The fermentation characteristics of Mortierella alpina were investigated in response to various nitrogen sources. Influences on nitrogen source and glucose uptake rate, mycelial morphology of M. alpina, and pH of medium in relation to different nitrogen sources were discussed. Effects of different nitrogen sources on cell growth, fatty acid composition, arachidonic acid (ARA), and total lipid concentration were also evaluated. It revealed that the maximum nitrogen source uptake ratio was obtained when corn steep liquor was used as nitrogen source. When yeast extract was used as the sole nitrogen source, glucose was completely exhausted at the end of fermentation. The maximum dry cell weight obtained from medium with yeast extract as nitrogen source had the highest total lipid concentration. Sodium nitrate was the favorable nitrogen source for ARA accumulation, and the highest ARA percentage in total fatty acids was obtained, 35.9%. Urea was identified as the favorable nitrogen source for ARA production, the highest ARA concentration obtained from urea was 5.8 g/l. Compared with inorganic nitrogen sources, organic nitrogen compounds are favorable for both cell growth and total lipids accumulation.
Dissolved oxygen (DO) concentration is one of the most important factors affecting microbial cell growth and metabolite formation. In this study, a novel twostage oxygen supply control strategy was applied to enhance oxygen transfer and promote the ability of arachidonic acid production by Mortierella alpina ME-1. Based on process analysis, a two-stage oxygen supply control strategy was proposed in arachidonic acid production in which n-hexadecane was added as an oxygen vector with a final concentration of 4 % at the first of cultivation, the agitation speed was controlled at 180 rpm in the first 96 h, and then switched to 100 rpm. This strategy was experimentally proven to be successful in arachidonic acid fermentation, relatively high arachidonic acid production (15.9 g/L) and dry cell weight (42.5 g/L) was achieved by applying this strategy. The arachidonic acid productivity (2.27 g/L/d) was also successfully improved by 50.3 % and 28.9 %, respectively, compared with fermentations in which agitation speed was kept constant at 180 rpm and under a two-stage agitation speed control strategy.
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