One-step utilization of inulin for docosahexaenoic acid (DHA) production by recombinant Aurantiochytrium sp. carrying Kluyveromyces marxianus inulinase.

This study aimed to express an inulinase gene from the yeast Kluyveromyces marxianus (KmINU) in Aurantiochytrium sp. and realized one-step utilization of inulin resource for DHA production without any chemical pretreatment. An expression cassette with a length of 6052 bp for expressing the inulinase gene was constructed by a fast two-step PCR method and then was transferred into the Aurantiochytrium sp. cells. The Aurantiochytrium sp. recombinant T39 was selected with an inulinase activity up to 50.1 U/mL in 72 h. In a 5-l fed-batch fermentation, as high as 148.9 g/L of inulin was directly used within 120 h, and only 1.2 g/L of total sugar was left in the medium at the end of fermentation. The biomass of 51.4 g/L with a lipid content of 69.2% DCW and a DHA yield of 14.9 g/L was obtained.