Improving astaxanthin production of Haematococcus pluvialis by an efficient fed-batch strategy in a photobioreactor

Abstract

Astaxanthin has attracted extensive attention due to its multiple physiological functions, but its production from Haematococcus pluvialis remains challenging due to low biomass concentration. In this study, an efficient fed-batch strategy was designed to improve the astaxanthin productivity at a stable pH level during mixotrophic growth of H. pluvialis. The acid feeding position was equipped with feeding medium to provide sufficient nutrients based on pH changes. Results suggested that pH level was increasing during acetate cultivation, and was a limiting factor for H. pluvialis growth. The biomass concentration was enhanced by 25.7% through stabilizing pH levels in batch culture. Based on linear relationship between nutrient consumption and pH change, a fed-batch strategy was designed and tested, increasing the biomass concentration by 90.6% to 1.62 g L−1 in the photobioreactor. At the molecular level, the photosynthetic efficiency was limited by reducing Rubisco activity and increasing NADPH oxidase activity, while carbon metabolism was enhanced by elevating pyruvate and ace-CoA contents. Furthermore, astaxanthin productivity was increased to 4.5 mg L−1 d−1 within pH range from 5 to 6, which was accompanied by the elevated pyruvate, ace-CoA, and lipid contents. The fed-batch strategy was promising for microalgal production due to its easy operation and high astaxanthin productivity.