Generic term for any single-celled, microscopic (usually 0.5 to 5 microns, although can be smaller or larger) prokaryote carbon-based biological organisms. They may be spherical, rod shaped, spiral, even (on some worlds) amoeboid.
Bacteria do not have to be terragen. Naturally occurring bacterial lifeforms have been found on most life-bearing Eugaian, Euvenusian, and Eoarean worlds.
Although bacteria differ greatly in metabolism and chemistry, they share the basic functions of decomposers, autotrophs, and symbiotes. Because of their simplicity, rapid reproduction rate, and the ease with which their genetic material can be modified, many kingdoms of bacteria are frequently used for bionano templates and modifications. The term bacterioids is generally given to exotic-chemistry equivalents.