Bacteria ("stick" from ancient Greek) represent the kingdom (group) of non-nuclear (prokaryotic) microorganisms, unicellular, as a rule. Today, about ten thousand of their species are known and described. Scientists suggest that there are more than a million of them.
A bacterial cell may have a round, crimped, rod-shaped shape. In rare cases, cubic, tetrahedral, star-shaped, as well as O- or C-shaped forms are found. Appearance determines the abilities that a bacterial cell possesses. For example, depending on the form, microorganisms have one or another degree of mobility, the ability to attach to the surface, one way or another absorption of nutrient compounds.
A bacterial cell includes three mandatory structures: a cytoplasmic membrane, a ribosome, and a nucleoid.
From the membrane on the outside there are several layers. In particular, there is a mucous membrane, capsule, cell wall. In addition, from the outside, various surface structures develop: villi, flagella. The cytoplasm and membrane are combined into the concept of “protoplast”.
A bacterial cell with all its contents is limited from the external environment using a membrane. Inside, in a homogeneous fraction of the cytoplasm, are proteins, soluble RNA, substrates of metabolic reactions, various compounds. The rest contains various structural elements.
The bacterial cell does not contain nuclear membranes and any other intracytoplasmic membranes that are not derivatives of the cytoplasmic membrane. However, for some prokaryotes, local “protrusion” of the main membrane is characteristic. These "protrusions" - mesosomes - perform various functions and divide the bacterial cell into functionally different parts.
All the data necessary for life is contained in one DNA. The chromosome, which includes a bacterial cell, usually has the shape of a ring, covalently closed. At one point, DNA attaches to the membrane and is placed in a separate, but not separated from the cytoplasm, structure. This structure is called the nucleoid. When expanded, the bacterial chromosome has a length of more than a millimeter. It is usually presented in a single copy. In other words, prokaryotes are almost all haploid. However, under certain specific conditions, a bacterial cell may contain copies of its chromosome.
Of particular importance in the life of the bacteria is the cell wall. However, this structural element is not required. In the laboratory, some forms of prokaryotes were obtained in which the wall was absent in whole or in part. These bacteria could exist under normal conditions, but in some cases they lost the ability to divide. In nature, there is a group of prokaryotes that do not contain walls in their structure.
On the outer surface of the wall may be an amorphous layer - a capsule. The mucous layers are separated from the microorganism quite easily, they have no connection with the cell. Covers also have a thin structure, they are not amorphous.
The reproduction of bacteria of some forms is carried out by means of isometric, binary transverse division or budding. Different groups have different variants of division. So, for example, in cyanobacteria, reproduction occurs in a multiple way - several consecutive binary divisions. As a result, four to a thousand new microorganisms are formed. They have special mechanisms by which the genotype plasticity is provided, which is necessary for adaptation to a changing external environment and evolution.