Daldinia concentrica

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Classification

a. Higher order taxa

Eukaryota (Domain); Fungi (Kingdom); Dikarya (Subkingdom); Ascomycota (Phylum); Pezizomycotina (Subphylum); Sordariomycetes (Class); Xylariomycetidae (Subclass); Xylariales (Order); Hypoxylaceae (Family); Daldinia (Genus) (1)

2. Description and significance

Daldinia concentrica, commonly referred to as King Alfred’s Mushroom, is an inedible fungus that is known for its hard, shiny, charcoal black hemispherical appearance and banded interior of concentric rings (2). D. concentrica is notable for its role as a saprotroph, a decomposer, found in temperate hardwood forests. This species typically colonizes dead or burnt ash, oak, birch, elm wood, among others (3). As an ascomycete fungus, the asci within the perithecia release ascospores in groups of 8, which are taken by air currents to germinate under favorable conditions. D. concentrica first appears on tree bark as cream-colored patches of spores called conidia, which develop into brown stromata. As the stromata, along with the perithecia for ascospore production, layers form, the fungus matures and develops its characteristic hard, black outer layer on the fruiting body (2).

D. concentrica is of increasing scientific interest due to its synthesis of a wide variety of pharmacologically active secondary metabolites, with antioxidant, cytotoxic, and antiviral effects. These include newly characterized isoindolinones and naphthoquinones with potential anticancer properties, as well as the anti-HIV compound concentricolide (4, 5). Moreover, traditional medicinal uses such as wound healing demonstrate its significance before these novel secondary metabolite discoveries. Currently, the genome of D. concentrica has been sequenced, and information is available about its DNA, along with its morphology and chemistry. However, there is still more to be explored in regards to gene function, regulation, and comparative analysis of its genome and transcriptome, especially for bioactive metabolites of interest. In addition, there is still controversy over the taxonomy of the Daldinia genus, as D. macaronesica, D. martinii, and D. eschscholzii were all found to be separate species from D. concentrica, though they were formerly thought to be varieties of the same species (6). Thus, further genome analysis can also confirm the unique species of D. concentrica from other fungi in the Daldinia genus.

3. Genome structure

To date, the whole genome of Daldinia concentrica has been sequenced. The genome for this species is relatively large in size, containing approximately 37.6 megabases or million base pairs (7). Guanine and cytosine, which are linked by three stabilizing hydrogen bonds, make up around 44% of the fungus’ genome. Although specific data on the number of coding versus non-coding genes remains unavailable, studies highlight that the genome encodes the biosynthesis of unique secondary metabolites. These include metabolites such as Daldinan A and daldinolides A and B (phthalides) which defend fungal cells against oxidative stress (4,8) while others isolated from the genome, like Concentricolide (5) and daldiquinone (naphthoquinone), are responsible for producing antimicrobial properties that show potential in anticancer and anti-HIV research (4,9). Concentricol, a triterpenoid metabolite, functions as a taxonomic marker for D. concentrica, which helps distinguish this species from other fungi (10).

4. Cell structure

During the asexual phase, the fungus grows pink spores known as conidiospores (conidia) (2). Once fruitbodies darken, black, round reproductive spores known as ascospores are released from the openings of the perithecia, which is the primary site of spore production (2). The black color of the fruiting bodies comes from complex pigments that are tightly attached to the cell walls. These pigments form when certain ring- molecules undergo oxidation. The fungus’s vegetative cells are made of septate hyphae that grow densely together to form thick mycelial mats (12). These vegetative and reproductive cell features are used for species identification when DNA sequencing is unavailable.

5. Metabolic processes

D. concentrica is a fungus that obtains nutrients by consuming dead and decaying hardwood, also contributing to the decomposition process. Although no study explicitly classified Daldinia concentrica with a trophic category, it grows on organic plant matter, a clear indicator of a chemoorganoheterotroph (3). Furthermore, it synthesizes several notable bioactive molecules. It contains Dandinan A, a novel isoindolinone compound with strong antioxidant activity, and Daldiquinone, a naphthoquinone that shows anti-angiogenic effects, inhibiting the growth of human endothelial cells with an IC50 of 7.5 µM (4, 8). The species is also known to produce other secondary metabolites, including azaphilone derivatives, triterpenoids, aromatic steroids, and neuroprotective lignans (8). Daldinia concentrica catabolizes carbon substrates like glucose and acetate, using acetate-derived biosynthetic pathways to form aromatic metabolites. Its metabolism involves acetate condensation, similar to fatty acid synthesis, leading to benzene, naphthalene, and quinone derivatives, which are oxidized to form dark perylenequinone pigments and other aromatic compounds (12).

6. Ecology

This fungus inhabits dead or burnt hardwoods such as ash, gorse, oak, and birch. It thrives in temperate forest environments where it contributes to the decomposition of wood material, particularly in areas affected by fire or decay (3). While it has been observed in southern England, the fungus also occurs in the Sirumalai Hills of Tamil Nadu (13). Laboratory studies showed that D. concentrica effectively grew on nutrient-rich media such as malt agar, producing mycelium that darkened with age and formed characteristic pigmented structures. Optimal growth occurs at approximately 30°C, where the fungus produces both vegetative tissue and aromatic metabolites associated with product biosynthesis (12).

7. Pathology

D. concentrica has not been reported to cause disease in humans, animals, or plants. It is a fungus that spreads and breaks down dead wood, especially burned ash trees. D. concentrica does not infect living trees but acts as a decomposer (3). Studies report no evidence of toxicity or infection in humans or animals either; instead, the fungus synthesises bioactive compounds of potential medical interest (4, 13).

8. Current Research

Recent investigations have isolated and structurally characterized new metabolites from D. concentrica , expanding knowledge of its chemical biodiversity. ive previously unknown metabolites, daldinans B and C, daldinolides A and B, and daldiquinone, along with two known compounds, were isolated from the fruiting bodies of Daldinia concentrica. Among these, daldiquinone was identified as a cytotoxic agent that inhibits endothelial cell proliferation, guiding further research into the anticancer and antimicrobial potential of Daldinia metabolites (4). More recent research on D. concentrica has included broader phytochemical screening, revealing the presence of tannins, saponins, flavonoids, and phenolic compounds, which reinforce its overall chemical diversity and potential applications in treating infections, inflammation, and cancer (14). Additionally, wound healing activity of D. concentrica methanolic extracts has been experimentally validated in rat models, supporting traditional medicinal use, though acknowledging slower efficacy compared to commercial antibiotics (13).

References

(1) Schoch, C. L., et al. (2020). NCBI Taxonomy: A comprehensive update on curation, resources and tools. Database (Oxford), 2020, baaa062. https://doi.org/10.1093/database/baaa062.

(2) Elliott, J. S. B. (1917). On the formation of conidia and the growth of the stroma of Daldinia concentrica. Transactions of the British Mycological Society, 6(4), 269–IN7. https://doi.org/10.1016/S0007-1536(17)80039-5.

(3) Hingley, M. R. (1971). The Ascomycete Fungus, Daldinia concentrica as a Habitat for Animals. The Journal of Animal Ecology, 40(1), 17. https://doi.org/10.2307/3327.

(4) Kamauchi, H., Shiraishi, Y., Kojima, A., Kawazoe, N., Kinoshita, K., & Koyama, K. (2018). Isoindolinones, Phthalides, and a Naphthoquinone from the Fruiting Body of Daldinia concentrica. Journal of Natural Products, 81(5), 1290–1294. https://doi.org/10.1021/acs.jnatprod.7b00976.

(5) Qin, X.-D., Dong, Z.-J., Liu, J.-K., Yang, L.-M., Wang, R.-R., Zheng, Y.-T., Lu, Y., Wu, Y.-S., & Zheng, Q.-T. (2006). Concentricolide, an Anti-HIV Agent from the Ascomycete Daldinia concentrica. Helvetica Chimica Acta, 89(1), 127–133. https://doi.org/10.1002/hlca.200690004.

(6) Stadler, M., Wollweber, H., Jäger, W., Briegert, M., Venturella, G., Castro, J. M., & Tichy, H.-V. (2004). Cryptic species related to Daldinia concentrica and D. eschscholzii, with notes on D. bakeri. Mycological Research, 108(3), 257–273. https://doi.org/10.1017/s0953756204009335.

(7) Wibberg, D., Stadler, M., Lambert, C. et al. High quality genome sequences of thirteen Hypoxylaceae (Ascomycota) strengthen the phylogenetic family backbone and enable the discovery of new taxa. Fungal Diversity 106, 7–28 (2021). https://doi.org/10.1007/s13225-020-00447-5.

(8) Lee, I.-K., Kim, S.-E., Yeom, J.-H., Ki, D.-W., Lee, M.-S., Song, J.-G., Kim, Y.-S., Seok,S.-J., & Yun, B.-S. (2011). Daldinan A, a novel isoindolinone antioxidant from the ascomycete Daldinia concentrica. The Journal of Antibiotics, 65(2), 95–97. https://doi.org/10.1038/ja.2011.109.

(9) Quang, D. N., Hashimoto, T., Tanaka, M., Baumgartner, M., Stadler, M., & Asakawa, Y. (2002). Chemical Constituents of the Ascomycete Daldinia concentrica. Journal of Natural Products, 65(12), 1869–1874. https://doi.org/10.1021/np020301h.

(10) Stadler, M., Baumgartner, M., Grothe, T., Mühlbauer, A., Seip, S., & Wollweber, H. (2001). Concentricol, a taxonomically significant triterpenoid from Daldinia concentrica. Phytochemistry, 56(8), 787–793. https://doi.org/10.1016/s0031-9422(01)00032-2.

(11) Sharland, P. R., & Rayner, A. D. M. (1986). Mycelial interactions in Daldinia concentrica. Transactions of the British Mycological Society, 86(4), 643–649. https://doi.org/10.1016/S0007-1536(86)80068-7.

(12) Allport, D. C. & Bu’Lock, J. D. (1960). 134. Biosynthetic pathways in Daldinia concentrica. Journal of the Chemical Society (Resumed), 654. https://doi.org/10.1039/jr9600000654.

(13) Rajeshwaran Thangaraj, Raj, S., & Kumuthakalavalli Renganathan. (2017). WOUND HEALING EFFECT OF KING ALFERD’S MUSHROOM (DALDINIA CONCENTRICA) USED BY TRIBES OF SIRUMALAI HILLS, TAMILNADU, INDIA. International Journal of Pharmacy and Pharmaceutical Sciences, 9(7), 161–161. https://doi.org/10.22159/ijpps.2017v9i7.20628.

(14) Thakur, K., Roy, B. C., Saradar, B., Sahu, B. K., Marndi, S., Kumar, S., & Das, A. (2024). Prediction of medicinal values of Daldinia concentrica: A wild mushroom of India. In Edible and medicinal mushrooms of India (Vol. 2, pp. 38–45). https://doi.org/10.5281/zenodo.14551401.

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Edited by Maanya Baranwal, Sumaira Haque, Ava Milner, Arianna Acosta, and Anjanie Hansraj, students of Jennifer Bhatnagar for [http://www.bu.edu/academics/cas/courses/cas-bi-311/ BI 311 General Microbiology], 2025, Boston University.