Improvement of Euglena gracilis Paramylon Production through a Cocultivation Strategy with the Indole-3-Acetic Acid-Producing Bacterium Vibrio natriegens

Abstract

We investigated the putative effects on the growth and paramylon production of <i>Euglena gracilis</i> of cocultivation with <i>Vibrio natriegens</i><i>E. gracilis</i> heterotrophically cocultivated with <i>V. natriegens</i> displayed significant increases in biomass productivity and paramylon content. In addition, the effects of the bacterial inoculum density and the timing of inoculation on the growth of <i>E. gracilis</i> were examined, to determine the optimal conditions for cocultivation. With the optimal deployment of <i>V. natriegens</i>, biomass productivity and paramylon content were increased by more than 20% and 35%, respectively, compared to those in axenic <i>E. gracilis</i> cultures. Interestingly, indole-3-acetic acid biosynthesized by <i>V. natriegens</i> was responsible for these enhancements of <i>E. gracilis</i> The morphology of cocultured <i>E. gracilis</i> cells was assessed. Paramylon granules extracted from the cocultivation were significantly larger than those from axenic culture. Our study showed that screening for appropriate bacteria and subsequent cocultivation with <i>E. gracilis</i> represented an effective way to enhance biomass and metabolite production.<b>IMPORTANCE</b><i>Euglena gracilis</i> has attracted special interest due to its ability to excessively accumulate paramylon. Paramylon is a linear β-1,3-glucan polysaccharide that is the principal polymer for energy storage in <i>E. gracilis</i> The polysaccharide features high bioactive functionality in the immune system. This study explored a new method to enhance the production of paramylon by <i>E. gracilis</i>, through cocultivation with the indole-3-acetic acid-producing bacterium <i>Vibrio natriegens</i> The enhanced production was achieved indirectly with the phytohormone-producing bacteria, instead of direct application of the hormone. The knowledge obtained in this study furthers the understanding of the effects of <i>V. natriegens</i> on the growth and physiology of <i>E. gracilis</i>.