A hypothesis about the two levels of sec ondary carotenoids synthesis control in algae overproducing carotenoids

Green microalgae Dunaliella salina Te odor. and Haematococcus pluvialis Flotow accumulate large quantities of secondary carotenoids in their cells under certain conditions, induce red “bloom” of certain natural habitats, and are cultured to man ufacture these valuable ingredients for use in food, feed, and cosmetics. Both species have in common that nor l ocalization, neither function of secondary carotenoids relate to photosynthesis. Hyperhalobe D. salina accumulates b-carotene in lipid (triglyceride) gl obules in chloroplast stroma. Freshwater H. pluvial is accumulates astaxanthin in lipid globules outside ch loroplast, in the cytoplasm. Understanding function and synthesis control of secondary carotenoids are ne cessary to optimize industrial culture of these micro algae and complete the knowledge about the role of ca rotenoids in adaptation and biochemical evolution. We propose a hypothesis that secondary carotenoid accumulation in the microalgae is controlled at the two levels: metabolic and signal level. The metabolic level comprises prevailing assimilation of carbon over other limiting nutrients (e.g., nitroge n, phosphorus) that leads to lipid globules accumulation in the algal cells. Environmental stimuli launch signal transduction pathways to induce caroteniod syn thesis and their accumulation in the globules. Our hypothesis is supported by literature data and our findings. In D. salina metabolic con trol level prevails: inhibition of triglyceride synthe sis (Rabbani et al., 1998) or nitrate in the cultur e medium (Coesel et al., 2008) hindered b-carotene accumulation; in multifactor experiment input of ni trogen or phosphorus deficiency into b-carotene accumulation prevailed over the input of high irrad iance and salinity (Komaristaya et al., 2018). In H. pluvialis signal control level prevails: in multifactor e xperiment input of high irradiance into astaxanthin accumulation prevailed over the input of nutrient deficiencies (our data, unpublished). The difference between the two algal species could be due to carbon as similation limitation in D. salina by low carbon dioxide solubility in hyperhaline waters. Research is continued to further develop and check the proposed hypothesis

Green microalgae Dunaliella salina Te odor. and Haematococcus pluvialis Flotow accumulate large quantities of secondary carotenoids in their cells under certain conditions, induce red “bloom” of certain natural habitats, and are cultured to man ufacture these valuable ingredients for use in food, feed, and cosmetics. Both species have in common that nor l ocalization, neither function of secondary carotenoids relate to photosynthesis. Hyperhalobe D. salina accumulates b-carotene in lipid (triglyceride) gl obules in chloroplast stroma. Freshwater H. pluvial is accumulates astaxanthin in lipid globules outside ch loroplast, in the cytoplasm. Understanding function and synthesis control of secondary carotenoids are ne cessary to optimize industrial culture of these micro algae and complete the knowledge about the role of ca rotenoids in adaptation and biochemical evolution. We propose a hypothesis that secondary carotenoid accumulation in the microalgae is controlled at the two levels: metabolic and signal level. The metabolic level comprises prevailing assimilation of carbon over other limiting nutrients (e.g., nitroge n, phosphorus) that leads to lipid globules accumulation in the algal cells. Environmental stimuli launch signal transduction pathways to induce caroteniod syn thesis and their accumulation in the globules. Our hypothesis is supported by literature data and our findings. In D. salina metabolic con trol level prevails: inhibition of triglyceride synthe sis (Rabbani et al., 1998) or nitrate in the cultur e medium (Coesel et al., 2008) hindered b-carotene accumulation; in multifactor experiment input of ni trogen or phosphorus deficiency into b-carotene accumulation prevailed over the input of high irrad iance and salinity (Komaristaya et al., 2018). In H. pluvialis signal control level prevails: in multifactor e xperiment input of high irradiance into astaxanthin accumulation prevailed over the input of nutrient deficiencies (our data, unpublished). The difference between the two algal species could be due to carbon as similation limitation in D. salina by low carbon dioxide solubility in hyperhaline waters. Research is continued to further develop and check the proposed hypothesis