Accumulation of eicosapentaenoic acid in Nannochloropsis sp. in response to elevated CO sub(2) concentrations

• Published in: Journal of applied phycology Vol. 17; no. 1; pp. 29 - 34
• Main Authors: Hoshida, H, Ohira, T, Minematsu, A, Akada, R, Nishizawa, Y
• Format: Journal Article
• Language: English
• Published: 01.01.2005
• Subjects: Marine; Nannochloropsis
• ISSN: 0921-8971
• DOI: 10.1007/s10811-005-5512-9

To increase eicosapentaenoic acid (EPA, 20:5, n-3) content in the marine alga Nannochloropsis sp., the effect of CO sub(2) concentration during cultivation has been investigated. In a batch culture under normal atmospheric conditions (0.037% CO sub(2)), the EPA content per cell increased during the first 1.5 days and then decreased immediately even though the cells were in an exponential growth phase. Increasing the CO sub(2) concentration to 0.3% and 2% over day 1.5 retained the EPA content at the higher concentration for another 1 and 2 days, respectively, suggesting that the EPA accumulation is enhanced by elevated concentrations of CO sub(2). EPA accumulation in response to elevated CO sub(2) concentrations was also observed during a later growth phase when CO sub(2) was introduced after the decrease of EPA content. The addition of CO sub(2) caused a slight decrease in the pH of the medium though this was not the cause of the observed EPA accumulation as addition of acidic buffer did not affect the EPA content. The maximum EPA production was obtained when 2% CO sub(2) was supplied 12 h prior to the end of the exponential growth. The total EPA production during 4-day cultivation was about twice that obtained with ambient air. These results suggest that the available CO sub(2) concentration affects the EPA content in Nannochloropsis sp.