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Boosting productivity of heterotrophic microalgae by efficient control of the oxygen transfer coefficient using a microbubble sparger

Ju, Jung-Hyun, Oh, Beak-Rock, Ko, Dong-Jin, Heo, Sun-Yeon, Lee, Jong-Jea, Kim, Young-Min, Yang, KwonSeok, Seo, Jeong-Woo, Hong, Won-Kyung, Kim, Chul-Ho
Algal research 2019 v.41 pp. 101474
Schizochytrium, aeration, agitation, batch fermentation, fermenters, lipid content, lipids, microalgae, microbubbles, oxygen, ribosomal RNA, sequence analysis
We isolated and characterized an oleaginous Thraustochytrid microalga. Based on 18 s rRNA sequencing, we classified this strain as Schizochytrium sp. SH103. Growth of these cells in a 5 L fermentor with a microbubble-type sparger (MTS) efficiently increased the oxygen transfer coefficient (OTC), while inducing only low external stress. For fermentation under conditions of low agitation (100 rpm) and aeration (3 L/min), the OTC was 8.6-fold higher using a MTS than a general type sparger (GTS). Under these same conditions, dry cell weight (DCW) productivity (0.54 vs. 1.26 g/L·h) and total lipid productivity (0.29 vs. 0.61 g/L·h) were each about 2.2-fold higher using a MTS than a GTS. Under conditions that optimized the OTC in a MTS fermentor (876 h−1), DCW productivity, total lipid productivity and DHA productivity were each 1.3-fold greater than non-optimized condition. Fed-batch fermentation experiments indicated the maximal DCW was 100.6 g/L at 48 h, maximal DCW productivity was 2.1 g/L·h, maximal lipid content was 48.6 g/L at 48 h, and lipid productivity was 1.0 g/L·h. Additionally, the results of experiments using a 50 L MTS fermentor (96.0 g/L DCW and 44.3 g/L total lipids at 48 h) were similar to those using the 5 L fermentor. Our results suggest that use of a MTS may help to achieve the efficient fermentation of heterotrophic microalgae for high cell densities.