Effects of nitrogen starvation and oxygen limitation on docosahexenoic acid production by Schizochytrium limacinum SR21

Effects of nitrogen and oxygen limitations on docosahexenoic acid(DHA) production by Schizochytrium limacinum SR21 were investigated.Shaking-flask fermentation showed that 0.4 g/L nitrogen concentration was preferred for lipid accumulation and DHA biosynthesis.The optimum ratio of carbon to nitrogen(C/N) was 80:1.Three batches of fermentation were performed in 7 L bioreactor in which Schizochytrium limacinum SR21 was exposed to 1%、5%、10%dissolved oxygen limitation,so as to compare the influence of oxygen limitation on DHA biosynthesis during nitrogen depletion stage.The results indicated that the content of DHA in total fatty acids was 50.95%,44.41%and 38.99%,respectively;and DHA yield was achieved by 7.07,11.5,7.45 g/L,respectively.It showed that lower dissolved oxygen level was favorable for DHA biosynthesis.Combine nitrogen starvation with dissolved oxygen limitation strategy,DHA yield reached 11.5 g/L and was increased by 300%and 50%respectively as compared with those of shaking-flask and sole nitrogen starvation fermentation.As a result,5%dissolved oxygen limitation was most preferred for DHA fermentation during nitrogen depletion stage.