Genetic engineering of Haematococcus pluvialis microalgae for the enhancement of astaxanthin production: A review

Haematococcus pluvialis (H. pluvialis) is a significant natural source of astaxanthin, garnering interest in the pharmaceutical and nutraceutical industries. However, astaxanthin production from H. pluvialis is constrained by factors such as a lengthy cultivation period and thick cell walls. Recent research has explored different strategies, such as optimising cultivation conditions, to enhance astaxanthin biosynthesis. This review paper aims to summarise the recent advancement of metabolic and genetic engineering in astaxanthin biosynthesis from H. pluvialis. The review would provide a comprehensive analysis of the molecular components and mechanism involved in the biosynthesis pathway of astaxanthin in H. pluvialis, revealing the specific genes responsible for governing its biosynthesis. Numerous metabolic methodologies are investigated, including manipulating light intensity, salinity, nutrient deficiency, and temperature to enhance microalgae biomass and astaxanthin accumulation. Genetic engineering strategies have recently been studied to manipulate specific genes (e.g. bkt, CrtR-b, pds) to increase astaxanthin production. However, the limitation of genetic engineering is still unclear due to its mechanism of astaxanthin esterification and the transport of secondary β-carotenoids from the chloroplast to the cytosol. This lack of understanding has posed a challenge to maximise astaxanthin production through genetic engineering. This review also provides recent insights and future research directions for genetic engineering by providing a holistic approach to the complex interplay of genetics, metabolism, and biotechnological strategies to maximise astaxanthin production.