Favorable conditions for the growth of bacteria. General characteristics of bacteria. Structure, reproduction, nutrition

The division of bacterial cells is called “binary,” during which the duplicated nucleoids are associated with the plasma membrane and diverge due to the stretching of the membrane between the nucleoids, and then a constriction or septa is formed, dividing the cell in two. The nucleoid is a cyclic giant (1.6 mm) DNA molecule that forms numerous loop domains in a state of supercoiling.

The time between bacterial cell divisions averages 20-30 minutes. During this time, nucleoid DNA replication, segregation, separation of sister nucleoids and their further divergence, formation of a septum and cytotomy occur, dividing the original cell exactly in half.

It turned out that in bacterial cells, at the beginning of DNA synthesis, which begins with replication, both growing DNA molecules are associated with the plasma membrane (Fig. 330). In parallel with DNA synthesis, despiralization of loop domains occurs due to the work of a number of enzymes (topoisomerase, gyrase, ligase, etc.), which leads to the physical separation of two daughter (or sister) nucleoid chromosomes, which are still in close contact with each other. After such segregation of nucleoids, they diverge from the center of the cell, the place of their former location, by a quarter of the length of the cell in two opposite directions. As a result, two nucleoids are located in the cell. What is the mechanism of this discrepancy is as follows.

It was established that several groups of special proteins take part in the process of nucleoid divergence. One of them, Muk B, is a giant protein (mol. mass about 180 kDa, length 60 nm), consisting of a central helical section and terminal globular sections, reminiscent in structure of filamentous proteins of eukaryotes (myosin II chain, kinesin). At the N-terminus, Muk B binds to GTP and ATP, and at the C-terminus, to a DNA molecule. On this basis, the Muk B protein is considered a motor protein involved in nucleoid segregation.

In addition to the Muk B protein, bundles of fibrils containing the Caf A protein, which can bind to myosin heavy chains, like actin, participate in the divergence of nucleoids (Fig. 331).

The formation of a constriction, or septum, resembles the cytotomy of animal cells. Fibrillar thermosensitive proteins (Fts family) take part in the formation of septa. This is a group of several proteins, among which the FtsZ protein is the most studied. It is similar in most bacteria, archibacteria, and is found in mycoplasmas and chloroplasts. It is a globular protein similar in its amino acid sequence to tubulin. During cell division, all this protein is localized in the septum zone and forms a contractile ring reminiscent of actomyosin during animal cell division (Fig. 332).

In parallel with the formation of the septum, the murein layer of the bacterial cell wall grows due to the work of the polyenzymatic complex PBP-3, which synthesizes peptidoglycans.

Thus, during the division of bacterial cells, processes similar to the division of eukaryotes are observed: the divergence of chromosomes (nucleoids) due to the interaction of motor and fibrillar proteins, the formation of a constriction due to fibrillar proteins forming a contractile ring. Unlike eukaryotes, bacteria take part in these processes by completely different proteins.

Bacteria are prokaryotes(non-nuclear) cellular organisms.These are the simplest, smallest andwidespread organismsthat have existed on earth for more than 3billion years, but at the same time constantly
developing. Bacteria are sodifferent from other living thingsorganisms that they are classified into a separate kingdom, Bacteria. It's not like that all over the worldthere are many places devoid of bacteria. They live in water, soil, air,inside and on the surface of animal bodies and plants.

Shapes of bacteria

cocci (spherical) - solitary

diplococci (collected in twos)

tetracocci (four each)

chains (streptococci)

in the form of a bunch (staphylococci)

bacilli (rod-shaped)

convoluted - vibrios (comma-shaped)

spirilla (one or more regular curls)

spirochetes (long and thin convoluted shapes with numerous small whorls)

Vital activity of bacteria:

Breath

Aerobes - oxygen is necessary for life

Anaerobes - do not need oxygen to live

Many bacteria can glow when they breathe (glow of sea water, forest rot)

According to the method of nutrition they are divided into:

a) sporophytes - bacteria that feed on ready-made organic substances of dead organisms (lactic acid bacteria, putrefaction bacteria);

c) symbionts - live inside other organisms and benefit them. (nitrogen-fixing bacteria on the roots of legumes, intestinal bacteria)

d) autotrophic bacteria - capable of synthesizing organic substances from inorganic ones (photosynthetic - green bacteria and chemosynthetics - sulfur bacteria, nitrifying bacteria, iron bacteria, hydrogen bacteria, etc.)

Reproduction

Most bacteria reproduce by dividing the cell into 2 parts (amitosis) through constriction or as a result of the formation of a dividing septum. Cylindrical shapes are divided across, spherical - in any direction. Some reproduce by budding. The sexual process is noted only in a few cases (in E. coli). Bacteria are characterized by a high reproduction rate: division occurs quickly (after 20-30 minutes). With such intensity, the offspring of one bacterium would fill the basins of all seas and oceans in 5 days. However, their reproduction is limited by climatic conditions, the action sunlight, struggle between species, accumulation of metabolic products, etc.

Sporulation

Under unfavorable conditions, rod-shaped bacteria are capable of forming spores. Sporulation is not reproduction, because One spore is formed from each cell and the number of individuals does not increase.The spore develops inside the bacterial cell: up to 60% of the water becomes bound, the protoplast contracts and becomes covered with a very dense shell. The shell of the former cell is destroyed and the spore is released. It is able to remain viable for many years (resistant to drying, high and low temperatures, toxic substances). When favorable conditions occur, the spores swell, the membranes rupture and young formed cells come out. Thus, the spore (in bacteria) is the stage of experiencing unfavorable conditions

Bibliography.

1. M.V. Gusev, L.A. Minaeva. Microbiology. Textbook for special universities M.: "Academy", 2003

2. V.V. Lysak. Microbiology. Tutorial for medical universities. Minsk: BSU, 2007

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The main way bacteria reproduce is by dividing the cell in two (binary fission). In this case, the plasma membrane and the wall are invaginated and laced in half. Membrane invagination occurs between the attachment points of two daughter circular DNA molecules, resulting in daughter cells being provided with copies of the mother chromosome. Bacteria have the ability to form endospores. Some endospores have dense multilayer shells, are resistant to aggressive environmental factors and retain the ability to germinate for a long time.

The sexual process in bacteria involves the transfer of DNA from one cell to another, followed by genetic recombination. Exchange hereditary material can occur by conjugation (direct contact of cells), transduction (transfer of DNA by a bacteriophage virus) or transformation (absorption of DNA fragments from the outside). However, mutations are a universal source of variability. In combination with the rate of bacterial reproduction, they provide these organisms with a high ability to adapt to environmental conditions.

Various types of bacteria can use almost any organic compound as an energy source - not only nutrients such as sugars, amino acids and fats, but also excretory products such as urea and uric acid contained in urine and substances found in excrement. One type of bacteria can even use penicillin as a nutrient substrate, which kills many bacteria.