Continuous culture systems are essential for synthetic biology techniques like Directed Evolution (DE) and Phage-Assisted Continuous Evolution (PACE), which require metabolically active bacterial cultures for extended periods. Turbidostats, which maintain cell density using real-time optical density (OD) feedback, offer ideal conditions for inducing gene expression during mid-log phase, which is the optimal growth stage for synthetic circuit activity. However, current PACE-compatible bioreactors are either cost-prohibitive or require significant technical expertise. Here, we present the OptoPACE Bioreactor (OPB), a low-cost, user-friendly turbidostat system optimized for PACE and optogenetic control. The OPB uses a 650 nm laser and photoresistor to measure turbidity, an Arduino microcontroller for feedback control, and NeoPixel LEDs to enable multispectral optogenetic stimulation. Designed with 3D-printed components and off-the-shelf electronics, the system operates with a single peristaltic pump and uses the siphon effect to simplify fluidics. A custom motor control shield and an LCD-rotary encoder interface enable code-free operation. The OPB supports dual bioreactors connected unidirectionally, ensuring continuous culture while maintaining precise control over optical inputs and nutrient flow. The entire system can be built for under 200, significantly lowering the barrier to entry for labs interested in continuous evolution. By combining affordability, modularity, and ease of use, the OptoPACE Bioreactor provides a robust platform for protein engineering and synthetic biology, enabling broader adoption of advanced continuous evolution methods like PACE.
Crane et al. (Fri,) studied this question.
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