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Bacteria are among the fastest growing and most widespread organisms on Earth. They can thrive in nearly every environment or ecosystem, and some can double their population in only 10min [1]. Even though bacterial growth follows quite simple mathematical laws, many parameters of this process are far from being fully understood. This makes bacterial growth hard to control in a laboratory. Thus unraveling these genotypic and phenotypic processes represents an important challenge in current public health issues. We have developed a biological system that will enable researchers to control live cell density in a culture. Such a tool could be of great interest for improving our understanding of bacteria: characterizing oxidative stress defence and recovery, monitoring growth media component consumption rates, or just making sure the culture you left Friday evening in the lab is in the same state on Monday morning.
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.
Overview on Light Automated Cell Control.
Source: Carpentier et al., Structural Basis for the Phototoxicity of the Fluorescent Protein KillerRed, FEBS Letters,2009.
Our system utilizes Escherichia coli (E. coli) bacteria that produce the photosensitizing protein KillerRed. When illuminated with light, the fluorescent protein KillerRed (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 [3-4] was developed to regulate the concentration of this protein.
We have built a mathematical model based on the results given by our biological experiments, that can help predict the amount of living cells within our culture and their growth rate in a specific set of experimental conditions. These conditions depend on: light intensity, illumination time, and concentration of intracellular KillerRed protein. The model was further implemented on a, Arduino microcontroller, which drives our electronic system TalkE'Coli. This device, equipped with a white light source, a set of filters and a photodiode, can then be used to regulate living cell population and growth to any arbitrary level within natural limits.
[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.
[4] K.E. McGinness et al., Engineering Controllable Protein Degradation, Molecular Cell, June 2006.
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