A novel heterotrophic cultivation process of Euglena gracilis based on NaCl stress significantly increases the paramylon production

The unique paramylon of Euglena gracilis holds significant potential for application in medicine and food. However, there are few reports about increasing the content of paramylon in the process of heterotrophic cultivation of E. gracilis. In this study, a novel method for cultivating E. gracilis through a unique NaCl stressinduced process was developed, resulting in a substantial enhancement in both paramylon content and production. The results of shaking-flask experiments showed that the optimal strategy for NaCl stress was to add 16 g L-1 NaCl for 36 h in the stationary phase. The content of soluble sugar, superoxide dismutase (SOD), peroxidase (POD), and ascorbic acid (AsA) was increased in cells in response to NaCl stress. Subsequently, heterotrophic fedbatch cultivation experiments were conducted in 5 L fermenters. The results showed that adding 16 g L-1 NaCl for 36 h in the heterotrophic culture solution in the stationary phase could increase the content and production of paramylon by 25.33 % and 23.77 %, respectively. The new process of heterotrophic cultivation of E. gracilis developed is simple and easy to operate, which is conducive to scale-up and industrial production of E. gracilis.