Nitromethanians are largely oxygen-intolerant microbes which produce methane and fix nitrogen. In addition to their ancestral methanogenesis, they also combine dissolved or atmospheric nitrogen and hydrogen to form ammonia, which they then use to form other organic compounds necessary to their survival. They typically live in low-oxygen environments, such as soil, mud, decaying flora, and the guts of many kinds of fauna. Although they must be in low-oxygen environments to function well, Nitromethanians are capable of surviving above ground for short periods of time, somewhat protected by their cell walls.
Nitromethanians generally range in shape from cylindrical to pill-shaped to spherical. Many have flattened forms, and those which live within the guts of fauna tend to be more streamlined with specialized flagella comparable in shape to those of the Ribbon-Tailed Detriti. Gut-dwelling variants are most commonly found in organisms which already use gut microbes, such as asterostrids and descendants of Vinagob, and their nitrogen-fixing ability benefits these gut ecosystems greatly. Like many Terran microbes, individual species are many in number and can be difficult to distinguish.