Figure 4.

The integrated furan aldehydes detoxification system. A furfural responsive promoter and multiple effector genes are integrated into the chromosome. In the absence of furan aldehydes, this artificial operon is inactive and effector genes are not expressed. Furan aldehydes activate the responsive promoter to drive the expression of effector genes. Effectors are produced to mitigate the toxicity of furan aldehydes. Example effectors shown in the graph are furfural reductase (A), anti-oxidative protein (B), polyamine transporter (C), and chaperonin (D), assuming these effectors have synergistic epistatic interaction. When furfural level decreases, promoter remains silenced and no more new effectors are made. This design provides a controllable mechanism for furfural tolerance to minimize metabolic burden and maximize the benefit of effector genes.