Supplementation with rac-GR24 Facilitates the Accumulation of Biomass and Astaxanthin in Two Successive Stages of Haematococcus pluvialis Cultivation

Abstract

The unicellular freshwater green alga Haematococcus pluvialis has attracted much research attention due to its biosynthetic ability for large amounts of astaxanthin, a blood-red ketocarotenoid that is used in cosmetics, nutraceuticals, and pharmaceuticals. Recently, numerous studies have investigated the functions of natural astaxanthin; however, the high cost of the production of astaxanthin from H. pluvialis cultures restricts its commercial viability. There is an urgent need to fulfill commercial demands by increasing astaxanthin accumulation from H. pluvialis cultures. In this study, we discovered that treatment of H. pluvialis cultures at the beginning of the macrozooid stage (day 0) with 1 μM rac-GR24, a synthetic analogue of strigolactones (a class of phytohormones), led to significant increases in biomass [up to a maximum dry cell weight (DCW) of 0.53 g/L] during the macrozooid stage and astaxanthin (from 0.63 to 5.32% of DCW) during the hematocyst stage. We elucidated that this enhancement of biomass accumulation during the macrozooid stage by rac-GR24 is due to its increasing CO 2 utilization efficiency in photosynthesis and carbohydrate biosynthesis. We also found that rac-GR24 stimulated the overproduction of nicotinamide adenine dinucleotide phosphate (NADPH) and antioxidant enzymes in H. pluvialis cultures, which alleviated the oxidative damage caused by reactive oxygen species generated during the hematocyst stage due to the exhaustion of nitrogen supplies. Moreover, rac-GR24 treatment of H. pluvialis synergistically altered the activity of the pathways of fatty acid biosynthesis and astaxanthin esterification, which resulted in larger amounts of astaxanthin being generated by rac-GR24-treated cultures than by controls. In summary, we have developed a feasible and economic rac-GR24-assisted strategy that increases the amounts of biomass and astaxanthin generated by H. pluvialis cultures, and have provided novel insights into the mechanistic roles of rac-GR24 to achieve these effects.

Purple acid phosphatase promoted hydrolysis of organophosphate pesticides in microalgae

“…The CO 2 utilization efficiency of P. tricornutum cultures was assessed using 500 mL Duran laboratory bottles with stainless steel two-port connector gaps and calculated based on the input and output quantities of CO 2 using gas chromatography (Shimadzu, Japan). Furthermore, for enzyme extraction, the centrifuged P. tricornutum pellets were ground in liquid nitrogen with the pre-mixed solutions and the activities of two representative enzymes involved in photosynthesis, namely ribulose-1,5-bisphosphate carboxylase-oxygenase (RuBisCO) and carbonic anhydrase, were measured following previously reported protocols [ 27 ].…”

Cytochrome P450-mediated co-metabolism of fluoroquinolones by Haematococcus lacustris for simultaneously promoting astaxanthin and lipid accumulation

“…3D). Apart from the alleviation function of NADPH to oxidative stress, NADPH also exhibited a major reducing equivalent for the biosynthesis of microalgae-based metabolites [19]. Based on these data, thus, it is assumed that the increase of ATP and NADPH stimulated by glycerol may provide enough reducing equivalents for concurrently alleviating oxidative damage and improving microalgae-based products.…”

“…Previous studies have demonstrated that molecular analyses of microalgae could reveal the potential mechanism of responses by numerous treatments [19,31]. As shown in Fig.…”

“…It is worthwhile noting that the removal efficiency of antibiotics is highly based on the species of microalgae [18]. Haematococcus lacustris (previously named Haematococcus pluvialis), as a unicellular green alga, is capable of assimilation nutrients for valuable astaxanthin production with a concentration ranging from 2 to 4% of dry cell weight (DCW) [19]. Relevant studies demonstrated the relatively high removal efficiency of different antibiotics by H. lacustris and thus, it is theoretically feasible to regard H. lacustris as a promising microalgal strain of fluoroquinolone antibiotics removal [20,21].…”

Polyphenol regulates metabolic and physiological properties of microalgae to accumulate biocompounds

“…Cellular biomass was determined following the protocol reported by Li et al (2019) [24]. Growth curve was generated by the direct count method and photosynthetic e ciency including maximal photochemical e ciency (Fv/Fm), relative electron transport rate (rETR), and non-photochemical quenching (NPQ) were measured by a pulse amplitude-modulated (PAM) uorometer (Water-PAM uorometer, Germany) described previously [25].…”