Researchers in Wuhan Botanical Garden recently established a sequential phototrophic–mixotrophic cultivation (SPMC) strategy to improve the yield of microalgae cultured in open raceway pond. The new culture method has been succeed in its commercial-scale application to lipid-rich microalgae biomass production. This is of great importance to the algal biofuels community. 

By investigating the specific characteristics of Carbon and Nitrogen demand during phototrophic growth of the microalga Graesiella sp. WBG-1, Prof. LI Yeguang and his colleagues identified a window period suitable for culturing the microalga mixotrophically.  

They suggested the SPMC strategy based on this window period to tackle the two fundamental problems of microalgae cultivation: (i) low productivity of photoautotrophic growth, and (ii) bacterial contamination in open outdoor systems. The SPMC regime increased Graesiella biomass and lipid productivity by more than 50% in a 1000 m² raceway pond, compared to phototrophic cultivation, while bacterial reproduction was restrained at a low level.  

The SPMC strategy is well-examined and can be considered a next step towards sustainable and durable algal cultivation, not only for high-efficient large-scale biofuel production, but also for production of high-value chemicals, such as astaxanthin.    

This research was supported by the National High-tech R&D Program of China and the Science and Technology Service Network Initiative of Chinese Academy of Sciences. Results have been published in Biotechnology for Biofuels entitled “Sequential phototrophic–mixotrophic cultivation of oleaginous microalga Graesiella sp. WBG-1 in a 1000 m² open raceway pond”.   

Enhanced growth and lipid accumulation of Graesiella sp. WBG-1 in open raceway pond under SPMC regime(Image by WBG)