Microalgal triacylglycerols (TAGs) are one of the most promising feedstocks for biofuel production. By systematically analyzing the lipid accumulation and metabolic mechanism of microalgae, the Metabolomics Group in Qingdao Institute of Bioenergy and Bioprocess Technology (QIBEBT) achieved the simultaneous accumulation of neutral lipids and biomass in Nannochloropsis oceanica IMET1, one of the most promising reference photosynthetic microalgae. The results have been published in Algal Research on June 6^th, 2015. 

Microalgal TAG accumulation is commonly triggered in unfavorable environments with stressful conditions, resulting in low biomass production and leading to low TAG yields. Hence, it is an attractive challenge to obtain high production of neutral lipids and biomass simultaneously in the oleaginous microalga. Dr. XIAO Yan and colleagues of the Metabolomics Group in QIBEBT found that the simultaneous accumulation of lipids and biomass can be achieved by enhancing the light intensity to saturation region, when N. oceanica IMET1 is in steady-state continuous cultivation under nitrogen-replete conditions. The lipidomics and metabolomics analyses of the cells in different light intensities indicated that the lipids accumulated under high light (HL) conditions could benefit the biodiesel properties. The authors also found that polar lipids (PLs) could be converted to neutral lipids (NLs), and the contents of osmoprotectants decreased during the lipid accumulation. In addition, the accumulation of carbohydrates was also detected under nitrogen-replete conditions. Among the detected carbohydrates, trehalose was with the highest concentration (~7-11% of total dry biomass), which might play a role of stress protectant or energy source. The element analysis of the biomass indicated that the biomass of N. oceanica IMET1 under HL conditions had the highest C/N ratio and gross calorific value, suggesting that the TAGs obtained under the HL condition was more suitable for biodiesel production. These results indicated that, compared to nutrient-limitation approaches, the employment of high light intensity in light saturation region under nitrogen-replete conditions might be a better strategy for the TAG production in photosynthetic microalgae.  

The research was supervised by Prof. CUI Qiu and Prof. FENG Yingang, and was financially supported by the “One-Three-Five” Projects Fund of the CAS-QIBEBT Director Innovation Foundation, the 863 Program from Ministry of Science and Technology of China, the National Natural Science Foundation of China, and the Shandong Province Scientific Research Foundation for Excellent Young Scientists. 

Figure 1. The cultivation of Nannochloropsis oceanica IMET1 under nitrogen-replete and different light conditions. (A) Schematic view of the continuous culture. (B) Pictures of the final cultivation under different light intensity conditions. (C) The yields of dry cell weight (DCW), lipids, and neutral lipids (NLs) under different light intensity conditions. HL, high light intensity; ML, medium light intensity; LL, low light intensity. (Image by QIBEBT)

Reference:    

Simultaneous accumulation of neutral lipids and biomass in Nannochloropsis oceanica IMET1 under high light intensity and nitrogen replete conditions, Algal Res., 2015, 11, 55-62. 

Contacts:

Prof. CUI Qiu; Prof. FENG Yinggang

Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences

Email: cuiqiu@qibebt.ac.cn; fengyg@qibebt.ac.cn