Potential Use of the Herbicide Quizalofop-p-ethyl for Eicosapentaenoic Acid Overproduction by the Diatom Nitzschia laevis

The diatom Nitzschia laevis is a good alternative source of eicosapentaenoic acid (EPA). Besides strategies for high cell density culture, EPA productivity may be further improved by herbicides. The effect of the herbicide quizalofop-p-ethyl on the growth and EPA production is studied in this article. As the solvent of the herbicide, it was proved that DMSO inhibited the growth and EPA production of N. laevis. The concentration of DMSO in the medium should not exceed 0.2%. Quizalofop-p-ethyl could cause morphology damage to the N. laevis cells. With an increase in concentration of quizalofop-p-ethyl from 0 to 0.4 mmol/L, the dry cell weight production decreased, whereas, at the same time, the lipid content of the dry cell mass increased. When treated with 0.1 mmol/L quizalofop-p-ethyl, the EPA content increased from 3.00% to 3.58% (of dry cell weight, DW), and the proportion of EPA (20:5) in total fatty acids (TFA) increased from 25.15% to 32.88%. These results indicated that the herbicide quizalofop-p-ethyl could stimulate the accumulation of EPA; therefore it might prove useful for selecting algae colonies that overproduce EPA.