Abstract
The unicellular marine alga Dunaliella salina is a most interesting green cell factory for the production of carotenes and lipids under extreme environment conditions. However, the culture conditions and their productivity are the major challenges faced by researchers which still need to be addressed. In this study, we investigated the effect of bicarbonate amendment on biomass, photosynthetic activity, biochemical constituents, nutrient uptake and antioxidant response of D. salina during macronutrient deficit conditions (N−, P− and S−). Under nutrient deficit conditions, addition of sodium bicarbonate (100 mM) significantly increased the biomass, carotenoids including β-carotene and lutein, lipid, and fatty acid content with concurrent enhancement of the activities of nutrient assimilatory and carbonic anhydrase enzymes. Maximum accumulation of carotenoid especially β-carotene (192.8 ± 2.11 µg/100 mg) and lipids (53.9%) was observed on addition of bicarbonate during nitrate deficiency compared to phosphate and sulphate deficiency. Supplementation of bicarbonate reduced the oxidative stress caused by ROS, lowered lipid peroxidation damage and improved the activities of antioxidant enzymes (SOD, CAT and APX) in D. salina cultures under nutrient stress.
Highlights
Dunaliella an edible marine microalgae is one of the largest sources of β-carotene (14% of dry weight of cell)
Which has been a major problem since upholding optimum culture condition, escalates the cost of production[21]
Many microalgae have the ability to uptake dissolved inorganic carbon (DIC) from the surrounding for active photosynthesis by CO2 concentrating mechanism[22]
Summary
Dunaliella an edible marine microalgae is one of the largest sources of β-carotene (14% of dry weight of cell). Accumulation of useful molecules in D. salina can be improved by exposing the microalgal cultures to stress by altering several culture conditions including nutrient concentrations (excess or deficit), osmotic pressure fluctuations, temperature fluctuations, light intensity, radiation and pH fluctuations Despite these stress conditions initially improving the amount of desired product, they are detrimental as they limit the overall growth, biomass and the productivity of the algal system due to slowing down the photosynthetic carbon fixation, inhibition of protein synthesis, induction of ROS (reactive oxygen species) in the cell that causes structural defects in chlorophyll, light-harvesting complex and RuBisCO (Ribulose-1,5-bisphosphate carboxylase/oxygenase). Our study focuses on evaluating the combined effect of sodium bicarbonate and macronutrient starvation such as nitrate (N−), phosphate (P−) and sulphate (S−) stress on physiological and biochemical response of D. salina
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