The design and engineering of biological systems — a field known as Synthetic Biology —has been heralded by many to be the defining technology of the 21st century. Just as electronics and computers have changed almost every facet of our day-to-day lives, the consequences of engineering microbes might also be as far reaching. Engineered bugs are already being developed to produce pharmaceuticals and fuels, monitor their environment, detect trace chemicals, degrade plastic waste, and perform computing operations.
Microbes, however, are considerably more complex — and hence less predictable — than electronic components. For this reason, one of the best strategies scientists have for engineering them is to use a brute force approach: try out as many different biodesigns as possible and see what works best.
Doing this with microbes is tricky. Designing and constructing a single engineered bacteria is labour intensive and can take weeks. To circumvent this, researchers have turned to cell-free systems: a collection of biomolecules that can reproduce biochemical features of interest, for example the synthesis of proteins from a genetic circuit. This greatly simplifies things as after all you are now merely handling what is essentially a sack of chemicals.
This is where it really gets interesting. As opposed to testing out different genetic circuits one-by-one in a test tube, Hori et al developed a microfluidic device which forms millions of droplets an hour – each droplet acts as a mini test tube, each containing a slightly different version of the circuit. The circuit was made up of three strands of DNA which interact with one another in a non-linear way to produce a Green Fluorescent Protein. The fact that it is non-linear means predicting how they interact is difficult and makes the tactic of trying out different combinations more appealing. Using microfluidics, the authors created a generic library by combining different ratios of these three components. By incubating the droplets and monitoring protein production levels, they were able to map out the parameter space to see which genetic circuit from their library worked best.
Although simply a proof-of-concept, this droplet microfluidic approach has shown to be incredibly powerful, and in addition to being used in genetic circuit design has the potential to rapidly explore large parameter spaces in other areas of chemistry and biology.
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Cell-free extract based optimization of biomolecular circuits with droplet microfluidics
Yutaka Hori, Chaitanya Kantak, Richard M. Murray and Adam R. Abate
Lab Chip, 2017
*Free to access until 8th September 2017.
Yuval Elani is an EPSRC Research Fellow in the Department of Chemistry at Imperial College London. His research involves using microfluidics in bottom-up synthetic biology for biomembrane construction, artificial cell assembly, and for exploring bionterfaces between living and synthetic microsystems.