Bifunctional enzyme that catalyzes the reactions from geranylgeranyl diphosphate to phytoene (phytoene synthase) and lycopene to beta-carotene via the intermediate gamma-carotene (lycopene cyclase). The cyclase preferentially catalyzes the symmetric cyclization of both ends of the substrate to produce dicyclic carotenoids. Beta-carotene is further processed to the acidic carotenoid astaxanthin. all-trans-lycopene = gamma-carotene gamma-carotene = all-trans-beta-carotene 2 (2E,6E,10E)-geranylgeranyl diphosphate = 15-cis-phytoene + 2 diphosphate Carotenoid biosynthesis; beta-carotene biosynthesis. Carotenoid biosynthesis; phytoene biosynthesis; all-trans-phytoene from geranylgeranyl diphosphate: step 1/1. Down-regulated in stationary phase. In the N-terminal section; belongs to the lycopene beta-cyclase family. In the C-terminal section; belongs to the phytoene/squalene synthase family.