Simultaneous accumulation of lipid and carotenoid in freshwater green microalgae Desmodesmus subspicatus LC172266 by nut
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pISSN: 0256-1115 eISSN: 1975-7220
INVITED REVIEW PAPER
INVITED REVIEW PAPER
Simultaneous accumulation of lipid and carotenoid in freshwater green microalgae Desmodesmus subspicatus LC172266 by nutrient replete strategy under mixotrophic condition Chijioke Nwoye Eze*,**,†,‡, Hideki Aoyagi**, and James Chukwuma Ogbonna* *Department of Microbiology, Faculty of Biological Sciences, University of Nigeria, Nsukka, Nigeria **Faculty of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Japan (Received 31 December 2019 • Revised 25 April 2020 • Accepted 30 April 2020) AbstractProduction of biofuel by microalgae can become economically viable if other high-value commercial products such as carotenoid are simultaneously produced. This study aimed at enhancement of lipid and carotenoid productivity by an oleaginous microalga sp. Desmodesmus subspicatus LC172266 by supplementing Nitrogen sources to BG 11 medium under batch or fed batch mixotrophic condition. Optimum urea supplement (0.2 gL 1) to BG 11 medium enhanced carotenoid content of the D. subspicatus by about 3.7 fold (3.02±0.002 mgg1 cell) and 3.0 fold (3.86±0.001 mgg 1 cell) using glucose or glycerol as organic carbon sources, respectively. Also, lipid productivity was enhanced by about 2.0 (0.07817±0.0028 gL1day1) (0.265±0.006 gg 1 cell) and 2.5 (0.08426±0.0008 gL 1day 1) (0.285± 0.02 gg1 cell) fold. Fed-batch cultivation with glucose at a feed rate of 0.5 gL 1 per day enhanced both carotenoid and lipid productivities of D. subspicatus by 34% and 45%, respectively, after eight days of mixotrophic cultivation. Keywords: Lipid Productivity, Desmodesmus subspicatus, Fed-batch Culture, Mixotrophic Culture, Carotenoid
carotenoids in humans and animals [11,25,34] confers higher commercial value on carotenoids than other value-added products by microalgae. Consequently, co-production of bio lipid and carotenoids holds a high prospect for sustainable commercial production of biofuel. However, this prospect has not been actualized, probably because research so far on bio refinery concept by microalgae has focused on the use of cultivation strategies such as stressdependent single phase or biphasic cultivation for accumulation of lipid and/carotenoids [19,24,31]. Unfortunately, the stress factors such as nutrient starvation, high light intensity/temperature/salinity have the disadvantage of low cell growth rate/biomass [31,36], which increases the cost of production by increased cost of downstream processing. Furthermore, the cost of energy for high light intensity or high temperature induction of lipid and/carotenoids [22,24] adds to the cost of production. The biphasic cultivation strategy which involves nutrient-replete and nutrient-limited stages apparently was reported to solve the problem of low biomass associated with stress-dependent single phase strategy [36]. However, the high cost of energy required for the transfer of culture from one phase to another and maintain culture sterility remains the bottle-neck against its cost effectiveness.
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