Functional expression of proton pumps in Rhodobacter sphaeroides enhanced energy supply and photo-fermentative hydrogen production

Photo-fermentative hydrogen production by Rhodobacter sphaeroides (R. sphaeroides) is an energy-consuming process. In this study, a proton-pumping channel (Proteorhodopsin (PR) or Gloeobacter rhodopsin (GR)) was introduced into R. sphaeroides HY01. The results indicated that PR could enhance the biomass of the strain during periods of resource scarcity. The cumulative hydrogen yield of mutant strains (HY01-PR and HY01-GR) increased by 66 % and 75 % compared with HY01 when glucose was fed, respectively. Notably, HY01-GR demonstrated tolerance to high acetate concentrations (93 mM). Moreover, the introduction of proton-pump resulted in a reduction of catabolism carbon flow and the accumulation of various metabolites. This study also confirmed that proton pump overexpression generated more ATP in the late stages of fermentation by coupling ATP synthase. Overall, these findings suggest that proton pumps could potentially be applied to photosynthetic organisms to regulate growth metabolism and enhance the production of valuable compounds.