We engineered cyanobacteria to produce a plastic building block at record levels from sunlight and CO₂

How cyanobacteria became efficient chemical factories

My doctoral research focused on turning the cyanobacterium Synechocystis into a better producer of 3-hydroxybutyrate (3HB). 3HB is a simple molecule that can be used to make biodegradable plastics and other chemicals. Unlike traditional industrial processes, these bacteria make it using only sunlight, water and carbon dioxide.

To achieve efficient production levels, the challenge was that the cells need three enzymes working in the right balance. Too much or too little of any one enzyme creates bottlenecks or wastes energy. We therefore built a large library of cyanobacterial strains that carried the same three genes but with randomly different “start signals” (ribosome binding sites) in front of each gene. After screening hundreds of variants, the best strain produced 11.7 grams of 3HB per litre. That is the highest amount ever reported for any organism that grows purely on light and CO₂, and it approaches levels previously achieved only with sugar-fed microbes.

Why this matters beyond the laboratory

Modern industry still relies heavily on fossil resources for plastics and chemicals. Photosynthetic microbes offer a route to the same building blocks while capturing carbon dioxide instead of releasing it. Improving the efficiency of these living factories is one small but concrete step toward more sustainable production of everyday materials.

What the grant year made possible

The final year of the project, supported by the Finnish Foundation for Technology Promotion, was devoted mainly to finishing the written side of the work. Experimental results were already in place, so I concentrated on analysing the data thoroughly, writing the scientific manuscript (of the last required publication) and completing my doctoral thesis. Both the thesis and the manuscript were submitted during the funded period. The funding period made finishing this work possible, and their results and data available to the wider research community.

What I enjoy most about the work

The most rewarding part is seeing how microbial cells can be programmed to perform various tasks, just like a computer. When the right combination of genetic “parts” is put together and the culture starts producing useful chemicals from thin air, the satisfaction is hard to beat. It is a constant reminder that biology still has many innovative solutions waiting to be discovered and applied.

Lauri Kakko received a grant of 26,000 euros from Finnish Foundation for Technology Promotion for his Ph.D. project "Towards competitive photoautotrophic biotechnologies; High-throughput optimization standard for cyanobacterial engineering" in 2025.