A conditional upper-bound design map for rhodopsin-augmented electro-microbial CO 2 -to-biomass conversion
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The value of rhodopsin proton pumps as light harvesters in electro-microbial CO 2 -to-biomass conversion depends on molecular photophysics, pathway energetics and reactor light delivery. We couple these scales for Cupriavidus necator , comparing Calvin–Benson–Bassham (CBB) and reductive glycine (rGlyP) assimilation. The model predicts a 17.9% dark rGlyP yield advantage, close to 16.5% measured in chemostats. At 568 nm, 100 PPFD and 45% membrane occupancy, light-derived ATP raises yield by 17% for rGlyP and 14% for CBB. Charging CO 2 capture and formate electrosynthesis, a retinal-only reactor reaches 3.29% efficiency versus 2.56% in the dark. A carotenoid antenna raises this to 3.52% at the model-derived 70% transfer estimate and helps in 93.2% of uncertainty samples, but lowers efficiency at the thermodynamic limit by diverting photons from photovoltaics. Point-source CO 2 cuts the relative light benefit from 38% to 8%. Rhodopsin is therefore most useful when upstream formate is energy-intensive, not as a general efficiency boost.
Highlights
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Predicted 17.9% dark yield gain closely matches chemostat measurements
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Light-derived energy replaces respiratory formate use at similar rates
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A carotenoid antenna helps in 93.2% of matched uncertainty samples
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Point-source carbon dioxide cuts the relative light benefit to 8%
eTOC Blurb
Light-driven proton pumps could reduce the formate that carbon-fixing bacteria consume to make ATP. Saeed et al. link molecular, cellular and reactor constraints, showing how pathway choice, absorption bandwidth and carbon source determine the efficiency of rhodopsin-assisted CO 2 conversion.
