Improving carbohydrate and starch accumulation inChlorellasp. AE10 by a novel two-stage process with cell dilution.
BACKGROUND
Microalgae are highly efficient cellular factories that capture CO2and are also alternative feedstock for biofuel production. Carbohydrates, proteins, and lipids are major biochemical components in microalgae. Carbohydrates or starch in microalgae are possible substrates in yeast fermentation for biofuel production. The carbon partitioning in microalgae could be regulated through environmental stresses, such as high concentration of CO2, high light intensity, and nitrogen starvation conditions. It is essential to obtain carbohydrate-rich microalgae via an optimal bioprocess strategy.


RESULTS
The carbohydrate accumulation in a CO2tolerance strain,Chlorellasp. AE10, was investigated with a two-stage process. The CO2concentration, light intensity, and initial nitrogen concentration were changed drastically in both stages. During the first stage, it was cultivated over 3 days under 1% CO2, a photon flux of 100 μmol m-2s-1, and 1.5 g L-1NaNO3. It was cultivated under 10% CO2, 1000 μmol m-2s-1, and 0.375 g L-1NaNO3during the second stage. In addition, two operation modes were compared. At the beginning of the second stage of mode 2, cells were diluted to 0.1 g L-1and there was no cell dilution in mode 1. The total carbohydrate productivity of mode 2 was increased about 42% compared with that of mode 1. The highest total carbohydrate content and the highest starch content of mode 2 were 77.6% (DW) and 60.3% (DW) at day 5, respectively. The starch productivity was 0.311 g L-1day-1and the total carbohydrate productivity was 0.421 g L-1day-1in 6 days.


CONCLUSIONS
In this study, a novel two-stage process was proposed for improving carbohydrate and starch accumulation inChlorellasp. AE10. Despite cell dilution at the beginning of the second stage, environmental stress conditions of high concentration of CO2, high light intensity, and limited nitrogen concentration at the second stage were critical for carbohydrate and starch accumulation. Although the cells were diluted, the growths were not inhibited and the carbohydrate productivity was improved. These results were helpful to establish an integrated approach from CO2capture to biofuel production by microalgae.
Shanghai Advanced Research Institute, Chinese Academy of Sciences, 99 Haike Road, Shanghai, 201210 China.|University of Chinese Academy of Sciences, 19 Yuquan Road, Beijing, 100049 China.|ShanghaiTech University, 100 Haike Road, Shanghai, 201210 China.
Dujia
D
Cheng
Shanghai Advanced Research Institute, Chinese Academy of Sciences, 99 Haike Road, Shanghai, 201210 China.
Dengjin
D
Li
Shanghai Advanced Research Institute, Chinese Academy of Sciences, 99 Haike Road, Shanghai, 201210 China.|University of Chinese Academy of Sciences, 19 Yuquan Road, Beijing, 100049 China.|ShanghaiTech University, 100 Haike Road, Shanghai, 201210 China.
Yizhong
Y
Yuan
Shanghai Advanced Research Institute, Chinese Academy of Sciences, 99 Haike Road, Shanghai, 201210 China.
Lin
L
Zhou
Shanghai Advanced Research Institute, Chinese Academy of Sciences, 99 Haike Road, Shanghai, 201210 China.
Xuyang
X
Li
Shanghai Advanced Research Institute, Chinese Academy of Sciences, 99 Haike Road, Shanghai, 201210 China.
Tong
T
Wu
Shanghai Advanced Research Institute, Chinese Academy of Sciences, 99 Haike Road, Shanghai, 201210 China.
Liang
L
Wang
Shanghai Advanced Research Institute, Chinese Academy of Sciences, 99 Haike Road, Shanghai, 201210 China.|ShanghaiTech University, 100 Haike Road, Shanghai, 201210 China.
Quanyu
Q
Zhao
Shanghai Advanced Research Institute, Chinese Academy of Sciences, 99 Haike Road, Shanghai, 201210 China.|ShanghaiTech University, 100 Haike Road, Shanghai, 201210 China.
Wei
W
Wei
Shanghai Advanced Research Institute, Chinese Academy of Sciences, 99 Haike Road, Shanghai, 201210 China.|ShanghaiTech University, 100 Haike Road, Shanghai, 201210 China.
Yuhan
Y
Sun
Carbohydrate; Chlorella; Light intensity; Nitrogen starvation; Starch