Light Automated Cell Control (Lac²)

This year, the Grenoble-EMSE-LSU iGEM team has developed a bioelectronic device enabling the population control of a bacterial culture with light: Talk’E. Coli.

In general, bacteria are among the fastest growing and most widespread organisms on Earth. They can thrive in nearly every environment or ecosystem, and some can even reach a doubling time of only 10min [1]. Even though bacterial growth conforms to quite simple mathematical laws, many parameters of this process are far from being fully understood. Unraveling these genotypic and phenotypic processes represents an important challenge in current public health issues. Conceptually, we have developed a biological system that will enable researchers to monitor and control cellular growth with light. Such an undertaking could be of great interest for improving the understanding of bacterial functions, especially in regards to characterizing cellular populations and the defense mechanisms involved with oxidative stress responses.

Light allows for precise machine-to-cell and cell-to-machine communication in both time and space and was thus elected to interface a biological cell culture to our electronic device.
Our system utilizes Escherichia coli (E. coli) bacteria that are producing the photosensitizing protein KillerRed (KR). When illuminated with light, the KR fluorescent protein (580/630nm) produces Reactive Oxygen Species (ROS). These species irreversibly damage cell proteins, membranes, and DNA, ultimately leading to cell death [2]. Bacterial growth is monitored by measuring the fluorescence of cells containing KillerRed, and population control can be achieved by modulating the amount of ROS produced inside the bacteria with light stimulation. Since the amount of ROS produced is closely related to the amount of intracellular KillerRed, a photosensitive system [3] was developed to regulate the concentration of this protein.

The results given by our current biological experiments have enabled us to build a mathematical model that can help predict the amount of living cells within our culture and their growth rate in a specific set of experimental conditions such as: light intensity, illumination time, and concentration of intracellular KillerRed protein. The model was further implemented on a microcontroller, directing our electronic system Talk’E. Coli. This device, equipped with different light sources and a photodiode, can then be used to regulate cell population and growth to any arbitrary level within natural limits.

References:
[1] L. Elsgaard and D. Prieur, Hydrothermal vents in Lake Tanganyika harbor spore-forming thermophiles with extremely rapid growth, Journal of Great Lakes Research, March 2011.
[2] M.E. Bulina et al., A genetically encoded photosensitizer, Nature Biotechnology, January 2006.
[3] J.J. Tabor et al., Multichromatic Control of Gene Expression in Escherichia coli, Journal of Molecular Biology, 2011.