Some endoliths have specialized in feeding on their autotroph relatives. Trophic mutualism often occurs between an autotroph and a heterotroph. "S. acidocaldarius" is a facultative autotroph. It is an autotroph that uses energy from sunlight. The rate of photosynthesis on the other hand, indicates the metabolic rate of an autotroph. The Greek term "autotroph" was coined by the German botanist Albert Bernhard Frank in 1892. "Trichodesmium thiebautii" is a simultaneous diazotroph and autotroph. Unlike some of its relatives, this species is an autotroph. Thus, "D. acuminata" is a mixotroph, primarily a heterotroph, but autotroph once it acquires plastids.