Scientific Reports (May 2023)

New insights into raceway cultivation of Euglena gracilis under long-term semi-continuous nitrogen starvation

  • Ranjith Kumar Bakku,
  • Yoshimasa Yamamoto,
  • Yu Inaba,
  • Taro Hiranuma,
  • Enrico Gianino,
  • Lawi Amarianto,
  • Waleed Mahrous,
  • Hideyuki Suzuki,
  • Kengo Suzuki

DOI
https://doi.org/10.1038/s41598-023-34164-1
Journal volume & issue
Vol. 13, no. 1
pp. 1 – 11

Abstract

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Abstract This study aimed to investigate the physiological responses of Euglena gracilis (E. gracilis) when subjected to semicontinuous N-starvation (N−) for an extended period in open ponds. The results indicated that the growth rates of E. gracilis under the N− condition (11 ± 3.3 g m−2 d−1) were higher by 23% compared to the N-sufficient (N+, 8.9 ± 2.8 g m−2 d−1) condition. Furthermore, the paramylon content of E.gracilis was above 40% (w/w) of dry biomass in N− condition compared to N+ (7%) condition. Interestingly, E. gracilis exhibited similar cell numbers regardless of nitrogen concentrations after a certain time point. Additionally, it demonstrated relatively smaller cell size over time, and unaffected photosynthetic apparatus under N− condition. These findings suggest that there is a tradeoff between cell growth and photosynthesis in E. gracilis, as it adapts to semi-continuous N− conditions without a decrease in its growth rate and paramylon productivity. Notably, to the author’s knowledge, this is the only study reporting high biomass and product accumulation by a wild-type E. gracilis strain under N− conditions. This newly identified long-term adaptation ability of E. gracilis may offer a promising direction for the algal industry to achieve high productivity without relying on genetically modified organisms.