Effects of Salinity on the Growth Performance and Docosahexaenoic Acid Positional Distribution in Triacylglycerols of the Newly Isolated <i>Schizochytrium</i> sp. FJ-1

<i>Schizochytrium</i>-derived omega-3 polyunsaturated fatty acids (e.g., docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA)) are proven to be health-beneficial bioactive substances that have been widely applied in the pharmaceutical, nutraceutical, and food industries. In this work, the newly isolated <i>Schizochytrium</i> sp. FJ-1 strain was selected to investigate the effects of salinity on the growth performance, lipid production, DHA yield, and positional distribution of triacylglycerols (TAGs). In addition, <i>Schizochytrium</i> sp. 20888 was used as a control strain. The obtained results showed that <i>Schizochytrium</i> sp. FJ-1 could grow with a low biomass in the absence of sea salt; however, <i>Schizochytrium</i> sp. 20888 did not grow in the medium without sea salt. Moreover, <i>Schizochytrium</i> sp. FJ-1 achieved the highest biomass in 10‰ salinity, whilst <i>Schizochytrium</i> sp. 20888 attained the greatest biomass in 40‰ salinity. In terms of the total lipid content and TAG fraction percentage, <i>Schizochytrium</i> sp. FJ-1 grown in 5–20‰ salinity had high total lipid contents (57.04–60.02%), with TAGs accounting for over 90% of the lipid fraction. The highest DHA contents for total lipids (41.38%) and TAGs (40.18%) were obtained when <i>Schizochytrium</i> sp. FJ-1 was grown under 10‰ salinity conditions. Additionally, under the same culture condition, EPA contents of lipids and TAGs were significantly higher for <i>Schizochytrium</i> sp. FJ-1 compared with <i>Schizochytrium</i> sp. 20888. Furthermore, nuclear magnetic resonance analysis found that the salinity level had a distinct impact on the positional distribution of DHA in TAGs in these two <i>Schizochytrium</i> strains. <i>Schizochytrium</i> sp. FJ-1 grown under 40‰ salinity conditions produced TAGs with the greatest percentage of <i>sn</i>-2 DHA (81.24%). The percentages were higher than those found for the other groups of this microalga and <i>Schizochytrium</i> sp. 20888. Taken together, <i>Schizochytrium</i> sp. FJ-1 could be a potential candidate to produce highly valued DHA lipids or TAG bioproducts by regulating salinity.