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Biomass and lipid production of a novel freshwater thermo-tolerant mutant strain of Chlorella pyrenoidosa NCIM 2738 in seawater salinity recycled medium

Mehta, Preeti, Rani, Rekha, Gupta, Ravi, Mathur, Anshu Shankar, Puri, Suresh Kumar
Algal research 2018 v.36 pp. 88-95
Chlorella pyrenoidosa, biodiesel, biomass, carbohydrate content, chlorophyll, economic sustainability, freshwater, fuel production, harvesting, heat tolerance, lipids, microalgae, mutants, nutrients, salinity, seawater, temperature
Micro-algae have significant potential for the production of biofuel. It has been previously shown that existing processes of producing micro-algal biofuels are not yet economically viable at commercial scale. Fundamentally, this process will require the implementation of inexpensive harvesting methods and productive algal strains that are tolerant to harsh conditions. The use of freshwater in the large-scale cultivation of microalgae is currently unsustainable; hence, the studies which target the use of seawater medium can reduce the demand of freshwater. Chlorella pyrenoidosa has been extensively studied in freshwater. However, information on the cultivation of C. pyrenoidosa for growth productivity in recycled seawater medium, generated after harvesting through autoflocculation is scarce. In this context, the present study investigates the effect of nutrients sufficient seawater medium following reuse of nutrients exhausted seawater medium on the biochemical composition, biomass and lipid productivities of an in-house developed, thermotolerant strain of C. pyrenoidosa under high temperature (45 °C), outdoor culture conditions. The strain C. pyrenoidosa M18 was found to thrive in seawater medium resulting in increased biomass and lipid productivity. Lipid productivity in seawater medium exceeded 51 mg/Ld−1 which was nearly 2-fold greater than freshwater. Furthermore, the strain was able to grow well and autoflocculate at recycled seawater medium giving biomass and lipid productivities, respectively of 338 mgL−1d−1 and 66 mgL−1d−1. The dry cell weight comprised of 28–32% carbohydrate content when cultivated in recycled seawater medium. Additionally, exposure to high salinity led to an enhanced chlorophyll content as well as increased Fv/Fm ratio. The auto-flocculating property of thermotolerant C. pyrenoidosa M18 strain, in addition to the high biomass and lipid productivities in nutrient exhausted recycled seawater medium, make this microalga an excellent candidate for large-scale outdoor cultivation for biodiesel production.