Engineered Bacterial Teams Turn Sunlight and CO2 Into 1-Butanol

Scientists at Uppsala University have taken a significant step toward a long-sought goal in industrial biotechnology: using sunlight and carbon dioxide to feed engineered microbes that churn out valuable chemicals. In a study published in Applied Microbiology and Biotechnology, Stamatina Roussou and Peter Lindblad describe synthetic two-member microbial consortia in which a photosynthetic cyanobacterium converts CO2 into acetate, which then serves as the sole carbon source for engineered heterotrophic bacteria producing 1-butanol, an industrially relevant bulk chemical and potential biofuel.

Synthetic consortia represent an emerging frontier in biotechnology, and their appeal lies in the principle of division of labor. Rather than cramming every metabolic function into a single organism, researchers can distribute tasks across specialized members, each optimized for its role. This approach reduces the metabolic burden on any one cell, improves robustness, and, according to the authors, offers a reduced risk of contamination because the engineered partners occupy the ecological niche that invaders would otherwise exploit. Consortia that combine phototrophic and heterotrophic bacteria are especially attractive because the phototrophic partner can harvest light energy and fix atmospheric CO2, effectively converting an abundant greenhouse gas into organic carbon that sustains the rest of the community.

Most previous explorations of such phototrophic–heterotrophic partnerships have relied on sucrose as the transferred carbon source. Sucrose, however, is a relatively large molecule, and its export and import require dedicated transport machinery. Acetate offers a simpler alternative. It is a small two-carbon compound produced naturally as a by-product by many microorganisms, including the model cyanobacterium Synechocystis PCC 6803, the workhorse of cyanobacterial synthetic biology. The catch is that wild-type cyanobacteria secrete only trace amounts of acetate during phototrophic growth—far too little to support a productive industrial partnership.

The Uppsala team solved this problem in earlier work through targeted metabolic engineering. By introducing a phosphoketolase, or PK, an enzyme that reroutes carbon flux through the central carbon metabolism of the cyanobacterium, and by overexpressing phosphotransacetylase, or Pta, the enzyme that channels acetyl-phosphate toward acetate, they created a high-producing strain designated WT_PKPa_RBS_BsPta_Δacs. The acs deletion prevents re-assimilation of secreted acetate, locking the cell into an export phenotype. The resulting organism secretes significant levels of acetate into its growth medium, turning it into a living, sunlight-powered carbon factory.

With the acetate donor in hand, the next challenge was to build reliable consumers. Roussou and Lindblad engineered two different heterotrophs for 1-butanol production: Escherichia coli, the standard bacterium of metabolic engineering, and Pseudomonas taiwanensis, a robust soil-dwelling species increasingly favored for its tolerance of harsh conditions. Both strains were first cultivated on acetate as their sole carbon source, demonstrating that they could grow on the very molecule the engineered cyanobacterium produces. Only after this critical validation were the partners combined.

The researchers then established two distinct synthetic consortia, pairing the acetate-secreting Synechocystis strain individually with each of the butanol-producing heterotrophs. Remarkably, the co-cultures were maintained for 42 days, an extended duration that speaks to the stability of the engineered partnerships. Throughout the experiment, the team successfully monitored growth dynamics, tracking how each member of the community fared over more than a month of continuous co-existence under phototrophic conditions.

The measurements told a coherent story. Acetate concentrations in the consortia were lower than in a corresponding axenic Synechocystis culture, a difference that indicates the heterotrophic partners were actively consuming the carbon being secreted by the cyanobacteria. In other words, the engineered phototroph was not merely dumping acetate into the medium; it was feeding its partners. Crucially, 1-butanol was detected in both co-cultures, confirming that the transferred photosynthetic carbon was being converted into the desired end product by the engineered E. coli and P. taiwanensis strains.

This demonstration is conceptually important because it closes a loop that many in the field have tried to close. Photosynthetic microbes can fix CO2 with sunlight, but they are often inefficient producers of complex chemicals. Heterotrophic microbes are superb synthetic chemists but need organic feedstocks, which typically come from plant biomass or sugar in conventional biorefineries. By coupling the two through acetate, the study shows that a renewable, food-independent supply chain is technically feasible: sunlight and CO2 in, acetate out of one organism, and 1-butanol out of another, all within a single co-culture vessel.

1-Butanol itself is a compelling target. It is a four-carbon alcohol with fuel properties closer to gasoline than ethanol, making it attractive as a drop-in biofuel or blending component, and it also serves as a precursor for paints, coatings, polymers, and solvents. Industrial production currently relies on petrochemical routes or on traditional Clostridium fermentations that require sugar feedstocks and suffer from solvent toxicity to the producing organism. Outsourcing butanol synthesis to heterotrophs fed by a photosynthetic partner could, in principle, decouple production from agricultural inputs while the cyanobacterium simultaneously captures CO2.

The work, funded by the European Union’s Horizon 2020 research and innovation program under the PROMICON project, also carries practical lessons for the broader synthetic ecology community. Maintaining a stable consortium for six weeks shows that carefully matched production and consumption rates can keep the partnership in balance, and the detectable butanol titers in both pairings suggest the acetate channel is robust across different heterotrophic chassis. Challenges remain before such systems approach industrial relevance, including raising acetate secretion rates, improving butanol titers and tolerance, and scaling photobioreactor conditions. Yet the study establishes a clear proof of principle: photosynthetically derived acetate can sustain heterotrophic production of a value-added bulk chemical in a designed microbial community, charting a path toward sunlight-driven biomanufacturing built on cooperation rather than a single overloaded cell.

Subject of Research: Synthetic phototrophic-heterotrophic bacterial consortia engineered to convert photosynthetically derived acetate into 1-butanol

Article Title: Synthetic consortia towards photosynthetically derived acetate for heterotrophic production of 1-butanol

Article References: Roussou, S., & Lindblad, P. (2026). Synthetic consortia towards photosynthetically derived acetate for heterotrophic production of 1-butanol. Applied Microbiology and Biotechnology, 110(1), Article 268. https://doi.org/10.1007/s00253-026-14029-z

Image Credits: AI Generated

DOI: 10.1007/s00253-026-14029-z

Keywords: synthetic consortia, Synechocystis PCC 6803, Escherichia coli, Pseudomonas taiwanensis, acetate, 1-butanol, cyanobacteria, metabolic engineering, synthetic biology, CO2 fixation, biofuels, phototrophic-heterotrophic co-culture