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Background Euglena is a new super health food resource that is rich in the natural polysaccharide paramylon, a linear β-1,3-glucan with various biological activities including activity on the immune system in different cell lines and animals. Despite these reports, the immune regulation mechanism of paramylon is still unclear. Results We investigate the signaling pathways paramylon impacts in immune macrophages. In RAW264.7 macrophages, sonicated and alkalized paramylon oligomers up-regulated inducible nitric oxide synthase (iNOS) and increased secretion of nitric oxide (NO), interleukin (IL)-6 and tumor necrosis factor (TNF)-α, in a concentration-dependent manner. In addition, paramylon activated the nuclear factor-κB(NF-κB) and mitogen-activated protein kinase (MAPK) signaling pathways and inhibiting these pathways attenuated the paramylon-induced secretion of the above immune-mediators. Conclusions These results demonstrate that Euglena gracilis paramylon modulates the immune system via activation of the NF-κB and MAPK signaling pathways and thus has potential therapeutic benefits.

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Heterotrophic cultivation of Chlorella has achieved commercial success, but the application of Chlorella biomass is still limited due to the high cost of biomass production. In this study, an effective and industrially scalable heterotrphic cultivation technology has been developed for a production strain Chlorella sorokiniana GT‐1. Under the optimized culturing conditions, the ultrahigh biomass concentration of 271 and 247 g L−1 was achieved in 7.5 L bench‐scale and 1000 L pilot‐scale fermenters, respectively. Technoeconomic (TE) analysis indicated that the production cost of C. sorokiniana GT‐1 could be reduced to $1601.27 per ton of biomass if the biomass concentration reached 200 g L−1, which is 24.2% lower than that of the reported highest Chlorella biomass production through fermentation with the same TE model. Under the same growth conditions, the maximum biomass concentration of a low‐starch mutant SLM2 was reduced to 93 g L−1, which was 54% lower than that of the wild type, indicating the capabilities of C. sorokiniana GT‐1 cells in accumulating large amounts of starch are essential for achieving the ultrahigh‐cell‐density under the heterotrophic conditions. In addition, the ultrahigh‐cell‐density growth potential of C. sorokiniana GT‐1 cells was inferred to be related to the intrinsic biological characteristics including the tolerance to low dissolved oxygen and a moderate doubling time under the heterotrophic conditions as well. The breakthrough in cultivation technology is promising for Chlorella industry and would expand its applications in food and feed.