Effects of shear stress and shear protectants on heterotrophic culture of Haematococcus pluvialis

Abstract

A strategy named “Sequential Heterotrophy-Dilution-Photoinduction” is used for commercial production of astaxanthin in Haematococcus pluvialis. However, shear stress during heterotrophic culture has become the technical bottleneck for the wide application and amplification of this technology in microalgae culture, especially in the heterotrophic culture of H. pluvialis. To clarify the effects of shear stress, the influence of shear stress generated by different aeration rates on the heterotrophic growth of H. pluvialis was first investigated. The results showed that shear stress could cause the transformation of motile cells to non-motile cells, resulting in decrease in growth rate. The critical shear stress was produced by a superficial gas velocity of >3.21 × 10−3 m·s−1. The further analysis based on computational fluid dynamics indicated that shear stress-induced damage to cells was mainly caused by bubble rupture. To reduce the negative effects of shear stress, 0.05 % of Pluronic F-68 was selected for shear protection. Finally, it was successfully applied to the heterotrophic culture of H. pluvialis in a 500 L fermenter, increasing the cell yield by 30.39 %. This study could provide a reference and basis for the control of heterotrophic culture conditions and scale-up of H. pluvialis, and a feasible strategy for reducing the shear stress-induced damage during the heterotrophic process.