For decades engineers have dreamed of programming organisms to sustainably produce ethylene, a chemical that is nicknamed "the king of petrochemicals" for its importance in plastics. Now, one hopeful pathway to this petrochemical is nearing reality, via a photosynthetic bacterium that is genetically specialized to turn sunlight and carbon dioxide (CO2) into ethylene. But before industry can load up on tanks of living green liquid, researchers are first overcoming some metabolic barriers around ethylene production.