The current work presented the first non-flexible eunicellane scaffold synthesizing enzyme, MicA, discovered by genome mining from bacteria. Through extensive mechanistic investigations, MicA was proven to synthesize an unusual eunicellane scaffold possessing a distinctive chirality combination of trans (C1 and C10)-cis (Δ 2,3 ) following catalytic route as coral-derived eunicellane synthase, diverging from the bacteria-derived Bnd4 or AlbS. These discoveries have enabled us to propose a principle that a "trans-cis" combination gives non-flexible eunicellane skeletons.