Water-soluble β-glucan from G. lucidum as a potential functional food ingredient with gut microbiota-regulating and immune-enhancing activities.

Ganoderma lucidum is a nutraceutical and a traditional medicinal mushroom. β-glucans are the predominant bioactive components in G. lucidum. The molecular weight of β-glucan extracted from G. lucidum by using traditional method is too high, resulting in low solubility and low biological activity. In this study, we obtain a soluble and homogeneous branched β-glucan with (1 → 3)-linked backbone and (1 → 6)-linked side chains (named GLP-D) by using membrane filtration and ultrasonic degradation. GLP-D has simple structures, which is easy for the quality control in future production. GLP-D showed a significant protective effect against cyclophosphamide-induced suppression of lymphocyte proliferation. When gut microbiota was depleted via antibiotic treatment, GLP-D-induced enhancement of splenic lymphocyte proliferation was significantly abrogated. Further, using streptomycin treatment and in vitro fluorescence-activated cell sorting (FACS), we identified Lactobacillus and Alistipes as the bacterium potentially responsible for the effects of GLP-D. GLP-D may be serving as a novel prebiotic which is beneficial for immunocompromised individuals. These findings are crucial to the utilization of G. lucidum.