From Cyanochemicals to Cyanofactories

As photoautotrophic prokaryotes, cyanobacteria can directly convert CO₂ into organic compounds using solar energy via photosynthesis. Cyanobacteria are important primary producers on the earth and 20-30% organic carbon of the earth come from cyanobacteria photosynthetic carbon fixation. Although cyanobacteria are prokaryotes, cyanobacteria perform oxygenic photosynthesis similar to that of higher plants, with 10 fold higher efficiency. Moreover, the growth cycle of cyanobacteria is much shorter than that of higher plants and recent study show that a cyanobacterial strain can complete one generation in approximately 2 hours. In addition, the gene manipulation of cyanobacteria is much easier than that of higher plants and eukaryotic photosynthetic organism algae. Therefore, engineering cyanobacteria to cyanofactories, in which CO₂ is converted to organic chemicals using solar energy, will be an ideal approach to utilize solar energy and CO₂ to address global energy and environment issues.

In the past 15 years, more than 20 bulk chemicals were synthesized from CO2 in cyanobacteria. This includes C2 chemical, such as ethanol; C3 chemicals, such as acetone and isopropanol; C4 chemical, such as butanol; and C5 chemical, such as isoprene. Theoretically, most of the bulk chemicals that can be produced from sugar by heterotrophic microorganisms, can be produced from CO₂ by engineered cyanobacteria. However, the production efficiency of cyanochemicals is much lower than that produced from sugar by heterotrophic microorganisms. Most cyanochemicals were produced at the level of mg/L and only a few were produced at the level of g/L. Improving cyanochemicals production, with the consideration of CO₂ fixation efficiency, distribution of endogenous carbon flux, conversion efficiency of downstream target chemical synthetic pathway and redox balance, will greatly promote the process from cyanochemicals to cyanofactories. This presentation will cover our recent achievements in this field.