Bacterial Genetics

(such as oxygen) in oxidation-reduction reactions or “redox” reactions, releasing energy that drives metabolic processes.

Those chemotrophic organisms or “chemotrophs” will use inorganic compounds or organic compounds as electron sources. Those using inorganic compounds (such as ammonia, hydrogen, or carbon monoxide) are called lithotrophs, while those that use organic compounds as electron sources are called organotrophs. Organisms can be aerobic, using oxygen as a terminal electron receptor, or anaerobic, using carbon dioxide, sulfate, and nitrate as terminal electron receptors. There are also heterotrophs, which get carbon from other forms of organic carbon, autotrophs, which fix carbon dioxide in order to have carbon for cell structures, and methanotrophs, which uses methane gas as a source for electrons and to gain carbon for metabolic processes.

BACTERIAL GENETICS

As mentioned, most bacteria have one circular chromosome, which can be very small (160,000 base pairs) or very large (12 million base pairs). There are a few bacterial types (such as Borrelia and Streptomyces) that have a single linear chromosome and even fewer that have more than one chromosome. Many bacteria have plasmids, which are extra-chromosomal DNA molecules that do things like confer antibiotic resistance, enhance metabolism, and create virulence factors for the bacterial species that contain them.

The bacterial genome can code for just a few hundred proteins or a couple of thousand genes. These organisms will have introns (non-coding DNA stretches) but not nearly as many as are seen in eukaryotic organisms. The daughter cell inherits an exact copy of the parent cell because of the way these cells divide. Evolution, however, can occur because of mutations in the DNA during cell division or because of genetic recombination.

As mentioned, there can be exchange of genetic material between cells. This can actually occur in three different ways: 1) Bacteria can take up DNA from the environment, particularly in environmentally stressful conditions. This is called transformation. 2) There can be an infection with bacteriophages in which foreign DNA