Project Overview

As the standard of living improves dramatically, diabetes and obesity have largely changed our lives. Although different kinds of 0-cal food and drinks with sugar substitutes are produced, their taste is poor and their safety is yet to be verified. Nature has enlightened us with its solution: D-psicose, a very rare sugar. It is not only extremely low in energy but it also offers other benefits to health. As nature was not generous enough this time. The XJTU iGEM team has managed to harness the power of evolution to speed up the process.

DTE, or D-tagatose 3-epimerase, is the key in manufacturing D-psicose from D-fructose. The conversion rate of wild type enzyme is poor with value of less than 10%. We designed a DEcose (Directed Evolved D-psicose) platform to literally build a self-evolving factory for the DTE enzyme, where DE (Directed Evolution) provides us an automatic, high-throughput, repeatable production mode. The bacteria evolve with the evolving workflow, and produce a DTE enzyme with significantly high-activity. We also designed a series of devices to demonstrate the platform: the screening, selecting and coupling circuit.

Specifically, the screening circuit is to test the D-psicose productivity by converting it to the expression level of fluorescence reporter gene. The selecting circuit is to find suitable evolution pressure for selection of the concentration of antibiotics. The coupling circuit uses the tunable hairpin cassette to regulate the screening and the survival advantages, which provides solution for the problem that antibiotic resistance gene is excessively expressed in our system. All these circuits are combined to form a biosensor-based platform for evolving and selecting DTE, contributing to the improvement of productivity of D-psicose.

Will this directed evolution really work? Will it end up with higher conversion rate and yield? The modeling part clears up the doubts by “Production and Conversion Rate Simulink Model” which shows that within 1000 times of directed evolution, the conversion rate can be increased up to 10%.

In our integrated Human Practice, we conducted interviews with the public, including the patients, the experts, and the companies, as well as investigations on the market and cost of D-psicose. It reveals the importance and the urgency of our project, along with a lot of suggestions on improvements. We believe our project will offer benefits to the public and society.

Concluding, we provide a framework of directed evolution. It incubates the enzyme for the manufacturing of the nature’s precious gift: D-psicose.


[1] Klil-Drori A J, Azoulay L, Pollak M N. Cancer, obesity, diabetes, and antidiabetic drugs: is the fog clearing?[J]. Nature reviews Clinical oncology, 2017, 14(2): 85.

[2] Sun Y, Hayakawa S, Ogawa M, et al. Influence of a rare sugar, D-psicose, on the physicochemical and functional properties of an aerated food system containing egg albumen[J]. Journal of agricultural and food chemistry, 2008, 56(12): 4789-4796.

[3] Li C, Lin J, Guo Q, et al. D‐Psicose 3‐epimerase secretory overexpression, immobilization, and d‐psicose biotransformation, separation and crystallization[J]. Journal of Chemical Technology & Biotechnology, 2018, 93(2): 350-357.

[4] Arnold F H. Directed evolution: bringing new chemistry to life[J]. Angewandte Chemie International Edition, 2018, 57(16): 4143-4148.

[5] Rennig M, Martinez V, Mirzadeh K, et al. TARSyn: tunable antibiotic resistance devices enabling bacterial synthetic evolution and protein production[J]. ACS synthetic biology, 2018, 7(2): 432-442.