Bacteria are very small. The smallest known bacteria are only 0.2 micron long, so most of them can only be seen under a microscope. The largest bacteria in the world can be directly seen by naked eyes, and its size is 0.2-0.6 mm. This is a kind of bacteria called Namibian sulfite bacteria.
Bacteria are generally single-celled, with simple cell structure and lack of nuclei and membranous organelles, such as mitochondria and chloroplasts. Based on these characteristics, bacteria belong to prokaryotes. There is another organism in prokaryotes called archaea, which is a new category created by scientists according to evolutionary relationships.
For the sake of distinction, this creature is also called eubacteria. Archaea and eubacteria are different in living environment, nutrition and heredity. The shapes of bacteria are quite diverse, mainly spherical, rod-shaped and spiral.
Bacteria are widely distributed in soil and water, or try to coexist with other organisms. The human body also carries quite a lot of bacteria. It is estimated that the total number of bacterial cells in human body and epidermis is about ten times that of human body.
In addition, some species are distributed in extreme environments, such as hot springs and even radioactive waste. They are classified as extremophile, and one of the most famous species is marine Huanghua, which was discovered by scientists in an Italian submarine volcano. Even on the space shuttle.
However, there are so many kinds of bacteria that scientists have only studied a few of them and named them. Of all the doors in the field of bacteria, only about half can be cultivated in the laboratory.
Extended data dissemination:
The most important way of bacterial asexual reproduction is binary division. The cell wall of a bacterial cell divides horizontally to form two daughter cells, which can produce gene recombination.
A single cell will also undergo genetic variation in the following ways: mutation (the genetic code of the cell itself changes randomly), transformation (transferring unmodified DNA from one bacterium to another in solution and successfully integrating it into bacterial DNA or plasmid to make it have new characteristics), transfection (virus or bacterial DNA);
Or their DNA is transferred to another bacterium through phage), bacterial conjugation (the DNA of one bacterium is transferred to another bacterium through a special protein structure formed between two bacteria). Bacteria can obtain gene fragments in these ways and pass the recombinant genome to their offspring through division. Many bacteria contain heterologous DNA fragments.
When bacteria are in an environment rich in temperature, humidity, air and nutrition. They will multiply rapidly and increase exponentially, and can form aggregates visible to the naked eye, such as colonies.
Some bacteria can form spore structure, and spores can withstand extreme conditions such as high temperature, drought and strong radiation, which is beneficial for them to survive in harsh environment and maintain their own continuity.
Baidu Encyclopedia _ Bacteria