Hericium erinaceus

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1. Classification

a. Higher order taxa

Hericium erinaceus is classified under the domain Eukaryota, kingdom Fungi, phylum Basidiomycetes, class Agaricomycetes, order Russulales, and family Hericiaceae [1].

2. Description and significance

Hericium erinaceus is an edible mushroom also named “Bearded Tooth Fungus,” “Lion’s Mane Mushroom,” or “Yamabushitake" for its unique macromorphology [2]. In addition to its culinary use, H. erinaceus has been prescribed as an alternative natural remedy for epigastric pain and general weakness or fatigue in traditional medicine across Asia for centuries [3,2]. The fruiting body and mycelium of H. erinaceus contain around 70 structurally different secondary metabolites [4]. Each of these compounds potentially produce various bioactive effects including antibiotic, anticarcinogenic, neuroprotective, anti-inflammatory, immunostimulatory, and antioxidative properties among others [4]. The discovery of these effects has expanded the usage of H. erinaceus across various medical specialties. Ongoing research focuses on extracting these compounds to elucidate their mechanisms of action, which are largely unknown, and thus their therapeutic potential as pharmaceutical agents for treating or curing neurological conditions, gastrointestinal disorders, and cancer [2].

3. Genome structure

The genome of H. erinaceus is 41.2 Mb in size with 10,620 predicted genes and 447 transcription factors [5]. 44.2% of the genome sequence contains protein-coding genes. Repeat sequences, or short/long patterns of DNA that can occur, account for 19.0% of the genome; tandem repeats make up 1.7% of the genome; and transposable elements account for 17.3% of the genome [5]. 341 genes encoding Carbohydrate-active enzymes (CAZymes), which build and break down complex carbohydrates and glycoconjugates, were found in the genome of H. erinaceus [5, 6]. Of the 341 CAZyme genes found, 161 encode glycoside hydrolases, 59 encode glycosyl transferases, 7 encode polysaccharide lyases, 26 encode carbohydrate esterases, 4 encode carbohydrate-binding modules, and 84 encode auxiliary activities enzymes [5]. Glycoside hydrolases that are required to digest cellulose and hemicellulose were also found in the H. erinaceus genome [5].

4. Cell structure

The cell wall of H. erinaceus is mainly made up of low molecular mass polysaccharides that are water soluble and alkali-soluble [7]. The water soluble polysaccharides are mainly made up of glucose and galactose. H. erinaceus also has numerous polysaccharide-protein complexes that promote its medicinal properties [7]. The spores of H. erinaceus are ellipsoid and smooth to slightly roughened. The spores of H. erinaceus have an average size of 5.5 -- 7 × 4.5 -- 5.5 μm [8] .

5. Metabolic processes

H. erinaceus contains a large percentage of polysaccharides, specifically in its cell wall. These polysaccharides act as the main bioactive compound that lend the mushroom to being beneficial to the medical and healthcare industries [7]. Furthermore, H. erinaceus contains a large variety of secondary metabolites, which can be loosely classed by characteristics of organic structure: erinacines, hericerins (aromatic compounds), glycoproteins, polysaccharides, and sterols [4]. Carbohydrate metabolism pathways – carbon metabolism, pyruvate metabolism, and glycolysis and gluconeogenesis – in two mutant strains (HEB and HEC) of H. erinaceus with higher polysaccharide production, as well as a cAMP-PKA pathway, are upregulated such that glucose availability can be used efficiently in order to promote cell growth and division [9]. Cytochrome P450 proteins are highly active in H. erinaceus and have been found to play a large role in secondary metabolite biosynthesis, amino acid transport, and energy production in the mushroom [10]. H. erinaceus’s increased polysaccharide synthesis, carbohydrate metabolism, and glucose signaling, are the properties of interest in the medical community.

6. Ecology

H. erinaceus is a fungus with a mature fruiting body: a bulbous structure hidden by smooth fibrous spines dangling from the body in a radiating arrangement [2]. Generally, the spines’ characteristics vary with maturation. An immature specimen has white spines that are 1 cm or less in length, whereas a fully developed specimen’s spines are 1-4 cm and may discolor into a yellow-brown color [11]. H. erinaceus most often grows in Japan, North America, and the UK. Though overall, H. erinaceus is not common in nature, it is typically found growing from wood in sparsely populated forests with older trees [12]. It most often grows in dead wood, but also sometimes grows out of knotholes in trees or cracks in the bark of living trees. The growth of H. erinaceus indicates that it is a saprotroph, using already decaying wood as its source of nutrition rather than acting as the cause of disease in the wood [12]. It is most abundant in the northern hemisphere from the months of September to December ["#References2]. 'H. erinaceus' is beginning to disappear from natural habitats, perhaps indicating extinction [2].

7. Pathology

How does this organism cause disease? Human, animal, plant hosts? Virulence factors, as well as patient symptoms.

8. Current Research

Include information about how this microbe (or related microbes) are currently being studied and for what purpose

9. References

[1] [Schoch, C. L., Ciufo, S., Domrachev, M., Hotton, C. L., Kannan, S., Khovanskaya, R., Leipe, D., Mcveigh, R., O’Neill, K., Robbertse, B., Sharma, S., Soussov, V., Sullivan, J. P., Sun, L., Turner, S., & Karsch-Mizrachi, I. (2020). Taxonomy browser (Hericium erinaceus). National Center for Biotechnology Information. https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=91752] [2] [Thongbai, B., Rapior, S., Hyde, K.D., Wittstein, K., & Stadler, M. (2015). Hericium erinaceus, an amazing medicinal mushroom. Mycol Progress, 14, 91. https://doi.org/10.1007/s11557-015-1105-4]