In the past decades, the concept of cyanobacterial photosynthetic biomanufacturing has been conceptually demonstrated by the successful synthesis of dozens of natural or non-natural metabolites in cyanobacterial photosynthetic chassis cells. However, the feasibility of cyanobacterial photosynthetic biomanufacturing as economical competitive routes for green production is still questionable.  

To date, cyanobacteria-based photosynthetic production performance remains far less robust than that of conventional biorefinery technologies. Heterologous microbial cell factories are capable of product titers on the order of 100 g/L and productivities surpassing 1000 mg/L/h, while the parameters of cyanobacterial cell factories are generally lower than 10 g/L and 10 mg/L/h.  

Fundamentally, the overall performances of cyanobacterial photosynthetic cell factories are limited by photosynthesis efficiencies of the chassis cells, thus improved photosynthesis capacities is critical to unlock the full potentials of cyanobacterial photosynthetic biomanufacturing. 

In recent years, the rapid accumulation of massive system biology data and development of efficient synthetic biotechnology tools have shed light on deep understanding and comprehensive engineering of the photosynthesis mechanisms in cyanobacteria.  

In addition, the discovery and identification of novel cyanobacteria species with unprecedented growth rates and tolerances to high light and high temperatures also provide more inspirations for modifying and redesigning the cyanobacterial photosynthesis systems.  

Scientists summarized and compared recent progress on the above two aspects. From the levels of light energy utilization and carbon dioxide sequestration, six engineering strategies were summarized, including "spectral expansion for solar energy capture", "antenna reduction for strong illumination tolerance", "electron transport chain optimization", "enhancement of carbon concentration & absorption activity", "enhancement of carbon fixation activity", and "reduction of carbon loss" (Fig. 1).  

Focusing on the industrial application of cyanobacterial photosynthetic biomanufacturing, the development of "smart sensing" and "rapid responsive" system should also be taken into consideration, which would enable the cyanobacteria chassis cells and engineered strains to flexibly adapt to the changing and harsh environmental conditions and to dynamically balance the carbon distribution between cell maintenance and photosynthetic production. 

This work was supported by the National Natural Science Foundation of China, the Shandong Natural Science Foundation, and Strategic Priority Research Program of the CAS. 

Fig. 1. Understanding and engineering strategies for improving cyanobacterial photosynthesis (Image by LUAN Guodong)