From about the end of the 19th century, scientists began to accumulate knowledge about the differences between pro- and eukaryotic cells and thus gradually distinguished a separate kingdom of microorganisms, united by the lack of differentiation of cells - Protista. However, what bacteria are, at that moment they only had to study: only in the XX century. this knowledge was systematized.
Bacteria are found in all environments where organic matter can accumulate. They tolerate high and low temperatures, salinity and acidity. So, the kingdom of bacteria lives not only in the environment where they decompose organics for their life, but also densely populates many mucous membranes of animals and humans, helping to digest food and competing with
pathogenic microorganisms. Their role in nitrogen metabolism is especially great, since only cyanobacteria can process atmospheric nitrogen. However, some
bacteria are causative agents of diseases: plague, anaerobic and intestinal infections, syphilis, cholera and
anthrax.Morphology
The ultrastructure of bacteria can only be seen with an electron microscope, however, what bacteria are and how they look from the outside can be discerned by immersion microscopy using special staining methods. The sizes of these microorganisms vary from 0.1 to 10 Ξm, but the morphology of bacteria allows us to divide them into 3 main groups: spherical - cocci (mono-, diplo-, tetra-, streptococci and sarcinomas), rod-shaped - bacilli (mono-, diplo- , strepto-) and crimped - vibrios, spirillos and spirochetes. In laboratory conditions, to determine the type and enzymatic properties, they are grown on simple or special nutrient media by the formation of colonies, and in different environments they have different growth patterns.
Structure
In general, what bacteria are, their ultrastructure determines. Outside, bacteria are protected by a cell wall consisting of layers of peptidoglycan, lipids and teichoic acids. The concentration of the first determines the ability of bacteria to stain according to the Gram method in a smear, according to which they are classified into Gr + and Gr-. Some of them have an additional protective structure - a capsule containing K-antigen and preventing their phagocytosis inside the macroorganism, the action of toxic and mechanical factors. To learn more about what bacteria are, you need to study their intracellular structure: bacteria are filled with a cytoplasm in which other organelles (ribosomes, chromatophores) and nutrients (lipids, sugars) are dissolved. They, like all prokaryotes, do not have a formed nucleus, and all genetic information is stored in a double-stranded nucleic acid molecule located in the nucleoid zone and fixed to the membrane at one point. Outside of her genetic information is enclosed in plasmids, which can determine the development of pathogenic properties and factors. For movement, they use flagella and spirillas fixed in the cell by the basal body, and their reproduction occurs by dividing in two.