Light Automated Cell Control (Lac²)

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

When it comes to speed of growth, bacteria could be considered as the fastest organism on Earth. They are indeed able to grow in a wide set of environments, with a doubling time that can be as short as 10 min in optimal conditions [1]. Even though bacterial growth obeys quite simple mathematical laws, the series of very well coordinated operation of processes involved in this phenomenon are far from being fully understood. Unraveling these genotypic and phenotypic processes represents nowadays an important challenge in public health. Contextually, we have developed a biological system enabling to monitor and control cell growth with light. It could be of great interest for improving our understanding of bacterial functions, and particularly of the defense mechanisms involved in response to oxidative stress.

Light allows for precise machine-to-cell and cell-to-machine communication in both time and space and was thus elected as an interface between a biological cell culture and our electronic device.
Our system involves Escherichia Coli (E. coli) bacteria, producing the photosensitizing protein KillerRed. Upon light irradiation, this fluorescent protein (580/630 nm) produces Reactive Oxygen Species (ROS) which irreversibly damage cell proteins, membranes and DNA, leading to cell death [2]. Bacterial growth is here followed by monitoring the KillerRed-expressing cell red fluorescence and can be controlled by modulating the amount of ROS produced inside the bacteria, using white light stimulations. Since the amount of ROS produced, and thus the cytotoxicity, is closely related to the concentration in intracellular KillerRed, a photosensitive expression system enabling to control this protein level inside the cell was also developed.

The results given by the biological experiments has enabled us to build a mathematical model that can help predicting the amount of living cells within our culture and their growth rate, in a specific set of experimental conditions (light intensity, illumination time, concentration in intracellular KillerRed protein). This model was further implemented on a microcontroller, driving our electronic system Talk’E. Coli. This device, equipped with different light sources and a photodiode, can then be used for regulating 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.