Biology of bacteria. Structure of a bacterial cell

The kingdom "Bacteria" consists of bacteria and blue-green algae, general characteristics which lies in the small size and absence of a nucleus separated by a membrane from the cytoplasm.

Who are bacteria

Translated from Greek “bakterion” means stick. For the most part, microbes are single-celled organisms invisible to the naked eye that reproduce by division.

Who discovered them

For the first time, a Dutch researcher who lived in the 17th century, Anthony Van Leeuwenhoek, was able to see the smallest single-celled organisms in a homemade microscope. Study the world around us through the magnifying glass of a magnifying glass he began while working in a haberdashery store.

Anthony Van Leeuwenhoek (1632 - 1723)

Leeuwenhoek subsequently focused on making lenses capable of magnification up to 300 times. In them, he examined the smallest microorganisms, describing the information received and transferring what he saw to paper.

In 1676, Leeuwenhoek discovered and presented information about microscopic creatures, to which he gave the name “animalcules.”

What do they eat?

The smallest microorganisms existed on Earth long before the appearance of humans. They have a ubiquitous distribution, feeding on organic food and inorganic substances.

By way of absorption nutrients Bacteria are usually divided into autotrophic and heterotrophic. For existence and development, heterotrophs use waste products from the organic decomposition of living organisms.

Representatives of bacteria

Biologists have identified about 2,500 groups of different bacteria.

According to their form they are divided into:

• cocci having spherical outlines;
• bacilli - rod-shaped;
• vibrios that have curves;
• spirilla – spiral shape;
• streptococci, consisting of chains;
• staphylococci that form grape-like clusters.

According to the degree of influence on the human body, prokaryotes can be divided into:

• useful;
• harmful.

Microbes dangerous to humans include staphylococci and streptococci, which cause purulent diseases.

The bacteria bifido and acidophilus are considered beneficial, stimulating the immune system and protecting the gastrointestinal tract.

How do real bacteria reproduce?

Reproduction of all types of prokaryotes occurs mainly by division, followed by growth to the original size. Having reached a certain size, an adult microorganism splits into two parts.

Less commonly, reproduction of similar unicellular organisms is performed by budding and conjugation. When budding on the mother microorganism, up to four new cells grow, followed by the death of the adult part.

Conjugation is considered the simplest sexual process in unicellular organisms. Most often, bacteria that live in animal organisms reproduce in this way.

Bacteria symbionts

Microorganisms involved in digestion in the human intestine are shining example bacteria symbionts. Symbiosis was first discovered by the Dutch microbiologist Martin Willem Beijerinck. In 1888, he proved the mutually beneficial close coexistence of unicellular and legume plants.

Living in the root system, symbionts, feeding on carbohydrates, supply the plant with atmospheric nitrogen. Thus, legumes increase fertility without depleting the soil.

There are many successful symbiotic examples involving bacteria and:

• person;
• algae;
• arthropods;
• sea ​​animals.

Microscopic single-celled organisms assist the systems of the human body and promote cleansing waste water, participate in the circulation of elements and work to achieve common goals.

Why are bacteria classified into a special kingdom?

These organisms are characterized by their small size, lack of a formed nucleus, and exceptional structure. Therefore, despite external resemblance, they cannot be classified as eukaryotes, which have a formed cell nucleus limited from the cytoplasm by a membrane.

Thanks to all their features, in the 20th century scientists identified them as a separate kingdom.

The most ancient bacteria

The smallest single-celled organisms are considered the first life to emerge on Earth. Researchers in 2016 discovered buried cyanobacteria in Greenland that were about 3.7 billion years old.

In Canada, traces of microorganisms that lived approximately 4 billion years ago in the ocean have been found.

Functions of bacteria

In biology, between living organisms and their environment, bacteria perform the following functions:

• processing of organic substances into minerals;
• nitrogen fixation.

In human life, single-celled microorganisms play an important role from the first minutes of birth. They provide a balanced intestinal microflora, influence the immune system, and maintain water-salt balance.

Bacterial reserve substance

In prokaryotes, reserve nutrients accumulate in the cytoplasm. Their accumulation occurs in favorable conditions, and is consumed during fasting.

Bacterial reserve substances include:

• polysaccharides;
• lipids;
• polypeptides;
• polyphosphates;
• sulfur deposits.

The main sign of bacteria

The function of the nucleus in prokaryotes is performed by the nucleoid.

Therefore, the main characteristic of bacteria is the concentration of hereditary material in one chromosome.

Why are representatives of the kingdom of bacteria classified as prokaryotes?

The absence of a formed nucleus was the reason for classifying bacteria as prokaryotic organisms.

How bacteria survive unfavorable conditions

Microscopic prokaryotes are capable of long time endure unfavorable conditions, turning into disputes. There is a loss of water from the cell, a significant decrease in volume and a change in shape.

Spores become insensitive to mechanical, temperature and chemical influences. In this way, the property of viability is preserved and effective resettlement is carried out.

Conclusion

Bacteria – oldest form life on Earth, known long before the appearance of man. They are present everywhere: in the surrounding air, water, in the surface layer earth's crust. Habitats include plants, animals and humans.

Active study of single-celled organisms began in the 19th century and continues to this day. These organisms are the main part everyday life people and have a direct impact on human existence.

Everyone knows that bacteria are the most ancient type of living creatures that inhabit our planet. The first bacteria were the most primitive, but as our earth changed, so did the bacteria. They are present everywhere, in water, on land, in the air we breathe, in food, in plants. Just like people, bacteria can be good and bad.

Beneficial bacteria are:

• Lactic acid or lactobacilli. One of these good bacteria is a lactic acid bacterium. This is a rod-shaped type of bacteria that lives in dairy and fermented milk products. These bacteria also inhabit the human oral cavity, intestines, and vagina. The main benefit of these bacteria is that they produce lactic acid as a fermentation, thanks to which we get yogurt, kefir, fermented baked milk from milk, in addition, these products are very useful for humans. In the intestines, they play the role of cleansing the intestinal environment from bad bacteria.
• Bifidobacteria. Bifidobacteria are found mainly in the gastrointestinal tract, just like lactic acid bacteria are capable of producing lactic acid and acetic acid, due to which these bacteria control the growth of pathogenic bacteria, thereby regulating the pH level in our intestines. Various varieties of bifidobacteria help get rid of constipation, diarrhea, and fungal infections.
• Escherichia coli. The human intestinal microflora consists of most microbes of the Escherichia coli group. They contribute good digestion, and also participate in some cellular processes. But some varieties of this stick can cause poisoning, diarrhea, and kidney failure.
• Streptomycetes. The habitat of streptomycetes is water, decomposing compounds, soil. Therefore, they are especially useful for the environment, because... Many processes of decomposition and combinations are carried out with them. In addition, some of these bacteria are used in the production of antibiotics and antifungal drugs.

Harmful bacteria are:

• Streptococci. Chain-shaped bacteria, which, when entering the body, are the causative agents of many diseases, such as tonsillitis, bronchitis, otitis media and others.
• Plague stick. A rod-shaped bacterium that lives in small rodents causes terrible diseases such as plague or pneumonia. It's a plague terrible disease, which can destroy entire countries, and is compared to biological weapons.
• Helicobacter pylori. The habitat of Helicobacter pylori is the human stomach, but in some people the presence of these bacteria causes gastritis and ulcers.
• Staphylococcus. The name staphylococcus comes from the fact that the cells resemble a bunch of grapes in shape. For humans, these bacteria cause severe diseases with intoxication and purulent formations. No matter how terrible bacteria are, humanity has learned to survive among them thanks to vaccination.

At this very moment, man, when you read these lines, you are benefiting from the work of bacteria. From the oxygen we breathe in to the nutrients our stomachs extract from food, we have bacteria to thank for thriving on this planet. In our body there are about ten times more microorganisms, including bacteria, than our own cells. Essentially, we are more microbes than people.

It's only recently that we've begun to understand a little about microscopic organisms and their impact on our planet and health, but history shows that centuries ago our ancestors were already harnessing the power of bacteria to ferment foods and drinks (whoever heard of bread and beer?).

In the 17th century, we began to study bacteria directly in our bodies in close connection with us - in the mouth. Antoni van Leeuwenhoek's curiosity led to the discovery of bacteria when he examined a plaque between his own teeth. Van Leeuwenhoek waxed poetic about the bacteria, describing the bacterial colony on his teeth as “a little white substance, like hardened dough.” Placing the sample under a microscope, van Leeuwenhoek saw that the microorganisms were moving. So they are alive!

You should know that bacteria played a vital role for the Earth, becoming key point in creating breathable air and biological richness for the planet we call home.

In this article, we will provide you with an overview of these tiny but very influential microorganisms. We'll look at the good, the bad, and the downright bizarre ways bacteria have shaped human history and environment. First, let's look at how bacteria differ from other types of life.

Bacteria Basics

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 a few microns (millionths of a meter) - and figure out how they relate to other life forms, plants, animals, viruses and fungi.

As you may know, cells are the building blocks of life, from the tissues of our body to the tree that grows outside our 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 unique work, helping the cell work.

Bacteria, however, do not have a nucleus, and their genetic material (DNA) floats freely inside the cell. These microscopic cells do not have organelles and have other methods of reproduction and transfer of genetic material. Bacteria are considered prokaryotic cells.

• Do bacteria survive in an environment with or without oxygen?
• Their shape: rods (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 cell interior?
• 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 cousins.

Bacteria-like prokaryotes, now classified as archaea, were once together with bacteria, but as scientists learned more about them, they gave bacteria and archaea their own categories.

Microbial nutrition (and miasma)

Like people, animals and plants, bacteria need food to survive.

Some bacteria - autotrophs - use basic resources such as sunlight, water and chemicals from the environment to create food (think of cyanobacteria, which have been converting sunlight into oxygen for 2.5 million years). Other bacteria are called heterotrophs by scientists because they get their energy from existing organic matter as food (for example, dead leaves on forest soil).

The truth is that what may be tasty to bacteria will be disgusting to us. They have evolved to absorb all types of products, from oil spills and nuclear byproducts to human waste and decomposition products.

But a bacteria's affinity for a particular food source could benefit society. For example, art experts from Italy turned to bacteria that can eat excess layers of salt and glue, reducing the durability of priceless works of art. Ability to recycle bacteria organic matter also very beneficial to the Earth, both in soil and water.

From daily experience, you are well aware of the odor caused by bacteria consuming the contents of your trash can, processing leftover food and emitting its own gaseous by-products. However, this is not all. You can also blame bacteria for causing those awkward moments when you pass gas yourself.

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 different surfaces- from rocks to the teeth of your mouth.

Biofilms have their pros and cons. On the one hand, they are mutually beneficial natural objects(mutualism). On the other hand, they can be a serious threat. For example, doctors who treat patients with medical implants and devices have serious concerns about biofilms because they provide real estate for bacteria. Once colonized, biofilms can produce byproducts that are toxic—and sometimes fatal—to humans.

Like people in cities, cells in a 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 conditions. When there is no more food and conditions become unbearable, bacteria preserve themselves by creating a hard shell, an endospore, which puts the cell into a state of dormancy and preserves the genetic material of the bacterium.

Scientists find bacteria in such time capsules that were stored for 100 or even 250 million years. This suggests that the bacteria can be stored independently for a long time.

Now that we know what opportunities colonies provide to bacteria, let's figure out how they get there - through division and reproduction.

Bacteria reproduction

How do bacteria create colonies? Like other life forms on Earth, bacteria need to replicate themselves in order to survive. Other organisms do this through sexual reproduction, but not bacteria. But first, let's discuss why diversity is good.

Life undergoes natural selection, or the selective forces of a certain environment allow one type to flourish and reproduce more than another. You may remember that genes are the machinery that instructs a 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 more genetic diversity there is, 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 DNA and passing it on to both parts of the divided cell.

Since the resulting cell will ultimately be identical to the one from which it was born, this method of propagation 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 exchange genetic material without reproduction. There are several ways that bacteria use to do this. One method involves collecting 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 a home. When viruses infect a new bacterium, they 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 sense stressful changes in the environment, such as food shortages or chemical changes.

Understanding how bacteria adapt is extremely important for combating them and creating antibiotics for medicine. Bacteria can exchange genetic material so frequently that sometimes treatments that worked before no longer work.

No high mountains, no great depths

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 any one time, but some estimates put their number (bacteria and archaea together) at 5 octillion - a number with 27 zeros.

Classifying bacterial species is extremely difficult for obvious reasons. There are now approximately 30,000 officially identified species, but the knowledge base is constantly growing, and there are opinions that we are just the tip of the iceberg of all types of bacteria.

The truth is that bacteria have been around for a very long time. They produced some of the oldest fossils, dating back 3.5 billion years. Scientific research suggests that cyanobacteria began creating oxygen approximately 2.3-2.5 billion years ago in the world's oceans, saturating the Earth's atmosphere with the oxygen we breathe to this day.

Bacteria can survive in the air, water, soil, ice, heat, on plants, in the intestines, on the skin - everywhere.

Some bacteria are extremophiles, meaning they can resist extreme conditions, when it is either very hot or cold, or there is a lack of nutrients and chemicals that we usually associate with life. Researchers have found such bacteria in Mariana Trench, the deepest point on Earth at the bottom Pacific Ocean, near hydrothermal vents in water and ice. There are also bacteria that like high temperatures, 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 dark side. Some bacteria can be pathogenic, meaning they cause illness and disease.

Throughout human history, certain bacteria have (understandably) gotten a bad rap, causing panic and hysteria. Take the plague, for example. The bacterium that causes the plague, Yersinia pestis, not only killed more than 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 resistance to antibiotics, bacteria that cause anthrax, pneumonia, meningitis, cholera, salmonellosis, tonsillitis and other diseases that still remain close to us always pose a danger to us.

This is especially true for Staphylococcus aureus, the bacterium responsible for staphylococcal infections. This “superbug” causes numerous problems in clinics, since patients very often contract this infection when implanting medical implants and catheters.

We've 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 may affect most of the bacterial population. But those bacteria that survive will develop resistance to the drug and remain, waiting for the next chance. Therefore, doctors recommend completing the course of antibiotics to the end, and in general using them as rarely as possible, only as a last resort.

Biological weapons are another frightening aspect of this conversation. Bacteria can be used as a weapon in some cases, notably anthrax was used at one time. In addition, not only people suffer from bacteria. A separate species, Halomonas titanicae, has shown an appetite for the sunken ocean liner Titanic, eating away at the metal of the historic ship.

Of course, bacteria can cause more than just harm.

Heroic bacteria

Let's explore good side bacteria. After all, these microbes gave us delicious foods like cheese, beer, sourdough and other fermented elements. They also improve human health and are used in medicine.

Individual bacteria can be thanked for the formation human evolution. Science is collecting more and more data about microflora - microorganisms that live in our bodies, especially in digestive system and intestines. Research shows that bacteria, new genetic materials, and the diversity they bring to our bodies allow humans to adapt to new food sources that have not been exploited before.

Let's look at it this 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 your food, especially carbohydrates. The more diverse the bacteria we consume, the more diversity our bodies gain.

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 human health, metabolism and susceptibility to allergens. Preliminary studies in mice have shown that metabolic diseases like obesity are associated with a diverse and healthy microbiota, rather than our prevailing “calories in, calories out” mentality.

The possibilities of introducing certain microbes and bacteria into the human body, which can provide certain benefits, are now being actively studied, but at the time of writing general recommendations on their use have not yet been established.

In addition, bacteria played an important role in the development of scientific thought and human medicine. Bacteria played a leading role in the development of Koch's 1884 postulates, which led to the general understanding that disease is caused by a specific type of microbe.

Researchers studying bacteria accidentally discovered penicillin, an antibiotic that saved many lives. Also, quite recently, in connection with this, it was opened easy way edit the genome of organisms, which could 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.

Jul 22, 2017 Gennady

Reproduction of bacteria by fission is the most common method of increasing the size of a microbial population. After division, bacteria grow to their original size, which requires certain substances (growth factors).

The methods of reproduction of bacteria are different, but most of their species have a form of asexual reproduction by fission. Bacteria rarely reproduce by budding. Sexual reproduction of bacteria is present in a primitive form.

Rice. 1. The photo shows a bacterial cell at the stage of division.

Genetic apparatus of bacteria

The genetic apparatus of bacteria is represented by a single DNA - chromosome. The DNA is closed in a circle. The chromosome is localized in a nucleotide that does not have a membrane. A bacterial cell contains plasmids.

Nucleoid

A nucleoid is an analogue of a nucleus. It is located in the center of the cell. It contains DNA, the carrier of hereditary information in a folded form. Unwound DNA reaches a length of 1 mm. The nuclear substance of a bacterial cell does not have a membrane, a nucleolus or a set of chromosomes, and does not divide by mitosis. Before dividing, the nucleotide is doubled. During division, the number of nucleotides increases to 4.

Rice. 2. The photo shows a bacterial cell in a section. A nucleotide is visible in the central part.

Plasmids

Plasmids are autonomous molecules folded into a ring of double-stranded DNA. Their mass is significantly less than the mass of a nucleotide. Despite the fact that plasmid DNA encodes hereditary information, they are not vital and necessary for the bacterial cell.

Rice. 3. The photo shows a bacterial plasmid.

Stages of division

After reaching a certain size characteristic of an adult cell, division mechanisms are launched.

DNA replication

DNA replication precedes cell division. Mesosomes (folds of the cytoplasmic membrane) hold DNA until the division (replication) process is completed.

DNA replication is carried out with the help of enzymes DNA polymerases. During replication hydrogen bonds In double-stranded DNA, DNA is broken, resulting in the formation of two daughter single-stranded DNA from one DNA. Subsequently, when the daughter DNAs took their place in the separated daughter cells, their restoration occurs.

As soon as DNA replication is complete, a constriction appears as a result of synthesis, dividing the cell in half. First, the nucleotide undergoes division, then the cytoplasm. Cell wall synthesis completes division.

Rice. 4. Scheme of bacterial cell division.

Exchange of DNA sections

In Bacillus subtilis, the process of DNA replication ends with the exchange of two DNA sections.

After cell division, a bridge is formed through which the DNA of one cell passes into another. Next, both DNAs are intertwined. Some sections of both DNA stick together. At the sites of adhesion, DNA segments are exchanged. One of the DNA goes along the jumper back into the first cell.

Rice. 5. Variant of DNA exchange in Bacillus subtilis.

Types of bacterial cell divisions

If cell division is ahead of the separation process, then multicellular rods and cocci are formed.

With synchronous cell division, two full-fledged daughter cells are formed.

If the nucleotide divides faster than the cell itself, then multinucleotide bacteria are formed.

Methods for separating bacteria

Division by breaking

Division by breaking is characteristic of anthrax bacilli. As a result of this division, the cells break at the junction points, breaking the cytoplasmic bridges. Then they repel each other, forming chains.

Sliding division

With sliding separation, after division the cell becomes detached and, as it were, slides along the surface of another cell. This method separation is characteristic of some forms of Escherichia.

Split split

With secant division, one of the divided cells with its free end describes an arc of a circle, the center of which is the point of its contact with another cell, forming a Roman quinque or cuneiform (Corynebacterium diphtheria, Listeria).

Rice. 6. The photo shows rod-shaped bacteria forming chains (anthrax bacilli).

Rice. 7. The photo shows a sliding method for separating E. coli.

Rice. 8. The splitting method of separating corynebacteria.

Type of bacterial clusters after division

Clusters of dividing cells have a variety of shapes, which depend on the direction of the division plane.

Globular bacteria arranged one by one, two by two (diplococci), in packets, in chains, or like bunches of grapes. Rod-shaped bacteria - in chains.

Spiral shaped bacteria- chaotic.

Rice. 9. The photo shows micrococci. They are round, smooth, and white, yellow and red in color. In nature, micrococci are ubiquitous. They live in different cavities of the human body.

Rice. 10. In the photo there are diplococcus bacteria - Streptococcus pneumoniae.

Rice. 11. The photo shows Sarcina bacteria. Coccoid bacteria cluster together in packets.

Rice. 12. The photo shows streptococcus bacteria (from the Greek “streptos” - chain). Arranged in chains. They are causative agents of a number of diseases.

Rice. 13. In the photo, the bacteria are “golden” staphylococci. Arranged like “bunches of grapes”. The clusters are golden in color. They are causative agents of a number of diseases.

Rice. 14. In the photo, the coiled Leptospira bacteria are the causative agents of many diseases.

Rice. 15. The photo shows rod-shaped bacteria of the genus Vibrio.

Bacterial division rate

The rate of bacterial division is extremely high. On average, one bacterial cell divides every 20 minutes. Within just one day, one cell forms 72 generations of offspring. Mycobacterium tuberculosis divides slowly. The entire division process takes them about 14 hours.

Rice. 16. The photo shows the process of streptococcus cell division.

Sexual reproduction of bacteria

In 1946, scientists discovered sexual reproduction in a primitive form. In this case, gametes (male and female reproductive cells) are not formed, but some cells exchange genetic material ( genetic recombination).

Gene transfer occurs as a result conjugation- unidirectional transfer of parts genetic information in the form plasmids upon contact of bacterial cells.

Plasmids are small DNA molecules. They are not associated with the chromosome genome and are capable of doubling autonomously. Plasmids contain genes that increase the resistance of bacterial cells to unfavorable conditions external environment. Bacteria often pass these genes on to each other. Transfer of genetic information to bacteria of another species is also noted.

In the absence of a true sexual process, it is conjugation that plays a huge role in the exchange of useful characteristics. This is how the ability of bacteria to exhibit drug resistance is transmitted. The transfer of antibiotic resistance between disease-causing populations is particularly dangerous for humanity.

Rice. 17. The photo shows the moment of conjugation of two E. coli.

Phases of bacterial population development

When inoculated on a nutrient medium, the development of the bacterial population goes through several phases.

Initial phase

The initial phase is the period from the moment of sowing to their growth. On average, the initial phase lasts 1 - 2 hours.

Breeding delay phase

This is the phase of intensive bacterial growth. Its duration is about 2 hours. It depends on the age of the crop, the period of adaptation, the quality of the nutrient medium, etc.

Logarithmic phase

During this phase, there is a peak in the rate of reproduction and increase in the bacterial population. Its duration is 5 - 6 hours.

Negative acceleration phase

During this phase, there is a decline in the reproduction rate, the number of dividing bacteria decreases, and the number of dead bacteria increases. The reason for the negative acceleration is the depletion of the nutrient medium. Its duration is about 2 hours.

Stationary maximum phase

During the stationary phase, an equal number of dead and newly formed individuals is noted. Its duration is about 2 hours.

Death Acceleration Phase

During this phase, the number of dead cells progressively increases. Its duration is about 3 hours.

Logarithmic death phase

During this phase, bacterial cells die at a constant rate. Its duration is about 5 hours.

Decrease rate phase

During this phase, the remaining living bacterial cells enter a dormant state.

Rice. 18. The figure shows the growth curve of a bacterial population.

Rice. 19. In the photo, a colony of Pseudomonas aeruginosa is blue-green, a colony of micrococci yellow, Bacterium prodigiosum colonies are blood red in color and Bacteroides niger colonies are black in color.

Rice. 20. The photo shows a colony of bacteria. Each colony is the offspring of a single cell. In a colony, the number of cells is in the millions. The colony grows in 1 - 3 days.

Division of magnetically sensitive bacteria

In the 1970s, bacteria living in the seas were discovered that had a sense of magnetism. Magnetism allows this amazing creatures navigate the lines magnetic field Earth and find sulfur, oxygen and other substances it needs so much. Their “compass” is represented by magnetosomes, which consist of a magnet. When dividing, magnetically sensitive bacteria divide their compass. In this case, the constriction during division becomes clearly insufficient, so the bacterial cell bends and makes a sharp fracture.

Rice. 21. The photo shows the moment of division of a magnetically sensitive bacterium.

Bacterial growth

When a bacterial cell begins to divide, two DNA molecules move to opposite ends of the cell. Next, the cell is divided into two equal parts, which are separated from each other and increase to their original size. The division speed of many bacteria averages 20 - 30 minutes. Within just one day, one cell forms 72 generations of offspring.

During the process of growth and development, a mass of cells quickly absorbs nutrients from the environment. This is facilitated by favorable environmental factors - temperature regime, a sufficient amount of nutrients, the required pH of the environment. Aerobic cells require oxygen. It is dangerous for anaerobes. However, unlimited proliferation of bacteria does not occur in nature. Sunlight, dry air, lack of food, high temperature environmental and other factors have a detrimental effect on the bacterial cell.

Rice. 22. The photo shows the moment of cell division.

Growth factors

For the growth of bacteria, certain substances (growth factors) are necessary, some of which are synthesized by the cell itself, some of which come from the environment. The need for growth factors is different for all bacteria.

The need for growth factors is a constant feature, which makes it possible to use it for identifying bacteria, preparing nutrient media, and using it in biotechnology.

Bacterial growth factors (bacterial vitamins) - chemical elements, most of which are water-soluble B vitamins. This group also includes hemin, choline, purine and pyrimidine bases and other amino acids. In the absence of growth factors, bacteriostasis occurs.

Bacteria use growth factors to minimum quantities and unchanged. A number of chemicals in this group are part of cellular enzymes.

Rice. 23. The photo shows the moment of division of a rod-shaped bacterium.

The most important bacterial growth factors

• Vitamin B1 (thiamine). Takes part in carbohydrate metabolism.
• Vitamin B2" (riboflavin). Takes part in redox reactions.
• Pantothenic acid is integral part coenzyme A.
• Vitamin B6 (pyridoxine). Takes part in amino acid metabolism.
• Vitamins B12(cobalamins are substances containing cobalt). Accept active participation in the synthesis of nucleotides.
• Folic acid. Some of its derivatives are part of enzymes that catalyze the synthesis of purine and pyrimidine bases, as well as some amino acids.
• Biotin. Participates in nitrogen metabolism and also catalyzes the synthesis of unsaturated fatty acids.
• Vitamin PP(nicotinic acid). Participates in redox reactions, the formation of enzymes and the metabolism of lipids and carbohydrates.
• Vitamin H(para-aminobenzoic acid). It is a growth factor for many bacteria, including those inhabiting the human intestines. Folic acid is synthesized from para-aminobenzoic acid.
• Hemin. It is a component of some enzymes that take part in oxidation reactions.
• Kholin. Takes part in the reactions of cell wall lipid synthesis. It is a supplier of methyl group in the synthesis of amino acids.
• Purine and pyrimidine bases(adenine, guanine, xanthine, hypoxanthine, cytosine, thymine and uracil). The substances are needed mainly as components of nucleic acids.
• Amino acids. These substances are components of cell proteins.

Requirement for growth factors of certain bacteria

Auxotrophs To ensure life, they require the supply of chemicals from the outside. For example, clostridia are not able to synthesize lecithin and tyrosine. Staphylococci require the supply of lecithin and arginine. Streptococci require the supply of fatty acids - components of phospholipids. Corynebacteria and Shigella require nicotinic acid. Staphylococcus aureus, pneumococci and Brucella require vitamin B1. Streptococci and tetanus bacilli - in pantothenic acid.

Prototrophs independently synthesize the necessary substances.

Rice. 24. Different conditions environmental conditions have different effects on the growth of bacterial colonies. On the left is steady growth in the form of a slowly expanding circle. Right - rapid growth in the form of "escapes".

Studying the need of bacteria for growth factors allows scientists to obtain a large microbial mass, so necessary in the manufacture of antimicrobial drugs, serums and vaccines.

Read more about bacteria in the articles:

Bacterial proliferation is a mechanism for increasing the number of microbial populations. Bacterial division is the main method of reproduction. After dividing, the bacteria must reach adult size. Bacteria grow by rapidly absorbing nutrients from their environment. Growth requires certain substances (growth factors), some of which are synthesized by the bacterial cell itself, and some of which come from the environment.

There are a huge number of bacteria in our world. Among them there are good ones, and there are also bad ones. Some we know better, others worse. In our article we have selected a list of the most famous bacteria living among us and in our body. The article is written with a bit of humor, so don’t judge strictly.

Provides “face control” in your insides

Lactobacilli (Lactobacillus plantarum) living in digestive tract people since prehistoric times have been doing a great and important job. Like garlic they scare away vampires pathogenic bacteria, preventing them from settling in your stomach and causing intestines to become upset. Welcome! Pickled cucumbers and tomatoes, sauerkraut will strengthen the strength of bouncers, but know that hard training and stress from physical activity reducing their ranks. Add some blackcurrants to your protein shake. These berries reduce fitness stress due to the antioxidants they contain.

2. BELLY DEFENDER Helicobacter pylori

Stops hunger pangs at 3 pm

Another bacteria that lives in the digestive tract, Helicobacter pylori, develops in your childhood and helps maintain a healthy weight throughout your life by controlling the hormones responsible for hunger! Eat 1 apple every day.

These fruits produce lactic acid in the stomach, in which most harmful bacteria cannot survive, but which Helicobacter pylori loves. However, keep H. pylori in check, they can go against you and cause stomach ulcers. Make scrambled eggs with spinach for breakfast: the nitrates from these green leaves thicken the walls of the stomach, protecting it from excess lactic acid.

3. Pseudomonas aeruginosa

Loves showers, hot baths and pools

Living in warm water The bacterium Pseudomonas aeruginosa enters the scalp through the pores of the hair follicles, causing an infection accompanied by itching and pain in the affected areas.

Don't want to wear a swim cap every time you take a bath? Fend off the carder's invasion with a chicken or salmon sandwich and eggs. Large quantity follicles need protein to be healthy and effectively fight foreign bodies. Don't forget about fatty acids, which are absolutely essential for a healthy scalp. 4 cans of canned tuna or 4 medium avocados per week will help you with this. No more.

4. Harmful bacteria Corynebacterium minutissimum

High-tech protozoa

Harmful bacteria can lurk in the most unexpected places. For example, Corynebacterium minutissimum, which causes a rash, loves to live on the touchscreens of phones and tablet computers. Destroy them!

It's strange, but no one has developed it yet free application, fighting these microbes. But many companies produce cases for phones and tablets with antibacterial coating, which is guaranteed to stop the growth of bacteria. And try not to rub your hands together when drying them after washing - this can reduce the bacteria population by 37%.

5. THE NOBLE RASSAL Escherichia coli

Good bad bacteria

The bacterium Escherichia coli is thought to be the cause of tens of thousands of infectious diseases annually. But it only gives us problems when it finds a way to leave the colon and mutate into a disease-causing strain. Normally, it is quite useful for life and provides the body with vitamin K, which maintains healthy arteries, preventing heart attacks.

To keep this headline-grabbing bacteria at bay, include legumes in your diet five times a week. The fiber in the beans is not broken down but moves into the colon where E. coli can feast on it and continue its normal reproduction cycle. Black beans are the richest in fiber, then Idelim, or moon-shaped, and only then the usual red beans. Legumes not only keep bacteria under control, but their fiber also limits your afternoon cravings and increases the body's ability to absorb nutrients.

6. BURNING Staphylococcusaureus

Eats away the youth of your skin

Most often, boils and pimples are caused by the bacterium Staphylococcusaureus, which lives on the skin of most people. Acne is, of course, unpleasant, but, having penetrated through damaged skin into the body, this bacterium can cause more serious diseases: pneumonia and meningitis.

The natural antibiotic dermicidin, which is toxic to these bacteria, is found in human sweat. Include high-intensity exercises in your workout at least once a week, trying to work at 85% of your maximum capacity. And always use a clean towel.

7. MICROB – GLUTTER Bifidobacterium animalis

® Lives in fermented milk products

The bacteria Bifidobacterium animalis inhabits the contents of jars of yogurt, bottles of kefir, curdled milk, fermented baked milk and other similar products. They reduce the time it takes for food to pass through the colon by 21%. Food does not stagnate, excess gases do not form - you are less likely to experience a problem code-named “Feast of the Spirit”.

Feed the bacteria, for example, with a banana - eat it after lunch. And for lunch itself, pasta with artichokes and garlic will be perfect. All these products are rich in fructo-oligo-saccharides - Bifidobacterium animalis loves this type of carbohydrates and eats them with pleasure, after which it reproduces with no less pleasure. And as the population grows, your chances of normal digestion increase.

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