The most common reproduction in bacteria is asexual per bipartition or cissiparity. Bacterial DNA duplication occurs and further division into two cells. Bacteria multiply by this process very quickly when they have favorable conditions (doubles in 20 minutes).
The separation of the sister chromosomes has the participation of the mesosomes, internal folds of the plasma membrane in which there are also the participating enzymes of most cellular respiration.
Note that there is no formation of the division spindle nor of classical and typical figures of mitosis. Soon, it's not mitosis.
Some species of bacteria give rise, under certain environmental conditions, to resistant structures called spores. The spore-producing cell dehydrates, forms a thick wall, and its metabolic activity becomes greatly reduced. Certain spores are able to remain dormant for tens of years. Finding a suitable environment, the spore rehydrates and gives rise to an active bacteria, which reproduces by binary division.
The spores are very heat resistant and generally do not die when exposed to boiling water. This is why laboratories, which need to work under absolute aseptic conditions, usually use a special process called autoclaving, to sterilize liquids and utensils. The sterilization device, the autoclave, uses water vapor at temperatures around 120ºC, under a pressure that is twice the atmospheric pressure. After 1 hour in these conditions, even the most resistant spores die.
The canning industry takes strict measures in food sterilization to eliminate bacterial spores Clostridium botulinum. This bacterium produces botulism, an often fatal infection.
For bacteria, sexual reproduction means any process of transferring DNA fragments from one cell to another. Once transferred, the donor bacteria's DNA recombines with that of the recipient, producing chromosomes with new gene mixtures. These recombinant chromosomes will be transmitted to daughter cells when the bacteria divides.
DNA transfer from one bacterium to another can occur in three ways: for transformation, transduction and by conjugation.
In transformation, the bacteria absorb DNA molecules dispersed in the medium and are incorporated into the chromatin. This DNA may come, for example, from dead bacteria. This process occurs spontaneously in nature.
Scientists have used transformation as a technique for Genetic engineering, to introduce genes of different species into bacterial cells.
In transduction, DNA molecules are transferred from one bacterium to another using viruses as vectors (bacteriophages). These, when assembled within the bacteria, may eventually include pieces of DNA from the host bacteria. By infecting another bacterium, the virus that carries the bacterial DNA transfers it along with yours. If the bacterium survives viral infection, it may include the genes of another bacterium in its genome.
In bacterial conjugation, pieces of DNA pass directly from a donor bacterium, the "male", to a recipient, the "female". This happens through microscopic protein tubes called pili, which the male bacteria have on their surface.
The transferred DNA fragment recombines with the "female" bacterium chromosome, producing new genetic mixtures that will be transmitted to daughter cells in the next cell division.
Bacterial conjugation showing sexual pili.