of soda and soda salinization of the soil. Sulfate-reducing bacteria convert nutrients in rice plantation soils into a form that becomes available to the roots of the crop. These bacteria can cause corrosion of metal underground and underwater structures.
Thanks to the vital activity of bacteria, the soil is freed from many products and harmful organisms and saturated with valuable nutrients. Bactericidal preparations are successfully used to combat many types of insect pests (corn borer, etc.).
Many types of bacteria are used in various industries to produce acetone, ethyl and butyl alcohols, acetic acid, enzymes, hormones, vitamins, antibiotics, protein and vitamin preparations, etc.
Without bacteria, processes are impossible in tanning leather, drying tobacco leaves, making silk, rubber, processing cocoa, coffee, urinating hemp, flax and other bast-fiber plants, sauerkraut, sewage treatment, leaching metals, etc.
At this very moment, man, as you read these lines, you are benefiting from the work of bacteria. From the oxygen we breathe in to the nutrients our stomach extracts from food, we have bacteria to thank for thriving on this planet. There are about ten times more microorganisms in our body, including bacteria, than our own cells. In fact, we are more microbes than humans.
Only recently have we begun to slowly understand microscopic organisms and their impact on our planet and health, but history shows that centuries ago our ancestors used the power of bacteria to ferment food and drink (had anyone heard of bread and beer?).
In the 17th century, we began to study bacteria already directly in our bodies in close connection with us - in the mouth. Anthony van Leeuwenhoek's curiosity led to the discovery of the bacteria when he examined a plaque between his own teeth. Van Leeuwenhoek described bacteria poetically, describing the bacterial colony on his teeth as "a little white substance, like hardened dough". By placing the sample under a microscope, van Leeuwenhoek saw that the microorganisms were moving. So they are alive!
You should know that bacteria have played a pivotal role for the Earth, being the key to creating breathable air and the biological wealth of the planet we call home.
In this article, we will provide you with the big picture about these tiny but highly influential micro-organisms. We look at the good, the bad, and the downright bizarre ways that bacteria shape human and environmental history. First, let's look at how bacteria differ from other types of life.
Basics of bacteria
Well, if bacteria are invisible to the naked eye, how can we know so much about them?
Scientists have developed powerful microscopes to look at bacteria - which range in size from one to several microns (a millionth of a meter) - and find out how they relate to other life forms, plants, animals, viruses and fungi.
As you may know, cells are the building blocks of life, they make up both the tissues of our body and the tree that grows outside the window. Humans, animals and plants have cells with genetic information contained in a membrane called the nucleus. These types of cells, called eukaryotic cells, have special organelles, each of which performs a unique job in helping the cell to function.
Bacteria, however, do not have nuclei, and their genetic material (DNA) floats freely within the cell. These microscopic cells lack organelles and have other methods of reproducing and transferring genetic material. Bacteria are considered prokaryotic cells.
Do bacteria survive in an environment with or without oxygen?
Their shape: sticks (bacillus), circles (cocci) or spirals (spirillum)
Are the bacteria Gram-negative or Gram-positive, that is, do they have an outer protective membrane that prevents staining of the inside of the cell
How bacteria move and explore their environment (many bacteria have flagella, tiny whip-like structures that allow them to move around in their environment)
Microbiology - the science of all types of microbes, including bacteria, archaea, fungi, viruses, and protozoa - distinguishes bacteria from their microbial brethren.
The bacteria-like prokaryotes, now classified as archaea, once co-existed with bacteria, but as scientists learned more about them, they gave bacteria and archaea their own categories.
Microbial nutrition (and miasma)
Like humans, animals, and plants, bacteria need food to survive.
Some bacteria - autotrophs - use basic resources like sunlight, water, and chemicals from the environment to create food (think cyanobacteria, which turned sunlight into oxygen for 2.5 million years). Other bacteria are called heterotrophs by scientists because they draw energy from existing organic matter as food (for example, dead leaves on forest soil).
The truth is that what might be tasty to bacteria will be disgusting to us. They have evolved to absorb all types of products, from oil spills and by-products of nuclear fission to human waste and decay products.
But the affinity of bacteria for a particular food source could benefit society. For example, art experts in Italy have turned to bacteria that can eat excess layers of salt and glue that reduce the durability of priceless artwork. The ability of bacteria to process organic matter is also very useful for the Earth, both in soil and in water.
From daily experience, you are very familiar with the odor caused by bacteria ingesting the contents of your wastebasket, digesting leftover food, and releasing their own gaseous by-products. However, everything is not limited to this. You can also blame bacteria for causing those awkward moments when you yourself pass gases.
One big family
Bacteria grow and form colonies when given the chance. If food and environmental conditions are favorable, they multiply and form sticky clumps, called biofilms, to survive on surfaces ranging from rocks to your mouth's teeth.
Biofilms have their pros and cons. On the one hand, they are mutually beneficial to natural objects (mutualism). On the other hand, they can be a serious threat. For example, doctors who treat patients with medical implants and devices are seriously concerned about biofilms, as they are real estate for bacteria. Once colonized, biofilms can produce by-products that are toxic - and sometimes fatal - to humans.
Like people in cities, the cells in the biofilm communicate with each other, exchanging information about food and potential danger. But instead of calling neighbors on the phone, bacteria send notes using chemicals.
Also, bacteria are not afraid to live on their own. Some species have developed interesting ways to survive in harsh environments. When there is no more food, and conditions become unbearable, the bacteria preserve themselves by creating a tough shell - the endospore, which puts the cell into a dormant state and preserves the genetic material of the bacterium.
Scientists find bacteria in such time capsules that have been stored for 100 or even 250 million years. This suggests that the bacteria can self-storage for a long time.
Now that we know what opportunities colonies provide for bacteria, let's figure out how they get there - by dividing and multiplying.
Reproduction of bacteria
How do bacteria create colonies? Like other life forms on Earth, bacteria need to copy themselves in order to survive. Other organisms do this through sexual reproduction, but not bacteria. But first, let's discuss why variety is good.
Life undergoes natural selection, or the selective forces of a certain environment allow one type to flourish and multiply more than another. You may remember that genes are the mechanism that instructs the cell what to do and determines what color your hair and eyes will be. You get genes from your parents. Sexual reproduction results in mutations, or random changes in DNA, which creates diversity. The greater the genetic diversity, the greater the chance that an organism will be able to adapt to environmental constraints.
For bacteria, reproduction does not depend on meeting the right microbe; they simply copy their own DNA and divide into two identical cells. This process, called binary fission, occurs when one bacterium divides into two, copying its DNA and passing it on to both parts of the split cell.
Since the resulting cell will eventually be identical to the one from which it was born, this method of reproduction is not the best for creating a diverse gene pool. How do bacteria acquire new genes?
It turns out that bacteria use a clever trick: horizontal gene transfer, or the exchange of genetic material without reproduction. There are several ways that bacteria use to do this. One method involves harvesting genetic material from the environment outside the cell - from other microbes and bacteria (through molecules called plasmids). Another way is viruses, which use bacteria as their home. By infecting a new bacterium, viruses leave the genetic material of the previous bacterium in the new one.
The exchange of genetic material gives bacteria the flexibility to adapt, and they adapt if they feel stressful changes in the environment, such as food shortages or chemical changes.
Understanding how bacteria adapt is essential to combat them and develop antibiotics in medicine. Bacteria can exchange genetic material so frequently that sometimes a treatment that worked before no longer works.
No high mountains, no great depth
If you ask the question “where are the bacteria?”, It is easier to ask “where are there no bacteria?”.
Bacteria are found almost everywhere on Earth. It is impossible to imagine the number of bacteria on the planet at the same time, but according to some estimates, their number is (bacteria and archaea together) 5 octillion - this is a number with 27 zeros.
The classification of bacterial species is extremely complex for obvious reasons. Now there are approximately 30,000 officially identified species, but the knowledge base is constantly growing, and there are opinions that we have just the tip of the iceberg for all types of bacteria.
The truth is that bacteria have been around for a very long time. They gave rise to some of the oldest fossils, which are 3.5 billion years old. The results of scientific research suggest that cyanobacteria began to create oxygen approximately 2.3-2.5 billion years ago in the world's oceans, saturating the Earth's atmosphere with oxygen that we breathe to this day.
Bacteria can survive in air, water, soil, ice, heat, plants, intestines, skin - everywhere.
Some bacteria are extremophiles, meaning they can withstand extreme environments where they are either extremely hot or cold or lack the nutrients and chemicals we normally associate with life. Researchers have found such bacteria in the Mariana Trench, the deepest point on Earth at the bottom of the Pacific Ocean, near hydrothermal vents in water and ice. There are also heat-loving bacteria, such as those that color the opalescent pool in Yellowstone National Park.
Bad (for us)
While bacteria make important contributions to human and planetary health, they also have a dark side. Some bacteria can be pathogenic, meaning they can cause illness and disease.
Throughout human history, certain bacteria have (understandably) gotten a bad rap for causing panic and hysteria. Take, for example, the plague. The plague-causing bacterium Yersinia pestis not only killed over 100 million people, but may have contributed to the collapse of the Roman Empire. Before the advent of antibiotics, drugs that help fight bacterial infections, they were very difficult to stop.
Even today, these pathogenic bacteria seriously scare us. Thanks to the development of antibiotic resistance, the bacteria that cause anthrax, pneumonia, meningitis, cholera, salmonellosis, tonsillitis and other diseases that still remain with us are always a danger to us.
This is especially true for Staphylococcus aureus, the bacterium responsible for staph infections. This "superbug" causes many problems in clinics, as patients quite often pick up this infection while inserting medical implants and catheters.
We have already talked about natural selection and how some bacteria produce a variety of genes that help them cope with environmental conditions. If you have an infection and some of the bacteria in your body are different from others, antibiotics can kill most of the bacterial population. But those bacteria that survive will develop resistance to the drug and stay, waiting for the next chance. Therefore, doctors recommend completing the course of antibiotics to the end, and in general, contacting them as rarely as possible, only as a last resort.
Bioweapons are another chilling aspect of this conversation. Bacteria can be used as a weapon in some cases, in particular, anthrax was used at one time. In addition, not only people suffer from bacteria. A separate species - Halomonas titanicae - showed an appetite for the sunken ocean liner Titanic, corroding the metal of the historic ship.
Of course, bacteria can bring more than just harm.
heroic bacteria
Let's explore the good side of bacteria. After all, these microbes gave us delicious foods like cheese, beer, sourdough, and other fermented items. They also improve human health and are used in medicine.
Individual bacteria can be thanked for shaping human evolution. Science is collecting more and more data about microflora - microorganisms that live in our bodies, especially in the digestive system and intestines. Research shows that bacteria, the new genetic materials, and the diversity they bring to our bodies allow humans to adapt to new food sources that weren't used before.
To put it another way, by lining the surface of your stomach and intestines, bacteria work for you. When you eat, bacteria and other microbes help you break down and extract nutrients from food, especially carbohydrates. The more diverse the bacteria we consume, the more diverse our bodies get.
Although our knowledge of our own microbes is very limited, there is reason to believe that the absence of certain microbes and bacteria in the body may be associated with health, metabolism and susceptibility to human allergens. Preliminary studies in mice have shown that metabolic diseases like obesity are associated with diversity and healthy microflora, rather than our prevailing “calories in, calories out” mindset.
The possibility of introducing certain microbes and bacteria into the human body, which can provide certain benefits, is now being actively explored, however, at the time of writing, general recommendations for their use have not yet been established.
In addition, bacteria have played an important role in the development of scientific thought and human medicine. Bacteria played a leading role in the development of Koch's postulates of 1884, which led to the general understanding that diseases are caused by a particular type of microbe.
Researchers studying bacteria accidentally discovered penicillin, an antibiotic that has saved countless lives. Also more recently, in this regard, an easy way to edit the genome of organisms has been discovered, which can revolutionize medicine.
In fact, we are just beginning to understand how to benefit from our cohabitation with these little friends. In addition, it is not clear who is the true owner of the Earth: people or microbes.
Speaking of bacteria, most often we represent something negative. Yet we know very little about them. The structure and vital activity of bacteria are quite primitive, but, according to some scientists, these are the most ancient inhabitants of the Earth, and for so many years they have not disappeared or died out. A person uses many types of such microorganisms for his own benefit, while others are the cause of serious diseases and even epidemics. But the harm of some bacteria is sometimes not commensurate with the benefits of others. Let's talk about these amazing microorganisms and get acquainted with their structure, physiology and classification.
Kingdom of bacteria
These are non-nuclear, most often unicellular microorganisms. Their discovery in 1676 is the merit of the Dutch scientist A. Leeuwenhoek, who first saw tiny bacteria under a microscope. But the study of their nature, physiology and role in human life was first begun by the French chemist and microbiologist Louis Pasteur in the 1850s. The structure of bacteria began to be actively studied with the advent of electron microscopes. Its cell consists of a cytoplasmic membrane, a ribosome and a nucleotide. The DNA of a bacterium is concentrated in one place (the nucleoplasm) and is a coil of thin threads. The cytoplasm is separated from the cell wall by a cytoplasmic membrane; it contains a nucleotide, various membrane systems, and cell inclusions. The ribosome of a bacterium consists of 60% RNA, the rest is protein. The photo below shows the structure of salmonella.
Cell wall and its components
Bacteria have a cellular structure. The cell wall has a thickness of about 20 nm and, unlike higher plants, does not have a fibrillar structure. Its strength is provided by a special cover called a bag. It consists mainly of a polymeric substance - murein. Its components (subunits) are connected in a certain sequence into special polyglycan strands. Together with short peptides, they form a macromolecule resembling a network. This is the murein bag.
Organs of locomotion
These microorganisms are capable of active movement. It is carried out due to plasma flagella, which have a helical structure. Bacteria can move at speeds up to 200 microns per second and turn around their axis 13 times per second. The ability of flagella to move is provided by a special contractile protein - flagellin (analogous to myosin in muscle cells).
They have the following dimensions: length - up to 20 microns, diameter - 10-20 nm. Each flagellum arises from a basal body, which is embedded in the bacterial cell wall. The organs of locomotion can be single or arranged in whole bundles, as, for example, in spirilla. The number of flagella may depend on environmental conditions. For example, Proteus vulgaris, with poor nutrition, has only two subpolar flagella, while under normal development conditions, there can be from 2 to 50 in bundles.
Movement of microorganisms
The structure of the bacterium (diagram below) is such that it can move quite actively. Movement in most cases occurs due to a push and is carried out mainly in a liquid or humid environment. Depending on the acting factor, in other words, the type of external stimulus, it can be:
- chemotaxis is the directed movement of a bacterium to nutrients or, conversely, away from any toxins;
- aerotaxis - movement towards oxygen (in aerobes) or away from it (in anaerobes);
- phototaxis - a reaction to light, manifested in movement, is characteristic primarily of phototrophs;
- magnetotaxis - a reaction to changes in the magnetic field, due to the presence of special particles (magnetosomes) in some microorganisms.
In one of the above ways, bacteria, the structural features of the cells of which allow them to move, can create clusters in places with optimal conditions for their vital activity. In addition to flagella, some species have numerous thinner filaments - they are called "fimbriae" or "pili", but their function has not yet been sufficiently studied. Bacteria that do not have special flagella are capable of gliding movement, however, it is characterized by a very low speed: approximately 250 microns per minute.
The second small group of bacteria are autotrophs. They are able to synthesize organic substances from inorganic substances, can partially assimilate atmospheric carbon dioxide and are chemotrophs. These bacteria occupy a very important place in the cycle of chemical elements in nature.
There are also two groups of true phototrophs. The structural features of bacteria of this category are that they contain a substance (pigment) bacteriochlorophyll, which is related in nature to plant chlorophyll, and since they lack photosystem II, photosynthesis proceeds without oxygen evolution.
Reproduction by division
The main method of reproduction is the division of the original mother cell in two (amitosis). For elongated shapes, this always occurs perpendicular to the longitudinal axis. In this case, the structure of the bacterium undergoes short-term changes: a transverse partition is formed from the edge of the cell to the middle, along which the parent organism is then divided. This explains the old name of the kingdom - Drobyanki. Cells after division can remain connected in unstable, loose chains.
These are the distinctive features of the structure of bacteria of some species, for example, streptococci.
Sporulation and sexual reproduction
The second method of reproduction is sporulation. It is directly related to the desire to adapt to adverse conditions and is aimed at surviving them. In some rod-shaped bacteria, spores are formed endogenously, that is, inside the cell. They are very resistant to heat and can be preserved even when boiled for a long time. Spore formation begins with various chemical reactions in the mother cell, degrading about 75% of all its proteins. Then division occurs. In this case, two daughter cells are formed. One of them (smaller) is covered with a thick shell, which can occupy up to 50% in volume - this is the spore. It remains viable and ready to germinate for 200-300 years.
Some species are capable of sexual reproduction. This process was first discovered in 1946, when the cell structure of the bacterium Escherichia coli was studied. It turned out that partial transfer of genetic material is possible. That is, DNA fragments are transferred from one cell (donor) to another (recipient) in the process of conjugation. This is done with the help of bacteriophages or by transformation.
The structure of the bacterium and the peculiarities of its physiology are such that, under ideal conditions, the division process occurs constantly and very quickly (every 20-30 minutes). But in the natural environment, it is limited by various factors (sunlight, nutrient medium, temperature, etc.).
The classification of these microorganisms is based on the different structure of the bacterial cell wall, which determines the preservation of the aniline dye in the cell or its leaching. This was identified by H. K. Gram, and subsequently, in accordance with his name, two large divisions of microorganisms were identified, which we will discuss below.
Gram-positive bacteria: features of the structure and vital activity
These microorganisms have a multi-layer murein cover (30-70% of the total dry mass of the cell wall), due to which aniline dye is not washed out of the cells (the structure of a gram-positive bacterium is schematically shown in the photo above on the left, and gram-negative bacteria on the right). Their feature is that diaminopimelic acid is often replaced by lysine. The protein content is much less, and polysaccharides are absent or linked by covalent bonds. All bacteria of this department are divided into several groups:
- Gram-positive cocci. They are single cells or groups of two, four or more cells (up to 64), held together by cellulose. By type of nutrition, these are, as a rule, obligate or facultative anaerobes, for example, lactic acid bacteria from the Streptococcal family, but aerobes can also be.
- Non-sporing sticks. By the name, you can already understand the structure of a bacterial cell. This group includes anaerobic or facultatively aerobic lactic acid species from the Lactobacillus family.
- Spore-forming sticks. They are represented by only one family - Clostridia. They are obligate anaerobes capable of producing spores. Many of them form characteristic chains or threads from individual cells.
- Corynemorphic microorganisms. The external structure of the bacterial cell of this group can vary significantly. So, sticks can become club-shaped, short, cocci or slightly branched forms. They do not form endospores. These include propionic acid, streptomycete bacteria, etc.
- Mycoplasmas. If you pay attention to the structure of the bacterium (the diagram in the figure below - the arrow points to the DNA chain), then it can be noted that it does not have a cell wall (instead of it there is a cytoplasmic membrane) and, therefore, does not stain with aniline dye, so it cannot be attributed to this section based on Gram staining. But according to recent studies, mycoplasmas originated from gram-positive microorganisms.
Gram-negative bacteria: functions, structure
In such microorganisms, the murein network is very thin, its share of the dry mass of the entire cell wall is only 10%, the rest is lipoproteins, lipopolysaccharides, etc. Substances that come with Gram staining are easily washed out. By type of nutrition, gram-negative bacteria are phototrophs or chemotrophs, some species are capable of photosynthesis. Classification within the department is in the process of formation, various families are combined into 12 groups, based on the characteristics of morphology, metabolism and other factors.
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The importance of bacteria for humans
Despite their seemingly invisibility, bacteria are of great importance for humans, both positive and negative. The production of many food products is impossible without the participation of individual representatives of this kingdom. The structure and vital activity of bacteria allow us to obtain many dairy products (cheeses, yogurts, kefir and much more). These microorganisms are involved in the processes of fermentation, fermentation.
Numerous types of bacteria are the causative agents of diseases in animals and humans, such as anthrax, tetanus, diphtheria, tuberculosis, plague, etc. But at the same time, microorganisms are involved in various industrial productions: this is genetic engineering, the production of antibiotics, enzymes, and others. proteins, artificial decomposition of waste (eg methane digestion of sewage), enrichment of metals. Some bacteria grow on substrates rich in petroleum products, and this serves as an indicator in the search and development of new deposits.