Synthetic consortia towards photosynthetically derived acetate for heterotrophic production of 1-butanol.

Synthetic consortia is an emerging field in biotechnology, offering advantages such as division of labor between the individual members and reduced risk of contamination. Consortia combining phototrophic and heterotrophic bacteria are attractive, as phototrophs can utilize CO₂ and light energy to sustain growth. Several studies have explored such systems where sucrose is most commonly used as the provided carbon source. An alternative is acetate, a smaller two-carbon molecule produced as a by-product by many microorganisms, including the model cyanobacterium Synechocystis PCC 6803 (thereafter Synechocystis). Although acetate production during phototrophic growth is typically low, previous studies have demonstrated that metabolic engineering-specifically the introduction of phosphoketolase (PK) and overexpression of phosphotransacetylase (Pta)-enabled the development of a high-producing strain (WT_PKPa_RBS_BsPta_Δacs) capable of secreting significant levels of acetate into the medium (Roussou and Lindblad 2026). In this study, Escherichia coli and Pseudomonas taiwanensis were engineered to produce 1-butanol, an industrially relevant bulk chemical, and cultivated using acetate as the sole carbon source. These strains were then individually co-cultivated with the previously engineered Synechocystis strain, WT_PKPa_RBS_BsPta_Δacs, forming two distinct consortia that were maintained for 42 days. Growth dynamics were successfully monitored, and acetate concentrations in the consortia were lower than in a corresponding axenic Synechocystis culture. At the same time, 1-butanol production was detected in the two co-cultures, demonstrating the feasibility of coupling photosynthetically derived acetate to heterotrophic production of a value-added bulk chemical. KEY POINTS: • Photosynthetic/heterotrophic synthetic consortia for 1-butanol production. • Engineered Synechocystis PCC 6803 cells produce acetate from CO