Chemicals to enhance microalgal growth and accumulation of high-value bioproducts

Abstract

Photosynthetic microalgae have attracted significant attention as they can serve as important sources for cosmetic, food and pharmaceutical products, industrial materials and even biofuel biodiesels. However, current productivity of microalga-based processes is still very low, which has restricted their scale-up application. In addition to various efforts in strain improvement and cultivation optimization, it was proposed that the productivity of microalga-based processes can also be increased using various chemicals to trigger or enhance cell growth and accumulation of bioproducts. Herein, we summarized recent progresses in applying chemical triggers or enhancers to improve cell growth and accumulation of bioproducts in algal cultures. Based on their enhancing mechanisms, these chemicals can be classified into four categories:chemicals regulating biosynthetic pathways, chemicals inducing oxidative stress responses, phytohormones and analogs regulating multiple aspects of microalgal metabolism, and chemicals directly as metabolic precursors. Taken together, the early researches demonstrated that the use of chemical stimulants could be a very effective and economical way to improve cell growth and accumulation of high-value bioproducts in large-scale cultivation of microalgae.

Comparative assessment of Ni and As(III) mediated alterations in diazotrophic cyanobacteria, Anabaena doliolum and Anabaena sp. PCC7120

“…Carotenoids are known to be major players of antioxidant response against ROS and found to be increased under metal stress (Yu et al, 2015). Significant decrement in phycocyanin content was noticed at all days of treatment under both Ni and As(III) stress in both species.…”

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“…Therefore, significant pH changes were also detected (Figure 1b). Observed results clearly show diauxic growth of E. gracilis [7]. Aeration rate and stirrer speed was also changed to promote optimal condition for microalgae cultivation and lipid production (Figure 2a & 2b).…”

Identification and mechanism analysis of chemical modulators enhancing astaxanthin accumulation in Haematococcus pluvialis

“…In addition to various efforts to improve growth and astaxanthin accumulation [5,6,13], as an alternative approach, chemicals, which served as metabolic triggers or enhancers that are able to directly adjust cellular metabolism, could be applied in H. pluvialis to improve production or accumulation of astaxanthin [14,15]. For example, reactive oxygen species (ROS), such as H 2 O 2 , 2,2′-azo-bis(2-amidinopropane)-dihydrochloride (AAPH) for peroxy radical (AO 2 •), methylene blue (MB) for singlet oxygen ( 1 O 2 ), and methyl viologen (MV) for superoxide anion radical (O 2 − ), were demonstrated to induce astaxanthin accumulation to about 50 pg/cell in H. pluvialis [16]; more recent studies showed that astaxanthin accumulation could be enhanced by jasmonic acid (JA), salicylic acid (SA), gibberellic acid (GA 3 ), abscisic acid (ABA) and 2,4-epibrassinolide (EBR); and the enhancing effects of the chemicals were concentration-dependent [17][18][19][20].…”