Kharaa

Kharaa is a virulent interstellar microbe which destroys genetic information. Humanity has encountered two strains, though the first encounter was only publicly admitted after the second.

—Attacks and destroys genetic information, even artificial molecules like foldamers and hachimoji —Spreads by spores on interstellar bodies, or attached to starships —Can infect all life on a planet, destroying sea and soil microbes and compromising the biosphere —Name derived from 'kharaal', a Mongolian word for curse

The first contacted strain of kharaa, the "green" strain, was encountered on the planet 4546b by survivors of crashed starships. In a coincidence so improbable that it has been seized on by religious revivals and conspiracy theorists, this strain could be treated by an enzyme produced by a species native to 4546b. (One popular theory, derived from survivors of Mongolian clan-corps, suggests that ancient aliens brought the kharaa to 4546b specifically to research the enzyme's effectiveness.)

The "orange" or "Sanji" strain of kharaa shares a common ancestor with the green strain, but it spreads through free space in spores or seeds. Once anchored in a viable environment, it grows mats of biological infestation and spawns monstrous organisms that defend and spread the bacterium. These organisms may be species previously infected by the bacteria and archived in a kind of genetic almanac.

Though the bacterial form of the orange strain can be resisted by nanotech, the larger forms are resistant and must be physically destroyed, generally by the weapons of TSF Frontiersmen.

Humanity is now at war with an invasive alien ecosystem.