Recent Developments on Genetic Engineering of Microalgae for Biofuels and Bio‐Based Chemicals

Abstract

Microalgae serve as a promising source for the production of biofuels and bio-based chemicals. They are superior to terrestrial plants as feedstock in many aspects and their biomass is naturally rich in lipids, carbohydrates, proteins, pigments, and other valuable compounds. Due to the relatively slow growth rate and high cultivation cost of microalgae, to screen efficient and robust microalgal strains as well as genetic modifications of the available strains for further improvement are of urgent demand in the development of microalgae-based biorefinery. In genetic engineering of microalgae, transformation and selection methods are the key steps to accomplish the target gene modification. However, determination of the preferable type and dosage of antibiotics used for transformant selection is usually time-consuming and microalgal-strain-dependent. Therefore, more powerful and efficient techniques should be developed to meet this need. In this review, the conventional and emerging genome-editing tools (e.g., CRISPR-Cas9, TALEN, and ZFN) used in editing the genomes of nuclear, mitochondria, and chloroplast of microalgae are thoroughly surveyed. Although all the techniques mentioned above demonstrate their abilities to perform gene editing and desired phenotype screening, there still need to overcome higher production cost and lower biomass productivity, to achieve efficient production of the desired products in microalgal biorefineries.

Advances and challenges in genetic engineering of microalgae

“…Currently, four main methods have been used for delivery of DNA into the microalgae cells: agitation with glass beads, electroporation, particle bombardment and Agrobacterium construction (Ng et al . ).…”

“…), but the numbers of transformants obtained are relatively low, that is 100 clones per 10 6 cells treated (Ng et al . ).…”

“…Of these two approaches, antibiotic screening is more commonly used due to its simplicity (Ng et al . ), although different species have different susceptibilities to certain antibiotics, and at different concentrations, thus optimization of medium conditions has to be predefined.…”

“…To this end, current engineering technologies of photosynthetic cells need to be upgraded and new tools developed ultimately to produce economically competitive algal sourced biochemicals (Ng et al . ). The metabolic approach or synthetic biology has received the most attention, as the design of a metabolic pathway in a new system opens up possibilities for industrialization of microalgae (Andrianantoandro et al .…”

“…In synthetic biology, the basic gene manipulation process remains the same, including host selection, gene target, plasmid construction, transformation tools, selection system and DNA editing tools (Ng et al . ; Jagadevan et al . ).…”