Figure 6. Conceptual circuit for a therapeutic bacterium that colonizes a niche in the human microbiome and delivers a drug.

This circuit demonstrates how the different classes of regulators and circuits described in this review could be combined into a single system. The leftmost panel shows genetically modified bacteria that have colonized the interior of a human gastrointestinal tract. The upper right panel focuses on the conceptual circuit that the bacteria use to regulate their growth and deliver drugs to the human patient. An analog circuit¹⁰³ (left) and irreversible recombinases (right) are highlighted in the insets to emphasize the diverse biochemistries used to build this circuit.