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Eco-friendly Bio-manufacturing of Flavonoid Dyes in Escherichia coli via Computer-mediated Optogenetic Regulation

Natural dyes are increasingly considered as an eco-friendly solution to the serious water pollution generated by the textile and dye industries. Traditional production of natural dyes from plants heavily exhausts land and labour. While bio-manufacturing is an attractive alternative, it remains costly and chemically-intensive. We aim to develop a new bio-manufacturing method of producing flavonoids in E. coli for use as natural dyes. To eliminate the use of expensive chemical inducers to switch from growth to production phase and allow dynamic gene regulation, we designed an optogenetic circuit using a blue light repressible promoter for flavonoid biosynthesis. As it is critical to monitor cellular metabolic burden for efficient production, we introduced a stress-sensing fluorescence reporter. To optimize operations, a computer-aided system was developed to regulate gene expression using light according to the feedback from the stress sensor. To demonstrate this approach, we produced Luteolin, a natural yellow dye.

The Problem

Water pollution is a key problem in the textile dyeing and dyestuff production industry. Drinking water flows out of our faucets in Singapore, which we sometimes take for granted. However, in many parts of the world, rivers and waterbodies that are sources of drinking water and livelihood are becoming heavily polluted by textile dyeing. Due to irresponsible disposal of industrial effluents, hard-to-biodegrade synthetic dyes by textiles and dyestuff producers and ineffective wastewater treatment, chemicals accumulate and make these rivers and waterbodies unsuitable for human consumption, and inhospitable for marine fauna and flora.

Already, Citarum River in Indonesia is a clear example of this murky problem. The 30 million residents relying on the river as their only water source and livelihood are experiencing adverse skin conditions and increased exposure to infectious diseases, while the river has almost no aquatic life left. In some areas of the river, lead levels at more than 1,000 times the USEPA standard in drinking water have been found. River water rapidly changing colours from red, to green, yellow, and black due to high concentrations of dye is not an uncommon sight. However, Citarum River is not an isolated case. Similar sights can be seen in China’s Pearl River, Buriganga River in Bangladesh and Bagmati River in India. In Bangladesh, Dhaka, 719 factories and textile mills generate close to 200 metric tons of wastewater per ton of fabric per year. On the global scale, the textile dyeing and dyestuff production industry is the second most pollutive industry, coming in only after oil, and also uses the most water apart from agriculture.

In recent years, some efforts have been put in place to revive natural dyes as a more sustainable alternative to synthetic dyes. However, this motion has not been gaining much traction, as traditional natural dye production faces many constraints. Natural dyes produced traditionally often have inconsistent quality, varying from batch to batch of plants used. Furthermore, it is land and labour intensive, and competes with food production for land use.

The Problem Statement

Our team believes that synthetic dyes are the unsustainable solution, and have taken the synthetic biology approach to natural dye bioproduction in the hopes of making natural dyes a stronger, better substitute to synthetic dyes. What this means is our dyes have to be non-toxic, have reduced use of chemicals in its production, environmentally friendly and appealing to fashion designers and consumers.