The genus Salinispora constitutes a discrete group of actinomycete bacteria thriving in oceanic sediments. In recent years, members of this genus have emerged as a new resource for natural products. The polycyclic sporolides are one example of the rich metabolome of these marine-dwelling microbes. Their unpredented framework which is composed of a chlorinated cyclopenta[a]indene ring and a highly oxidized cyclohexenone moiety raised questions about the biosynthesis of these compounds. Sequencing of the sporolide-producing S. tropica strain and subsequent gene inactivation experiments revealed an iterative type-I polyketide synthase to catalyze the formation of an enediyne intermediate which is cycloaromatized in a Bergmann-type reaction to the cyclopenta[a]indene ring. The origin of the cyclohexenone residue, however, remained unclear. We envisioned a multitude of biosynthetic scenarios via polyketide and shikimate origins to yield this highly functionalized building block, which we confirmed in vivo originates from tyrosine and two methionine-derived methyl groups. To decipher the pathway to the cyclohexenone moiety in more detail, we focused on the gene spoT1 within the sporolide biosynthetic gene cluster. Heterologous expression and biochemical characterization identified SpoT1 as a Fe(II)-dioxygenase that converts p-hydroxyphenylpyruvate into p-hydroxymandelate, thereby illuminating the initial biochemical reaction to the cyclohexenone unit.