Background: Whole-cell biotransformation is a promising emerging technology for the production of chemicals. When using heterotrophic organisms such as E. coli and yeast as biocatalysts, the dependence on organic carbon source impairs the sustainability and economic viability of the process. As a promising alternative, photosynthetic cyanobacteria with low nutrient requirements and versatile metabolism, could ofer a sustainable platform for the heterologous production of organic compounds directly from sunlight and CO2. This strategy has been applied for the photoautotrophic production of sucrose by a genetically engineered cyanobacterium, Synechocystis sp. PCC 6803 strain S02. As the key concept in the current work, this can be further used to generate organic carbon compounds for diferent heterotrophic applications, including for the whole-cell biotransformation by yeast and bacteria.

Results: Entrapment of Synechocystis S02 cells in Ca2+-cross-linked alginate hydrogel beads improves the specifc sucrose productivity by 86% compared to suspension cultures during 7 days of cultivation under salt stress. The process was further prolonged by periodically changing the medium in the vials for up to 17 days of efcient production, giving the fnal sucrose yield slightly above 3000 mg l −1 . We successfully demonstrated that the medium enriched with photosynthetically produced sucrose by immobilized Synechocystis S02 cells supports the biotransformation of cyclohexanone to ε-caprolactone by the E. coli WΔcscR Inv:Parvi strain engineered to (i) utilize low concentrations of sucrose and (ii) perform biotransformation of cyclohexanone to ε-caprolactone.

Conclusion: We conclude that cell entrapment in Ca2+-alginate beads is an efective method to prolong sucrose production by the engineered cyanobacteria, while allowing efcient separation of the cells from the medium. This advantage opens up novel possibilities to create advanced autotroph–heterotroph coupled cultivation systems for solar-driven production of chemicals via biotransformation, as demonstrated in this work by utilizing the photosynthetically produced sucrose to drive the conversion of cyclohexanone to ε-caprolactone by engineered E. coli.