Effects of mineral addition on the growth morphology of and arachidonic acid production by Mortierella alpina 1S-4

The culture conditions for arachidonic acid (AA) production by Mortierella alpina 1S-4 were investigated by means of a morphological study with the aims of obtaining a high AA yield and scale-up. In a 50-L jar fermentor study, a medium containing 3.1% soy flour and 1.8% glucose with 0.3% KH₂PO₄, 0.1% Na₂SO₄, 0.05% CaCl₂·2H₂O and 0.05% MgCl₂·6H₂O was found to be optimum. The AA yield reached 9.8 g/L/7 d, and the major morphology was small pellets (1–2 mm). However, in the case of the only addition of KH₂PO₄, the major morphology was filaments. The apparent viscosity increased to 2240 cp, thereby requiring a high agitation speed to maintain adequate oxygen tension, which caused mycelial damage due to shear stress and therefore a decrease in the AA yield. When a medium with Na₂SO₄, CaCl₂, and MgCl₂ was used, the major morphology was large pellets (2–3 mm), and mass transfer limitation through the pellet wall caused a decrease in the AA yield. Based on these results, a scale-up study was carried out under the optimal conditions described above. An AA yield of 10.9 g/L/8 d was obtained in a 10-kL industrial fermentor, and the major morphology was small pellets.