E. coli bacteria engineered to produce Rhododendron drug compounds at viable scale

Plants produce an enormous variety of compounds with pharmacological potential, but producing those compounds at scale for drug development is a persistent challenge. Extracting them directly from plants is often expensive, environmentally problematic, and yields vary seasonally. Synthesizing them chemically is frequently impossible due to their molecular complexity. And previous attempts to produce them using microorganisms have consistently hit a wall of insufficient yield.

A team at Kobe University has now broken through that wall for a class of compounds derived from Rhododendron plants. Using engineered Escherichia coli bacteria, the researchers achieved production of 202 milligrams of orsellinic acid per liter - 40 times higher than the best previously reported microbial yield - and for the first time in the widely used bacterium E. coli. The findings were published in Metabolic Engineering.

Why these compounds matter

Rhododendron species produce a group of compounds called orsellinic acid-derived meroterpenoids, which have shown anticancer, anti-HIV, antidiabetic, and anti-inflammatory activities in laboratory studies. Orsellinic acid is the core precursor from which this entire class is biosynthesized. Getting reliable quantities of it is the first step toward any serious pharmacological evaluation or clinical development of these compounds.

Without a scalable production method, compounds remain trapped in early literature - promising in papers but impractical to develop. Doctoral student Tomita Itsuki, who led much of the experimental work, put the problem clearly: "There are many examples where compounds appear promising in the literature but fail to advance sufficiently in evaluation or applied research due to supply issues. I began to feel this is less an issue with individual compounds and more a structural challenge facing natural products research as a whole."

How the engineering worked

The team, led by bioengineer Hasunuma Tomohisa, used a combination of genetic and metabolic engineering strategies. They introduced genes from plants, fungi, and bacteria into E. coli, creating a hybrid biosynthetic pathway capable of producing orsellinic acid from the bacterium's standard metabolic inputs. They then analyzed the organism's metabolism in detail and optimized culture conditions - the temperature, nutrient availability, and growth phase - to maximize yield.

Achieving a complete eukaryotic biosynthetic pathway in a prokaryotic bacterium like E. coli is technically difficult because many plant enzymes require cellular compartments that E. coli lacks. The 202 mg/L result is described by the authors as a significant achievement partly because previous researchers considered this reconstruction difficult to execute in this bacterial host.

Beyond the core compound

In a second step, the team introduced a gene from Rhododendron itself to extend the pathway to grifolic acid - a specific meroterpenoid compound with potent anticancer and analgesic properties that serves as a representative target for the broader compound class. E. coli expressing this extended pathway did produce grifolic acid, confirming the concept. However, grifolic acid yields were low, and the team acknowledges that optimization is needed before this represents a viable production route for that specific compound. They have already identified metabolic bottlenecks to address in future work.

A platform, not just a product

The broader significance of the work lies in its platform nature. The same design strategy and metabolic engineering toolkit can in principle be adapted to produce other members of the meroterpenoid family and their derivatives. Hasunuma framed the ambition explicitly: "In the short term, the platform established in this study can be immediately applied to the production and evaluation of related compounds and their derivatives. However, the rational design strategy employed here serves as a foundational technology for the production of various complex compounds using E. coli."

The research was funded by the Japan Society for the Promotion of Science and the Japan Science and Technology Agency, and was conducted in collaboration with researchers from the University of Minho and the RIKEN Center for Sustainable Resource Science.