Engineered living materials (ELMs) retain desirable characteristics of the living component, such as exponential growth, self-repair, and responsiveness to external stimuli. Escherichia coli are a promising constituent of ELMs because they are very tractable to genetic engineering.

Variation in ambient temperature presents a challenge in deploying ELMs outside of a laboratory environment. E. coli experience maximal growth near 37°C. In addition, E. coli protein synthesis decreases below 37°C, while protein misfolding and aggregation tends to increase with temperature.

Here, we develop a genetically encoded mechanism for autonomous temperature homeostasis in ELMs containing E. coli by engineering circuits that change expression of a light-absorptive chromophore in response to changes in temperature. Our simulations show that by increasing absorptivity below 36°C, the material will heat above the ambient temperature to preserve optimal growth and protein expression, and thus material functionality.

We program bacteria to respond to temperature using temperature-sensitive transcriptional repressors (TSRs). Two families of TSRs with switching temperatures ranging from 36°C to 44°C have been developed in our lab by directed evolution of TcI, a temperature-sensitive mutant of bacteriophage λ repressor cI, and TlpA, a transcriptional auto-repressor from the virulence plasmid of Salmonella typhimurium. These thermal bioswitches can be further tuned for optimal switching in the ELM application.

Formation of a black chromophore from a pale yellow precursor is enzymatically catalyzed. Integrating the gene for this enzyme into a genetic circuit with a down-shifted mutant of TlpA enables E. coli to express black chromophore at low temperatures and not at high temperatures.

We measure the ability of patches of E. coli (simulating an E. coli-based ELM) to grow in a custom lighted incubator at different ambient temperatures by observing patch diameter and thickness. We continuously monitor E. coli temperature under illumination using thermal IR imaging with custom controller software. Comparison of experimental results and simulations will be presented. We demonstrate thermal control of pigmentation and resulting increase in sample temperature.

Engineered living materials (ELMs) retain desirable characteristics of the living component, such as exponential growth, self-repair, and responsiveness to external stimuli. _Escherichia coli_ are a promising constituent of ELMs because they are very tractable to genetic engineering.

Variation in ambient temperature presents a challenge in deploying ELMs outside of a laboratory environment. _E. coli_ experience maximal growth near 37°C. In addition, _E. coli_ protein synthesis decreases below 37°C, while protein misfolding and aggregation tends to increase with temperature.

Here, we develop a genetically encoded mechanism for autonomous temperature homeostasis in ELMs containing _E. coli_ by engineering circuits that change expression of a light-absorptive chromophore in response to changes in temperature. Our simulations show that by increasing absorptivity below 36°C, the material will heat above the ambient temperature to preserve optimal growth and protein expression, and thus material functionality.

We program bacteria to respond to temperature using temperature-sensitive transcriptional repressors (TSRs). Two families of TSRs with switching temperatures ranging from 36°C to 44°C have been developed in our lab by directed evolution of TcI, a temperature-sensitive mutant of bacteriophage λ repressor cI, and TlpA, a transcriptional auto-repressor from the virulence plasmid of _Salmonella typhimurium._ These thermal bioswitches can be further tuned for optimal switching in the ELM application.

Formation of a black chromophore from a pale yellow precursor is enzymatically catalyzed. Integrating the gene for this enzyme into a genetic circuit with a down-shifted mutant of TlpA enables _E. coli_ to express black chromophore at low temperatures and not at high temperatures.

We measure the ability of patches of _E. coli_ (simulating an _E. coli_-based ELM) to grow in a custom lighted incubator at different ambient temperatures by observing patch diameter and thickness. We continuously monitor _E. coli_ temperature under illumination using thermal IR imaging with custom controller software. Comparison of experimental results and simulations will be presented. We demonstrate thermal control of pigmentation and resulting increase in sample temperature.

Toward a thermally self-regulating living material

ACS Fall 2021

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