Requires Mg2+ for activity. H-1si of farnesyl diphosphate is lost in the formation of (1E,4S,5E,7R)-germacra-1(10),5-dien-11-ol. Formation of (-)-germacrene D involves a stereospecific 1,3-hydride shift of H-1si of farnesyl diphosphate. Both products are formed from a common intermediate . Other enzymes produce germacrene D as the sole product using a different mechanism. The enzyme mediates a key step in the biosynthesis of geosmin (see EC 18.104.22.168 geosmin synthase), a widely occurring metabolite of many streptomycetes, bacteria and fungi . Also catalyses the reaction of EC 22.214.171.124, (-)-germacrene D synthase.