Our system degrades the herbicide chlorimuron-ethyl residues and secretes indole-3-acetic acid (IAA) to promote seed germination, which not only helps crops grow better but also increases yield. As the yield increases, more crop straw is produced in the fields. If the straw is discarded directly, it not only wastes valuable resources but may also cause environmental problems.

Figure 1: Communication with Squirrel-Beijing-I

When reviewing previous iGEM projects, we discovered the inspiring idea of the Squirrel-Beijing-I team, who once utilized engineered E. coli to degrade waste paper cellulose. Motivated by their approach, we contacted their team leader, Jessie Xiang, and discussed potential collaboration directions with her through WeChat and Tencent Meeting.

We plan to incorporate crop straw into a sustainable circular system. By utilizing the cellulose contained in the straw, we can achieve its conversion through a plant cellulose hydrolysis system:

Figure 2: Gene circuit of a plant cellulose hydrolysis system

• The cex gene and cen gene encode exoglucanase and endoglucanase (1,4-β-D-glucan hydrolase), respectively, which work synergistically to break down cellulose into galactose.
• Subsequently, the cep94A gene, encoding galactose phosphorylase, converts galactose into glucose.
• These glucose molecules serve as an energy source for the engineered E. coli, thereby supporting its growth and functional performance.

Figure 3: A closed-loop system of our program

Our project is no longer a simple “degradation–growth promotion” process, but has evolved into a closed-loop system of “herbicide degradation → crop yield increase → straw recycling → nutrient feedback to engineered bacteria.”