Effects of dissolved oxygen on the morphology of an arachidonic acid production by Mortierella alpina 1S-4

Arachidonic acid (AA) production by Mortierella alpina 1S-4 was investigate d using a 50-L fermenter. In order to optimize the dissolved oxygen (DO) co ncentration and to investigate the effect of DO on morphology, cultivation was carried out under constant DO at various levels in the range of 3-50 pp m. To maintain a DO concentration above 7 ppm, two methods, i.e., the oxyge n-enrichment (OE) method (experimental range, 25-90% oxygen gas supplied) a nd the pressurization (PR) method (experimental range, 180-380 kPa headspac e pressure), were used. As a result, the optimum DO concentration range was found to be 10-15 ppm. In this optimum DO concentration range, the AA yiel d was enhanced about 1.6-fold compared to that obtained at 7 ppm DO, and th ere was no difference in the AA productivity between the OE and PR methods. When the DO concentration was maintained at 20-50 ppm using the OE method, the morphology changed from filaments to pellets, and the AA yield decreas ed drastically because of stress due to the limited mass transfer through t he pellet wall. When the DO concentration was maintained at 15-20 ppm using the PR method, the morphology did not change, and the AA yield decreased g radually. (C) 1999 John Wiley & Sons, Inc.