In laboratories at KAIST in Daejeon, South Korea, Distinguished Professor Sang Yup Lee's team has engineered a microscopic revolution: they've taught bacteria to spin petrochemicals into thin air, replacing them with glycerol—the humble byproduct of making biodiesel. The discovery, published in the Proceedings of the National Academy of Sciences, means nylon, that workhorse plastic in everything from athletic wear to car parts, no longer has to come from fossil fuels.
Nylon's ubiquity masks an environmental burden. The plastic polymer, prized for its flexibility in clothing and films and its strength in automotive and machinery applications, has been synthesized almost entirely through petrochemical processes that leave a heavy carbon footprint. But nylon doesn't need to come from oil refineries. It needs three molecular building blocks: adipic acid, hexamethylenediamine, and epsilon-caprolactam. For the first time, a team of researchers has shown these can be produced directly from glycerol—a renewable waste product from biodiesel manufacturing—using nothing more exotic than modified strains of E. coli.
The breakthrough lies in how Lee's team organized the bacterial work. Rather than asking a single microbial strain to perform an impossible leap from glycerol to finished nylon components, they split the job into an upstream module and a downstream module, each handled by specially designed E. coli strains with different metabolic roles. The upstream strain produces adipic acid from glycerol; the downstream strains convert that intermediate into either hexamethylenediamine (for nylon 6,6) or epsilon-caprolactam (for nylon 6). The numbers in nylon's name refer to carbon atoms in the raw materials—a detail that matters far less than what the team achieved: producing all three precursors in a single integrated fermentation platform.
The path to those numbers required meticulous engineering. The team tested and optimized multiple enzymes—carboxylic acid reductases, transaminases, and custom-designed fusion proteins—identifying which combinations worked best. They used artificial intelligence to enhance performance of key enzymes in the upstream pathway. They devised a "delayed inoculation" strategy, introducing the second bacterial strain only after adequate adipic acid had accumulated, rather than adding both simultaneously. Each refinement nudged the yields higher.
The current production levels—6 grams per liter of adipic acid, 230 milligrams per liter of hexamethylenediamine, and 808 micrograms per liter of epsilon-caprolactam—don't yet rival petroleum-derived routes at scale. But the research team notes these represent world-class performance for direct production from glycerol, a baseline from which improvement becomes inevitable. As the team continues refining enzyme designs and metabolic engineering strategies, those numbers will climb.
What matters most is not today's yield, but tomorrow's possibility. A renewable carbon source—waste glycerol that would otherwise sit unused—can now become the foundation for materials woven into millions of lives. Lee's modular platform, designed from the outset to be expandable, points toward a future where petrochemical processes for nylon and other polymers become optional rather than inevitable. The bacteria have learned their lesson. Now humans must scale it.