Living Material with Temperature-Dependent Light Absorption

Engineered living materials (ELMs) exhibit desirable characteristics of the living component, including growth and repair, and responsiveness to external stimuli. Escherichia coli (E. coli) are a promising constituent of ELMs because they are very tractable to genetic engineering, produce heterologous proteins readily, and grow exponentially. However, seasonal variation in ambient temperature presents a challenge in deploying ELMs outside of a laboratory environment because E. coli growth rate is impaired both below and above 37 degrees C. Here, a genetic circuit is developed that controls the expression of a light-absorptive chromophore in response to changes in temperature. It is demonstrated that at temperatures below 36 degrees C, the engineered E. coli increase in pigmentation, causing an increase in sample temperature and growth rate above non-pigmented counterparts in a model planar ELM. On the other hand, at above 36 degrees C, they decrease in pigmentation, protecting the growth compared to bacteria with temperature-independent high pigmentation. Integrating the temperature-responsive circuit into an ELM has the potential to improve living material performance by optimizing growth and protein production in the face of seasonal temperature changes. Escherichia coli (E. coli) are a promising constituent of engineered living materials (ELMs), but growth slows below and above 37 degrees C. E. coli is engineered to enable temperature-controlled expression of a light-absorptive chromophore in a model planar ELM. When grown below 36 degrees C, the cells produce pigment, absorbing light and increasing in temperature and growth rate above a non-pigmented strain. When grown above 36 degrees C, the ELM remains unpigmented, protecting growth compared to a strain with always-on pigmentation.image