Bacteria occur in various external forms, such as: spherical, cylindrical, helical, with stems, with attachments, and with several cells arranged.
The size of bacteria is very different. Apart from a few exceptions, individual bacterial cells cannot be seen with the naked eye.
Bacteria usually have a cell wall, all possess cytoplasm with Cytoplasmamembran and ribosomes. The gram coloration allows bacteria to be divided into two large groups, which differ in the structure of their cell walls. Gram-positive and gram-negative bacteria are differentiated. However, not all bacterial species can be classified by technology, so there are also gram variables and gram indefinite species.
The gram coloration is important for the diagnosis of infectious diseases. Gram-positive and Gram-negative bacteria can often only be combated with different antibiotics.
Gram-positive bacteria have one of the membrane-bearing thickness, multi-layer "Mureinhülle" consisting of Peptidoglycanen.
Examples of Gram-positive bacteria are all species of the tribal Firmicutes, such as the genera Streptococcus, Enterococcus, Staphylococcus, listeria, Bacillus, Clostridium and Lactobacillus.
Gram-negative bacteria, on the other hand, only have a thin, single-layer Mureinhülle. Examples of Gram-negative bacteria are all kinds of department Proteobacteria, according to the Enterobacteriaceae (Escherichia coli, Salmonella, Shigella, Klebsilla, Proteus, Entrobacter).
Representatives of other departments are, for example, Streptobacillus Moniliformis and Meningococcus.
The DNA of bacteria is freely present in the cytoplasm as a stranded molecule, a so-called bacterial chromosome. Some bacteria also have two bacterial chromosomes, for example Ralstonia eutropha strain H16.
In the cytoplasm, more DNA is often found in the form of smaller, also strand-shaped, self-contained molecules, the plasmids. These are duplicated independently of the bacterial chromosome and passed on to reproduction.
The genome of the gut bacterium Escherichia coli consists of almost 4.7 million base pairs, the sequence of which is fully known. The DNA molecule is about 1.4 millimeters long with a diameter of only 2 nanometers. It contains approximately 4400 genes.
The way of life and metabolism of the bacteria is very different. So there are bacteria that need oxygen (aerobic bacteria or aerobes), bacteria for the oxygen poison is (obligatory anaerobic bacteria or obligatory anaerobes), and bacteria that are tolerant to oxygen (optional anaerobes). Some bacteria are capable of photosynthesis (phototroph). Most bacteria, however, gain the energy for their metabolism from chemical reactions of substances that they absorb from the environment. They're chemotroph.
Most bacteria live together in nature in the form of biofilms.
The multiplication of the bacteria is asexual by cell division. All descendants of asexual propagation have an identical genome and therefore form a clone.
(Source: "Bacteria" Wikipedia.de)