Photohydrogenotrophic Cultivation of Purple Non-Sulfur Bacteria in an Open Bioreactor: Enhanced Selectivity Through...

This work pioneers in photohydrogenotrophic cultivation of Rhodobacter capsulatus in an open, non-axenic bubble column reactor to maximize biomass productivity and selectivity for purple non-sulphur bacteria. Using full-spectrum light and non-limiting ammonium levels, biomass productivity reached up to 0.98 gTSS L^-1 d^-1. To enhance microbial selectivity, two operational strategies were tested: (i) alternating of full light spectrum exposure and infrared light which increased pigment production (15 ± 1 mg bacteriochlorophyll gVSS^-1 and 4.7 ± 0.5 mg carotenoids gVSS^-1) and protein content (0.78 ± 0.22 g protein gVSS^-1) while minimizing microalgae content and (ii) ammonium limitation that stimulated the biological nitrogen fixation capability of purple non-sulphur bacteria, resulting in the highest purple non-sulfur bacteria abundance, representing up to 96% of the prokaryotic community, without compromising on productivity. These results demonstrate the feasibility of open culture photohydrogenotrophic cultivation, offering a stepstone to scalable and ecologically aligned alternative for microbial protein production for food and biobased applications.