Abstract
Microalgae represent a carbon-neutral source of bulk biomass, for extraction of high-value compounds and production of renewable fuels. Due to their high metabolic activity and reproduction rates, species of the genus Chlorella are highly productive when cultivated in photobioreactors. However, wild-type strains show biological limitations making algal bioproducts expensive compared to those extracted from other feedstocks. Such constraints include inhomogeneous light distribution due to high optical density of the culture, and photoinhibition of the surface-exposed cells. Thus, the domestication of algal strains for industry makes it increasingly important to select traits aimed at enhancing light-use efficiency while withstanding excess light stress. Carotenoids have a crucial role in protecting against photooxidative damage and, thus, represent a promising target for algal domestication. We applied chemical mutagenesis to Chlorella vulgaris and selected for enhanced tolerance to the carotenoid biosynthesis inhibitor norflurazon. The NFR (norflurazon-resistant) strains showed an increased carotenoid pool size and enhanced tolerance towards photooxidative stress. Growth under excess light revealed an improved carbon assimilation rate of NFR strains with respect to WT. We conclude that domestication of Chlorella vulgaris, by optimizing both carotenoid/chlorophyll ratio and resistance to photooxidative stress, boosted light-to-biomass conversion efficiency under high light conditions typical of photobioreactors. Comparison with strains previously reported for enhanced tolerance to singlet oxygen, reveals that ROS resistance in Chlorella is promoted by at least two independent mechanisms, only one of which is carotenoid-dependent.
Highlights
Mass culture of microalgae in photobioreactors (PBRs) has gained interest in the past few decades
Car biosynthesis represents an obvious target when aiming to enhance photosynthetic yield of microalgae under photooxidative conditions caused by excess light (EL)
Cells were subjected to two rounds of random chemical mutagenesis with ethyl methanesulfonate (EMS) and mutants were selected for resistance to norflurazon, an inhibitor of carotenogenesis [40]
Summary
Mass culture of microalgae in photobioreactors (PBRs) has gained interest in the past few decades. Beside small-scale traditional cultivations mainly aimed to human or animal feeding, commercial production of algae on a large scale has been identified as a renewable and environmentally sustainable strategy for feedstock production [1]. Both microalgae and land plants catalyze photosynthetic reactions [2], yet the simpler structure of microalgae enhances efficiency in solar energy conversion into biomass respect to plants [3,4,5,6]. Cultivation of microalgae represents a promising source of biomass for many industrial applications, which include production of bioactive compounds, recombinant proteins, livestock feed, biofuels, organic fertilizer and biostimulants [7,8]. The high capacity for nitrogen and phosphorus removal, together with use of flue gas as a source of CO2, makes phycoremediation a valuable circular-economy-based biorefinery [10,11]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
