Directed evolution is a process based on darwinian principles which employs artificial selection to achieve optimality in an evolutionary system. This method is widely used both in experimental and industrial labs with the intention of optimizing a given property in a defined context (e.g. thermostability and specificity in case of enzymes). Despite its apparent power, directed evolution is not always tractable and it is usually labor-intensive. Here, the authors have employed a micro-fluidic chamber to construct an autonomous system capable of fast and efficient artificial evolution without any human supervision.
As schematically shown in the figure below, the authors aim to optimize an RNA enzyme capable attaching itself to the 3' end of any DNA fragment. To this end, they make DNA fragments with pre-designed T7 promoters; following incubation with reverse transcriptase and T7 polymerase enzymes the RNAs that have successfully attached themselves to the fragment can be amplified.
This set-up is not new, the novelty of this paper is in how they have implemented it. They have constructed a microfluidic chamber with computer-controlled valves that through automated monitoring can indefinitely repeat the above process. As shown in the figure taken from the original paper, this involves three steps: (1) mixing period for the reaction to happen (C); (2) isolation step in which a small volume of the sample is retained while the rest is washed away (B) and (3) incubation phase where the RT and T7pol are added to amplify RNA and restart the mixing period (A).
While mostly engineering in nature, this study reveals how these systems invented for other purposes can be employed to increase speed and accuracy in biological set-ups.
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