Self-regulating 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 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, we develop a genetically-encoded mechanism for autonomous temperature homeostasis in ELMs containing E. coli by engineering circuits that control the expression of a light-absorptive chromophore in response to changes in temperature. We demonstrate that below 36{degrees}C, our 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, above 36{degrees}C, they decrease in pigmentation, protecting their growth compared to bacteria with temperature-independent high pigmentation. Integrating our temperature homeostasis 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.