Aromatic chemicals, such as flavonoids and alkaloids, are widely used in the industry as flavors, fragrances, pigments, food additives, nutraceuticals, and pharmaceuticals.
They are naturally occurring in plants, but there are many disadvantages with extraction of the chemicals from their native plant sources. Among other things they accumulate at low levels and purification requires separation from a multiple of other compounds of similar structure. This is an inefficient and expensive process. Also, chemical synthesis of these complex molecules is not considered commercially feasible. Microbial production of these products, in so called cell factories, is therefore an alternative.
"An outstanding challange"
“It is regarded as a safe, cost-competitive and scalable approach. However, microbial production of these aromatic amino acid (AAA)-derived products remains an outstanding challenge. This is because heterologous pathways, as opposed to native metabolism, always suffer from having low efficiency, by-product competition, and insufficient precursor supply, which all hinder the construction of robust cell factories,” says Yun Chen, Senior Researcher, at the Department of Biology and Biological Engineering at Chalmers University of Technology.
Optimising yeast as cell factories
Yun Chen and Post Doc Quanli Liu have recently published research results in the scientific publication Nature Communications. There they present their work optimising Saccharomyces cerevisiae (baking yeast) as cell factories for large scale production of flavonoids and alkaloids. The big advantage of using baking yeast is that it is frequently used in science as a model organism. There is a lot of research done on its metabolism, and it could provide similar eukaryotic cell environment for optimal expression of plant enzymes.
“For example, the cytochrome P450 oxidases that are key catalysts in most, if not all, of these plant-based biosynthetic pathways, are enzymes that are often anchored in the endoplasmic reticulum membrane. They are inherently difficult to functionally express in prokaryotic microorganisms, such as bacteria, that lack these organelles,” says Quanli Liu.
Increase the flux through bottlenecks
One of the bottlenecks for biosynthesis of aromatic compounds is the AAA biosynthetic pathway. The flux through the AAA biosynthesis is highly regulated, and thus these amino acids are normally much less abundant than other amino acids.
“Through systematical engineering and the aid of synthetic biology tools we have significantly enhanced the flux through the AAA biosynthetic pathway,” says Yun Chen.
The flux has been increased more than double, reaching a productivity more than 100 mg per liter per hour without fermentation optimization. This is already quite close to the criteria of industrial relevance in terms cost-efficiency for production of many these compounds.
Significant step for industrial biomanufacturing
With this established platform, the researchers can easily plug in many different plant pathways for production of different flavonoids and alkaloids. Further optimization may well be required, as the metabolism needs to be fine-tuned to maximize the yield and productivity for each different product.
“However, this work represents a significant step for industrial biomanufacturing of these important aromatic compounds, making it more achievable,” says Quanli Liu.
Text: Susanne Nilsson Lindh
Photo: Martina Butorac