Noncanonical Peloruside A Biosynthesis by an Uncultivated Verrucomicrobiota Symbiont.
An unusually complex modular PKS pathway comprising nonelongating ketosynthases (KSs), two internal thioesterases (TEs), and an acetyl coenzyme A ligase that orchestrate O-acetylation/elimination, acetyl-CoA recycling, and configurational proof-reading to facilitate selective Z-double bond incorporation is revealed.