Isolation and characterization of a motility-defective mutant ofEuglena gracilis

Abstract

Euglena gracilis is a green photosynthetic microalga that swims using its flagellum. This species has been used as a model organism for over half a century to study its metabolism and the mechanisms of its behavior. The development of mass-cultivation technology has led to E. gracilis application as a feedstock in various products such as foods. Therefore, breeding of E. gracilis has been attempted to improve the productivity of this feedstock for potential industrial applications. For this purpose, a characteristic that preserves the microalgal energy e.g., reduces motility, should be added to the cultivars. The objective of this study was to verify our hypothesis that E. gracilis locomotion-defective mutants are suitable for industrial applications because they save the energy required for locomotion. To test this hypothesis, we screened for E. gracilis mutants from Fe-ion-irradiated cell suspensions and established a mutant strain, ${\mathrm{M}}_{3}^{-}$ZFeL, which shows defects in flagellum formation and locomotion. The mutant strain exhibits a growth rate comparable to that of the wild type when cultured under autotrophic conditions, but had a slightly slower growth under heterotrophic conditions. It also stores 1.6 times the amount of paramylon, a crystal of β-1,3-glucan, under autotrophic culture conditions, and shows a faster sedimentation compared with that of the wild type, because of the deficiency in mobility and probably the high amount of paramylon accumulation. Such characteristics make E. gracilis mutant cells suitable for cost-effective mass cultivation and harvesting.

Dual-frequency impedance assays for intracellular components in microalgal cells

“…5 It is known that sub-cellular functional or morphological defects may lead to abnormal states at the cellular level. [6][7][8] Unfortunately, how cells regulate the size, composition and distribution of intracellular metabolites and organelles is still a long-standing question. 9,10 Therefore, it calls for an efficient detection tool to investigate this basic question.…”

Assessment of the electrical penetration of cell membranes using four-frequency impedance cytometry

“…The detailed components of the CM and KH media were described by Wang et al 35 . Briefly, the CM medium does not include any organic carbon sources, whereas the KH medium contains glucose and various organic acids and amino acids as carbon sources 48 . Both KH and CM media contain high concentrations of inorganic ions, such as Zn 2+ , Mn 2+ , Fe 3+ , Cu 2+ , Co 2+ , and Ni 2+ , some of which can promote the biomass accumulation and multiplication of E. gracilis cells 36,49 .…”

CRISPR/Cas9‐mediated generation of non‐motile mutants to improve the harvesting efficiency of mass‐cultivated Euglena gracilis

“…To improve the harvesting efficiency of E. gracilis , a non‐motile mutant () was generated using Fe‐ion beam irradiation. However, grew slower and produced less lipids than the wild type (WT), suggesting that the mutagenesis caused undesirable side mutations (Muramatsu et al ., 2020). Although flagellar mutants with motility defects have been identified in model organisms such as Chlamydomonas reinhardtii , Trypanosoma brucei and Caenorhabditis elegans (Kamiya et al ., 1991; Wingfield et al ., 2018), a precise manipulation of motility in E. gracilis remains to be explored, despite its industrial usefulness.…”