Over 4 months of ethylene production using solid-state photosynthetic cell factories

This study demonstrates the feasibility of solid-state photosynthetic cell factories for long-term ethylene production. Engineered Synechocystis sp. PCC 6803 expressing the ethylene-forming enzyme was immobilized in 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO)-oxidized cellulose nanofiber (TCNF) matrices, using 200-μm Ca²⁺–polyvinyl alcohol–TCNF hydrogel films or a 2-mm all-polysaccharide Ca²⁺–mixed-linkage glucan–TCNF film. The solid-state thin-layer architecture supported long-term ethylene production by limiting biomass accumulation, improving light utilization, and enabling more stable biocatalytic performance. Operated in a custom photobiofilm reactor under continuous-flow semi-wet cultivation, these biocatalysts sustained ethylene production for over 4 months, achieving up to twofold higher yields compared with continuous-flow suspension cultures. The suspension system itself demonstrated 4-month ethylene production in cyanobacteria. Biodegradation assays confirmed the environmental compatibility of TCNF matrices, with the all-polysaccharide formulation offering additional sustainability advantages. Overall, these results demonstrate the potential of solid-state photosynthetic cell factories as a sustainable platform for the photosynthetic production of solar chemicals and fuels.