Effect of consumed carbon to nitrogen ratio on mycelial morphology and arachidonic acid production in cultures of Mortierella alpina

The influence of the consumed carbon to nitrogen.(C/N) ratio on arachidonic acid (AA) production and mycelial morphology was investigated in cultures of Mortierella alpina using shake flasks and a fermenter. The consumed C/N ratio was varied from 5 to 32 under the condition that the total initial am ount of carbon and nitrogen sources was 50 g/l. Cellular yield increased ma rkedly at C/N ratios below 7; carbon utilization was switched from cellular growth to lipid biosynthesis in the C/N ratio range of 7-15; lipid biosynt hesis was most active when the C/N ratio was in the range of 15-32. However , for C/N ratios higher than 15, the mycelial concentration decreased due t o nitrogen limitation but the lipid yield still increased. In the presence of excess nitrogen, the biomass concentration depended on the amount of the nitrogen source, but the AA yield was inversely related to this. On the ot her hand, in the presence of excess carbon, the fatty acid concentration in creased with carbon source concentration but the AA concentration remained constant. From the viewpoint of AA production, the optimum C/N ratio was in the range of 15 to 20 with a balance between the amounts of carbon and nit rogen sources. When an enriched medium was used at a fixed C/N ratio of 20, the cellular and AA concentrations were shown to be proportional to the to tal concentrations of carbon and nitrogen sources in both flasks and the fe rmenter. The whole pellet size and width of pellet annular regions did not change with increasing C/N ratio for C/N ratios below 20 in the bask cultur es. However, when the C/N ratio was higher than 20, these sizes increased i n proportion to the C/N ratio.