A Synthetic Biology Perspective on the Bioengineering Tools for an Industrial Microalga: Euglena gracilis

Abstract

Euglena is a genus of single-celled eukaryotes that show both plant- and animal-like characteristics. Euglena gracilis, a model species, is of great academic interest for studying endosymbiosis and chloroplast development. As an industrial species, E. gracilis is also of primary biotechnological and economic importance as high value-added food, medicine, and cosmetic and high-quality feedstock for jet-fuel production because of its cells containing many high-value products, such as vitamins, amino acids, pigments, unsaturated fatty acids, and carbohydrate paramylon, as metabolites. For more than half a century, E. gracilis has been used as an industrial biotechnology platform for fundamental biology research, mainly exploring relevant physiological and biochemical method studies. Although many researchers focused on genetic engineering tools for E. gracilis in recent years, little progress has been achieved because of the lack of high-quality genome information and efficient techniques for genetic operation. This article reviewed the progress of the genetic transformation of E. gracilis, including methods for the delivery of exogenous materials and other advanced biotechnological tools for E. gracilis, such as CRISPR and RNA interference. We hope to provide a reference to improve the research in functional genomics and synthetic biology of Euglena.

Unlocking microalgal host—exploring dark-growing microalgae transformation for sustainable high-value phytochemical production

“…In another study, the use of Agrobacterium transformation for delivery of exogenous materials to Euglena gracilis demonstrated the stability of the mutants for over a year, through 12 rounds of cultivation. In contrast, other transformation methods such as biolistic bombardment, and electroporation techniques lacked stable integration of the transforming DNA into the host genome (Chen et al, 2022).…”

Fast and efficient molecule delivery into Euglena gracilis mediated by cell‐penetrating peptide or dimethyl sulfoxide

“…To date, delivery of exogenous materials into E. gracilis cells can be realized with four methods: Agrobacterium ‐mediated nuclear transformation, electroporation, biolistic bombardment, and single‐cell microinjection [ 5 ]. Although these methods are feasible with appreciable efficiency for E. gracilis transformation, they require sophisticated apparatuses with optimized parameters or take a relatively long time to screen positive clones.…”

High‐throughput sequencing revealed low‐efficacy genome editing using Cas9 RNPs electroporation and single‐celled microinjection provided an alternative to deliver CRISPR reagents into Euglena gracilis

“…However, no mutant could be obtained in the EgGSL2 gene group, even though twelve clones survived. Microinjection is not a newly emerging technique but rather an advanced and sophisticated technique, primarily when performed on cells smaller than 20 μm (Chen et al ., 2022 ). E. gracilis presents sphere‐shaped cells smaller than 20 μm with a flexible pellicle, which hinders manipulation by microinjection.…”