Figure 1. Creation of engineered dependency on Pt/HPt.

(a) Concept for the biocontainment strategy using engineered dependency on Pt/HPt. Under laboratory conditions, microbial growth is maintained by using any P source, including Pt and HPt. Common microbial strains are able to grow both inside and outside of laboratory facilities by using Pi or organic Pi compounds as P sources. A Pt/HPt-dependent strain, which can utilize Pt or HPt but not Pi, is not able to grow unless Pt/HPt is provided as a P source under laboratory conditions. This Pt/HPt-dependent strain is not able to grow in the environment because Pt and HPt are ecologically rare and not available in amounts sufficient to support bacterial growth. (b) Schematic of the engineered P metabolic pathway for biocontainment. Dependency on Pt or HPt is created by disruption of endogenous Pi and organic Pi transporters and exogenous expression of HtxBCDE and PtxD. HtxBCDE takes up Pt/HPt but not Pi or organic Pi compounds. PtxD and HtxA expression confer Pt- and HPt-oxidation activities, respectively.