Figure 4.

Biosensors can report on horizontal gene transfer (HGT) between cells. (A) Cells use HGT of antibiotic resistance genes (ARG) to improve their fitness. (B) In engineered systems, like wastewater treatment plants, biosensors can report on the effect of operating conditions on HGT rates and the diversity of bacteria that participate in conjugation. (C) HGT biosensors can couple the production of a visual reporter to HGT. With this approach, the donor cells keep the reporter production off, while the receiver cells are unable to repress reporter production. Cells acquiring a conjugative plasmid (cPlasmid) through HGT produce an output that can be quantified using flow cytometry. (D) Biosensors can record a HGT event by writing new sequences into their DNA (red), which can be read out using qPCR or sequencing at later times provided that the DNA remains extractable.