Improvement of docosahexaenoic acid fermentation from sp. AB-610 by staged pH control based on cell morphological changes.

sp. AB-610 accumulates relatively higher amount of DHA-rich lipid in the cells, and it was found that DHA yield was closely related to the cell morphology and pH value during fermentation period. DHA production from sp. AB-610 in fed-batch fermentation was investigated and four growth stages were clarified as lag stage, balanced growth stage, lipid accumulation stage, and lipid turnover stage, based on the morphologic observation and key parameters changes. Then a simple strategy of two-stage pH control was developed, in which pH 7.0 was kept until 12 h after the end of balanced growth stage, and then shifted to 5.0 for the rest period in fermentation. A maximal DHA production of 11.44g/L was achieved. This approach has advantage of easy scaling up for industrial DHA fermentation from sp. cells.