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The Institute of Aquatic Sciences has made progress in the development of algae-derived β-1,3-glucan
2024-12-27 17:49:12
β-1,3-glucan is a kind of active polysaccharide widely distributed in higher plants, bacteria, fungi and algae. It has many functions including improving the body's immunity and is widely used in medicine, health care, food, cosmetics and animal feed industries. Cereals and yeast are the main sources of commercial β-1,3-glucan, but these cell wall-derived β-1,3-glucans have disadvantages such as low content (1-7%), complex extraction process and low water solubility. New β-1,3-glucan resources need to be developed.
The Algal Biotechnology and Bioenergy Center of the Institute of Hydrobiology, Chinese Academy of Sciences took a β-1,3-glucan-rich Malham's Cup Dinocampus as the research object. Through a series of process optimization, the heterotrophic high-density culture and β-1,3-glucan efficient production process of the algae were established. The highest biomass concentration and β-1,3-glucan yield reached 32 and 13.9 g L-1, respectively. On this basis, a purification process for water-soluble β-1,3-glucan was established, and the purity of β-1,3-glucan reached more than 95%. Finally, the activity of golden algae 1,3-glucan was evaluated using the zebrafish tail fin regeneration model. The study found that golden algae β-1,3-glucan has the effect of promoting zebrafish tail fin regeneration and improving the body's antioxidant capacity, and its effect on tail fin regeneration is better than commercial yeast β-1,3-glucan.
This study provides a new way and new resource for producing highly water-soluble bioactive β-1,3-glucan, which is of great significance for promoting the resource utilization of algae β-1,3-glucan (especially golden algae laminarin). The relevant research results were published in Bioresource Technology under the title of High-cell-density cultivation of the flagellate alga Poterioochromonas malhamensis for biomanufacturing the water-soluble β-1,3-glucan with multiple biological activities. The research work was funded by the National Key Research Project Blue Granary Sub-Project, the National Natural Science Foundation of China Youth Project, the Postdoctoral Fund and the Qingdao National Marine Science and Technology Laboratory.
In addition, the team has completed the patent layout around algae species, cultivation processes and active applications, and applied for three related patents.
Abstract
The microalga Poterioochromonas malhamensis was found to be capable of accumulating the storage β-1,3-glucan in soluble form under heterotrophic conditions. In this study, the highest biomass yield of 32.8 g L−1 was achieved by combining the utilization of ammonium chloride as the nitrogen source, simultaneous addition of vitamins B1 and B12 and maintenance of pH at 6.0. Sugar profiling and nuclear magnetic resonance analysis indicated that the P. malhamensis β-1,3-glucan was composed of glucose with the β-(1 → 3) main chain and the β-(1 → 6) side chain. Under the optimal cultivation conditions, the cellular β-1,3-glucan content was up to 55% of the cell dry weight. Moreover, the P. malhamensis β-1,3-glucan could significantly promote the fin regeneration and improve the in vivo antioxidative activity of zebrafish. This study underpins the feasibility of culturing P. malhamensis under heterotrophic conditions for producing the highly water-soluble bioactive β-1,3-glucans for food and pharmaceutical applications.
Introduction
Beta-1,3-glucans are one of the most abundant polysaccharides in bacteria, fungi, algae and plants, which are the carbon storage or structural components of cell walls in these organisms (Wang et al., 2017). They possess a variety of biological activities and functions, including immunomodulation (Suphantharika et al., 2003), antitumor effect (Mo et al., 2017), antioxidation (Xia et al., 2014), lowering serum cholesterol and glucose, and obesity prevention (Bai et al., 2019). Therefore, β-1,3-glucans have been widely used in medicine, food, cosmetic and feed (Zhu et al., 2016).
The global β-glucan market size may achieve more than US$ 700 million in 2025 (Philippini et al., 2019). Cereal and yeast are two main sources of commercial β-1,3-glucans products. However, the contents of cell wall-associated β-1,3-glucans are generally quite low (1–7% of dry weight) in plants and fungi (Lu et al., 2020, Santek et al., 2009). Moreover, most cereal and yeast β-1,3-glucans are partially water-soluble or water-insoluble, and additional physical or chemical modifications are usually required to improve the solubilities of these β-1,3-glucans (Magnani et al., 2009, Zheng et al., 2019). Thus, it is necessary to develop new sources with high content of water-soluble and bioactive β-1,3-glucans.
Microalgae are considered as a potential source for producing β-1,3-glucans (Abu-Ghosh et al., 2021, Jeon et al., 2019). Many microalgae (e.g., Euglenophyta, Bacillariophyta, and Chrysophyta) can produce various β-1,3-glucans with different structures and solubilities. Unlike the cereal and yeast β-1,3-glucans, many microalgal β-1,3-glucans (e.g., chrysolaminarin) are water-soluble, and their cellular contents are much higher (20–50% DW) than that of the cell wall-associated β-1,3-glucans (Barsanti et al., 2001). However, due to the lack of effective technology that can enable high-cell-density cultivation of microalgae, most microalgae with high β-1,3-glucan contents have not been commercially developed. Moreover, bioactivities of the microalgal β-1,3-glucan have been rarely studied.
Poterioochromonas spp. (Chrysophyte), a group of naked unicellular biflagellate algae, was found widely distributed in freshwater (Andersen, 2011). We previously isolated a Poterioochromonas malhamensis and designated it as P. malhamensis CMBB-1 (Ma et al., 2018). Ochromonas, a genus closely-related to Poterioochromonas, was capable of storing water-soluble β-1,3-glucan in the vacuole, which could fill almost the whole volume of the Ochromonas cells (Aaronson and Behrens, 1974). Large vacuoles were also observed in the heterotrophically-grown P. malhamensis CMBB-1 cells. Considering the great potential of P. malhamensis CMBB-1 in converting glucose into β-1,3-glucan under heterotrophic growth, we speculated that it could be a promising bioresource for β-1,3-glucan production.
In this study, the heterotrophically high-cell-density cultivation process of P. malhamensis for producing β-1,3-glucan was established by optimizing culturing conditions including medium pH, vitamin, and nitrogen source type. After extraction and purification treatment, the composition, molecular weight, and structure characteristic of P. malhamensis β-1,3-glucan were analyzed. Finally, the bioactivities of the P. malhamensis β-glucan were evaluated by using a widely applied zebrafish model (Lam and Peterson, 2019, Yang et al., 2019).
Section snippets
Algal strain and culture conditions
The P. malhamensis cells were cultured in seed medium modified according to the previous report (Blom and Pernthaler, 2010), which contained 10.0 g L−1 glucose, 3.0 g L−1 yeast extract, 1.0 g L−1 liver extract powder, 0.5 g L−1 KH2PO4, and 0.5 g L−1 MgSO4·7H2O. To prepare the inoculants for fermentation, the P. malhamensis cells were grown at 28 °C in the dark for four days.
Optimization of culture conditions for β-1,3-glucan production by P. Malhamensis
The batch cultivation was carried out in 1-L fermenter (Applikon Biotechnology, Netherlands) to investigate the effects of
Effects of vitamin and pH on P. malhamensis growth under heterotrophic conditions
The P. malhamensis cells grew slowly in the vitamin-free growth medium, and the cell concentration increases from the initial level of 2.0 × 106 cell mL−1 to 8.5 × 106 cell mL−1 after cultivation for 48 h (Fig. 1A). The addition of VB1 or VB12 alone improved the growth rate of P. malhamensis cells. A better growth-promoting effect was observed when both vitamins were added into the inorganic-nitrogen culture of P. malhamensis, in which the highest cell concentration (2.2 × 107 cell mL−1) was
Conclusions
A heterotrophically high-cell-density cultivation method of P. malhamensis for water-soluble β-1,3-glucan production was established, which achieved the highest biomass of 32.8 g L−1 and β-1,3-glucan yield of 13.9 g L−1. The highly water-soluble P. malhamensis polysaccharide was purified and identified as β-1,3-glucan with the average molecular weight of 16.7 kDa. The P. malhamensis β-1,3-glucan was proved to be effective in promoting the fin regeneration and improving the in vivo antioxidative
CRediT authorship contribution statement
Mingyang Ma: Investigation, Data curation, Formal analysis, Visualization, Writing - review & editing. Yanhua Li: Investigation, Data curation, Formal analysis, Visualization, Writing - review & editing. Jianping Chen: Investigation, Formal analysis. Fuchen Wang: Investigation. Li Yuan: Visualization. Yi Li: Formal analysis. Baocai Zhang: Visualization. Ding Ye: Data curation. Danxiang Han: Conceptualization, Data curation, Writing - review & editing. Hu Jin: Conceptualization, Investigation,
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This study was financially supported by projects from National Key R & D Program of China (No. 2018YFD0901500), National Natural Science Foundation of China (No. 32002413), China Postdoctoral Science Foundation (No. 2019M662749) and Laboratory for Marine Biology and Biotechnology, Pilot National Laboratory for Marine Science and Technology (Qingdao) (MS2019NO03).
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