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

Abstract

We isolated and characterized an oleaginous Thraustochytrid microalga. Based on 18s rRNA sequencing, we classified this strain as Schizochytrium sp. SH103. Growth of these cells in a 5L 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 (3L/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. 1.26g/L·h) and total lipid productivity (0.29 vs. 0.61g/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 100.6g/L at 48 h, maximal DCW productivity was 2.1g/L·h, maximal lipid content was 48.6g/L at 48 h, and lipid productivity was 1.0 g/L·h. Additionally, the results of experiments using a 50L MTS fermentor (96.0g/L DCW and 44.3g/L total lipids at 48h) were similar to those using the 5L fermentor. Our results suggest that use of a MTS may help to achieve the efficient fermentation of heterotrophic microalgae for high cell densities.