Tailoring Microalgae for Efficient Biofuel Production

Abstract

Depleting fossil fuel, soaring prices, growing demand, and global climate change concerns have driven the research for finding an alternative source of sustainable fuel. Microalgae have emerged as a potential feedstock for biofuel production as many strains accumulate higher amounts of lipid, with faster biomass growth and higher photosynthetic yield than their land plant counterparts. In addition to this, microalgae can be cultured without needing agricultural land or ecological landscapes and offer opportunities for mitigating global climate change, allowing waste water treatment and carbon dioxide sequestration. Despite these benefits, microalgae pose many challenges, including low lipid yield under limiting growth conditions and slow growth in high lipid content strains. Biotechnological interventions can make major advances in strain improvement for the commercial scale production of biofuel. We discuss various strategies, including efficient transformation toolbox, to increase lipid accumulation and its quality through the regulation of key enzymes involved in lipid production, by blocking the competing pathways, pyramiding genes, enabling high cell biomass under nutrient-deprived conditions and other environmental stresses, and controlling the upstream regulators of targets, the transcription factors, and microRNAs. We highlight the opportunities emerging from the current progress in the application of genome editing in microalgae for accelerating the strain improvement program.

Exploring the Role of a Cytokinin-Activating Enzyme LONELY GUY in Unicellular Microalga Chlorella variabilis

“…This enzyme has also been characterized in cytokinin activation in other plants such as Medicago truncatula and Solanum lycopersicum , and in certain microbes such as Mycobacterium , Corynebacterium , and Claviceps purpurea ( Eviatar-Ribak et al, 2013 ; Mortier et al, 2014 ; Naseem et al, 2015 ; Samanovic et al, 2015 ; Seo et al, 2016 ). It is known that micro-algae are a good source of feedstock for the biofuel industry ( Stephenson et al, 2011 ), but there is a need for strain improvement to cut production costs ( Sharma et al, 2018 ). Therefore, for strain improvement, the possibility of increasing biomass by overexpressing the cytokinin-activating gene LONELY GUY (LOG) in Chlorella variabilis was explored as previous studies show that exogenous application of cytokinin in microalgae leads to increase in growth rate ( Lu et al, 2014 ).…”

Improving ‘Lipid Productivity’ in Microalgae by Bilateral Enhancement of Biomass and Lipid Contents: A Review

“…Genetic engineering has previously presented a promising approach for research in different scientific areas [30][31][32][33]. As is the case in other research fields, genetic engineering provides an alternative approach to bypass the controversial relationships between lipid accumulation and cell growth [34]. A number of the molecular studies focus on lipid metabolism engineering by over-expression of the enzymes involved in lipid synthesis or suppressing the competitive pathways for enhancing lipid content without comprising the growth rate.…”

Valorization of Wastewater Resources Into Biofuel and Value-Added Products Using Microalgal System

“…The study resulted in a significant increase in biohydrogen yield (65.4 ± 0.3 µmol H 2 L −1 mM −1 acetate) in C. vulgaris culture grown in PBR (Hwang et al, 2018). Recent studies focused on improving the economy of the process through genetic engineering and deploying low-cost photoreactors (Sharma and Arya, 2017;Sharma et al, 2018;Schiano et al, 2019).…”