Cultivation properties and cell morphology of the <i>Euglena gracilis</i> SM-ZK strain under fed-batch cultivation conditions

Euglena gracilis cells grown in the dark accumulate a β-1,3-glucan called paramylon, synthesized from organic carbon sources. Paramylon has potential applications as a raw material for bioplastics and nanofibers. Strain SM-ZK, a streptomycin-bleached mutant of E. gracilis, lacks chloroplasts permanently and accumulates more paramylon than the wild-type strain. However, data are limited on the fermentation characteristics of this mutant strain. This study compares the cultivation characteristics of E. gracilis strains Z (wild-type strain) and SM-ZK under fed-batch cultivation conditions. Strain SM-ZK showed significantly higher productivity in terms of both biomass yield and glucose consumption than strain Z. Moreover, strain SM-ZK cells appeared to be gradually enlarged during fed-batch cultivation compared with strain Z that grows in uniform sizes. These novel findings support the potential use of strain SM-ZK for industrial-scale production of paramylon.