Researchers shown four strains of E. coli bacteria working together can convert sugar into natural red anthocyanin pigment found in strawberries. The study opens the door to economical natural colors for industrial applications.
The research marks the first biosynthesis method using four strains of bacteria to manufacture a compound in a single step, said, Mattheos Koffas, a professor of chemical and biological engineering at Rensselaer.
Manufacturers increasingly interested in natural colors, a shift founded in research documenting the health hazards of artificial colors for foods and cosmetics. Natural pigments found in plants such as anthocyanins, carotenoids, or lycopene produce indisputably safe colors.
Anthocyanins producing all colors except green and are responsible for natural color found in foods like blueberries, raspberries, black rice.
But, producing anthocyanins for industrial use is challenging. Plant-derived pigments require costly processing and produce inconsistent results, because anthocyanin molecules are complex, chemists have been unable to synthesize them.
Koffas’ lab has been investigating a production method of anthocyanins involving genetic engineering since 2005. Sixteen genes govern the production of anthocyanin in plants. But, transferring those genes, and the molecular pathway trigger, from a plant to bacteria is not a straightforward process, said J. Andrew Jones, first author of the study. To adapt the molecular pathway from a plant to the bacteria, researchers pieced together genes from bacteria, yeast, and six different varieties of plants.
In early research, researchers introduced the entire molecular pathway it had assembled into a single strain of E.coli bacteria.
The current research divides the entire pathway among four different strains of bacteria, modified to assemble anthocyanin in stages. Researchers divided the pathway into “modules” that produced intermediates that easily diffuse out of the bacterial cell.
When combined in a single flask, the first bacteria ingest sugar and produce “intermediate” compounds, phenylpropanoic acids. While ingested second bacteria, produce a second intermediate, and forth until fourth strain produces anthocyanin.
In further research, researchers will optimize each stage of the process. Each of the four strains chosen based on its ability to produce its assigned intermediate. However, some segments produce more than others and the final output is modest, producing milligrams per liter of anthocyanin. Production will have to approach of hundreds of milligrams per liter to be a commercially viable approach.
More information: [mBio]