Traditionally, most bioproduction culture systems use just one strain of yeast or bacteria. Sometimes, though, you just need a little help from your friends.
That’s the idea behind the emerging field of synthetic ecology, which just achieved a major proof-of-principle success thanks to a team of MIT scientists. Cocultures have been used in specific cases before, but this was the first demonstration that a synthetic ecology can solve more general problems in biomanufacturing.
The team found a way to efficiently and effectively create the key biochemical intermediate cis-cis-muconic acid (MA), an important compound used for making numerous high-demand, bulk chemicals, with a yield of 4.7 g/L and 0.35 g/g from a glucose/xylose mixture, by far the highest ever reported.
To accomplish this feat, the team designed, optimized, and scaled-up a plug-and-play E. coli-E.coli coculture system that overcomes many limitations of single-strain biosynthetic culture systems. Typical monocultures are hampered by the difficulty of coaxing all pathway enzymes to play well together within a single cell, reduced efficiency due to metabolic stress, and secretion of pathway intermediates, which interferes with substrate utilization. In the coculture approach, an upstream cell produces and secretes a key intermediate, which a second downstream cell imports and finishes processing.
Using this approach, Zhang and colleagues found that:
- Production of MA achieved a yield of 0.35 g/g from a glucose/xylose mixture.
- The coculture system exhibits high capacity for accommodating variable sugar mixtures and efficiently converts them to MA.
- By mixing the same upstream cell with a different downstream producer, the system could also produce 4-hydroxybenzoic acid (4HB), another important industrial aromatic compound.
The independence of constituent cells of the coculture system makes it possible to engineer downstream cells without negative metabolic impacts on the upstream cell. As the team concludes, “these results confirmed that an E.coli–E.coli coculture system can be stably scaled up to use sugar mixtures efficiently”.
Explore the technical details of this breakthrough at PNAS, July 2015.