Design of a New Biosensor for Algal H2 Production Based on the H2-Sensing System of Rhodobacter capsulatus

The H₂-sensing system of Rhodobacter capsulatus was engineered to elicit a fluorescent response upon cell exposure to H₂. The system is surprisingly sensitive to H₂ and is capable of detecting levels of H₂ down to 200 pM in solution, which approximates the background concentration of H₂ in water exposed to the earth's atmosphere. The response was roughly linear between 0.3 and 300 ppm V of added headspace H ₂ and gave a K_app of 142 nM H_2, when cells were grown anaerobically for 12 h in the presence of H₂. Hydrogen-sensing R. capsulatus cells were grown fermentatively in the dark in co-culture with Chlamydomonas reinhardtii on microtiter plates and the bacteria fluoresced in proportion to H₂ production by the algae. This represents a promising, high-throughput assay for H₂ production in algal libraries, and an enhanced capability for developing H₂ as a clean and renewable fuel.