Anthocyanin extract from Lycium ruthenicum enhanced production of biomass and polysaccharides during submerged fermentation of Agaricus bitorquis (Qu\xe9l.) Sacc. Chaidam

Shan Wu,Hong-Yun Lu,Qi-He Chen,Hui-Chun Xie,Ying-Chun Jiao

doi:10.1007/s00449-021-02605-8

Abstract

Agaricus bitorquis (Quél.) Sacc. Chaidam (ABSC) is a wild edible fungus uniquely found in the Tibet Plateau. ABSC is rich in polysaccharides that are considered biologically active. This study aimed to determine the feasibility of enhancing exopolysaccharide (EPS) production by ABSC in shake flask culture by supplementing the fermentation medium with anthocyanin extract. Different concentrations of Lycium ruthenicum Murr. (LRM) anthocyanin crude extract were tested on ABSC fermentation. The activity of phosphoglucose isomerase (PGI), phosphoglucose mutase (PGM), and phosphomannose isomerase (PMI), enzymes presumably involved in EPS synthesis by ABSC, was determined. ABSC transcriptomic profile in response to the presence of anthocyanins during fermentation was also investigated. LRM anthocyanin crude extract (0.06 mg/mL) was most effective in increasing EPS content and mycelial biomass (by 208.10% and 105.30%, respectively, P < 0.01). The activity of PGI, PGM, and PMI was increased in a medium where LRM anthocyanin extract and its main components (proanthocyanidins and petunia anthocyanin) were added. RNA-Seq analysis showed that 349 genes of ABSC were differentially expressed during fermentation in the medium containing anthocyanin extract of LRM; 93 genes were up-regulated and 256 genes down-regulated. From gene ontology enrichment analysis, differentially expressed genes were mostly assigned to carbohydrate metabolism and signal transduction categories. Collectively, LRM anthocyanins extract positively affected EPS production and mycelial biomass during ABSC fermentation. Our study provides a novel strategy for improving EPS production and mycelial growth during ABSC liquid submerged fermentation.

Highlights

Chaidam (ABSC), commonly known as sand mushroom, is a wild underground edible fungus naturally occurring in the Qaidam Basin, Qinghai Province, China
For morphological observations of mycelial structures, Agaricus bitorquis (Quél.) Sacc. Chaidam (ABSC) mycelium was placed in 250-mL flasks and equal amounts (100 mg) of Lycium ruthenicum Murr. (LRM) anthocyanins and proanthocyanidins (99% purity, Beijing Solarbio Science & Technology Co., Ltd) and petunia anthocyanins (5 mg) (95% purity, SHANGHAI ZZBIO CO., LTD.) were added to each flask, and incubated for 4 days
RNA-Seq libraries were prepared from cDNA generated using iScriptTM cDNA synthesis kit (Bio-Rad, Hercules, CA, USA) at Sangon Biotech (Shanghai, China) and sequenced in an Illumina Hiseq4000 (Illumina Inc., San Diego, CA, USA)

Summary

Introduction

Chaidam (ABSC), commonly known as sand mushroom, is a wild underground edible fungus naturally occurring in the Qaidam Basin, Qinghai Province, China. ABSC usually presents hypertrophied fruiting bodies, low fruiting temperature, and are resistant to a hypoxic environment. ABSC is rich in proteins, minerals, and biologically active compounds, which include polysaccharides, phenolic acids, and terpenes. Extracellular polysaccharides (EPS) of ABSC have demonstrated anti-hypoxia and anti-fatigue properties [1,2,3], making ABSC valuable for potential application in disease prevention and foods. EPS from mushrooms have other health-promoting effects, such as anti-tumor, antiviral, antioxidant, immune regulation, hypoglycemic, and lipid-lowering [4,5,6].

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