Microbial Production of Natural Rainbow Colorants

Bacterial strains capable of producing three carotenoids and four violacein derivatives were developed, completing the seven colors in the rainbow spectrum. The integration of systems metabolic engineering and membrane engineering led to the production of rainbow colorants for the first time.

Article | Fall 2022

Colorants are widely used in many societies and are directly related to human health when we ingest food additives and wear cosmetics. However, most colorants are made from petroleum and can cause unexpected side effects and health problems. Furthermore, they raise environmental concerns given the water pollution that occurs from the dyeing of fabrics in the textiles industry. For these reasons, the demand for the production of natural colorants using microorganisms has increased, but this demand cannot readily be met due to the high cost and low yield of the necessary bioprocesses.

These challenges have inspired metabolic engineers at KAIST. The team, led by Distinguished Professor Sang Yup Lee, published a study entitled “Production of rainbow colorants by metabolically engineered Escherichia coli” as the journal cover in Advanced Science on July 7, 2021 http://doi.org/10.1002/advs.202100743

This research reports for the first time the production of rainbow colorants comprising three carotenoids and four violacein derivatives from glucose or glycerol via systems metabolic engineering and membrane engineering. The research group focused on the production of hydrophobic natural colorants useful for lipophilic foods and for the dyeing of garments. First, using systems metabolic engineering, which is an integrated technology to engineer the metabolism of a microorganism, the three carotenoids of astaxanthin (red), β-carotene (orange), and zeaxanthin (yellow) and the four violacein derivatives of proviolacein (green), prodeoxyviolacein (blue), violacein (navy), and deoxyviolacein (purple) could be produced. Thus, the production of natural colorants covering the complete rainbow spectrum was achieved.

When hydrophobic colorants are produced from microorganisms, the colorants accumulate inside the cell. As the accumulated capacity is limited, hydrophobic colorants cannot be produced with concentrations exceeding this limit. In this regard, the researchers engineered the cell morphology and generated inner-membrane vesicles (spherical membranous structures) to increase the intracellular capacity so as to allow greater accumulation of the natural colorants. To promote production further, the researchers generated outer-membrane vesicles to secrete the natural colorants, thus succeeding in efficiently producing all seven rainbow colorants. It was even more impressive that the production of natural green and navy colorants was achieved for the first time.

“The production of the seven natural rainbow colorants capable of replacing the current petroleum-based synthetic colorants was achieved for the first time,” explained Distinguished Professor Sang Yup Lee. He explained that another important point of the research is that the integrated metabolic engineering strategies developed from this study are generally applicable to the efficient production of other natural products useful as pharmaceuticals or nutraceuticals.

Dr. Dongsoo Yang and Dr. Seon Young Park from the Department of Chemical and Biomolecular Engineering participated in this study as the co-first authors. This study was supported by the Rural Development Administration, Republic of Korea (Project No. PJ01550602).