Hypothesis: the water-insoluble beta glucans within mushrooms that activate the dectin-1b signaling pathway are derived from colonizing yeast

Research supports the theory that the microbiome of plants [1]-[4] and mushrooms [5] produce potent activators of pathogen recognition receptors which are principal contributors to the stimulation of macrophages. We have previously reported [5] that the in vitro macrophage stimulatory activity of water-soluble extracts from 13 different types of edible mushrooms is predominantly due to Toll-like receptor agonists originating from the naturally occurring bacterial communities within these materials. The purpose of the current study was to evaluate whether these 13 types of mushrooms contain water-insoluble beta glucans that activate the dectin-1b signaling pathway. Culinary mushrooms (Agaricus bisporus varieties) were essentially inactive, whereas most of the medicinal mushrooms (Lentinula edodes, Grifola frondosa, Hypsizygus marmoreus varieties, Flammulina velutipes) exhibited potent activation of the dectin-1b signaling pathway. A. bisporus mushrooms with no detectable dectin-1b-dependent activity had yeast colony forming units that were 687 times lower than L. edodes mushrooms exhibiting high activity (half maximal activation values between 6.8 and 11.7 µg/ml). Analysis of 12 commercial batches of L. edodes obtained from different sources indicated that 10 batches exhibited moderate variation (half maximal activation values between 6.6 and 23.1 µg/ml) and 2 batches had minimal or no activity. The two batches that lacked activity were sourced from companies that cultivated the mushrooms in controlled laboratory environments that minimize the growth of microbial organisms. These hypothesis-generating data suggest that the dectin-1b-dependent activity exhibited by these mushrooms is due (at least in part) to the insoluble beta glucans derived from the yeast colonizing these natural products.

• References

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