Laetiporus sulphureus
1. Classification
a. Higher order taxa
Domain: Eukarya; Kingdom: Fungi; Phylum: Basidiomycota; Class: Agaricomycetes; Order: Polyporales; Family: Laetiporaceae; Genus: Laetiporous; Species: Laetiporus sulphureus [1]
2. Description and significance
Laetiporus sulphureus is a parasitic fungus found on every continent other than Antarctica, growing most abundantly from May to October on various deciduous and coniferous trees; the fruiting body grows from the heartwood of its host tree, leading to heart rot disease and ultimately killing the host [2,3]. L. sulphureus, commonly known as “chicken of the woods,” is an edible mushroom incorporated into various international cuisines [2]. Furthermore, L. sulphureus offers several potential benefits to human health; current research indicates potential antioxidant and antimicrobial effects [4,5].
3. Genome structure
L. sulphureus was sequenced in 2022, showing a 37.4 Gbp genome organized into 14 linear chromosomes. A G:C content of 50.2-52.4% indicates a stable genomic structure capable of withstanding higher temperatures before denaturation [6]. Similarly, a 2018 study used Illumina sequencing to characterize the L. sulphureus mitochondrial genome (mitogenome), highlighting its 101 kbp, circular DNA composition. The observed alignment of nuclear and mitochondrial DNA potentially indicates several instances of gene transfer. Additionally, genomic analysis clarifies the identification of phylogenetic groups. When comparing the mitogenome against other fungi in the order Polyporales, 11 of the 15 common protein families identified in L. sulphureus had unique sequence lengths and displayed a high degree of conservation, indicating a possible early separation from other Polyporales [7]. L. sulphureus taxa found in different geographical regions exhibit genetic variation; a 2009 study used nuclear rRNA internal transcribed noncoding regions (ITS) to categorize closely related Laetiporus into clusters, uncovering eight new species, each expressing differences in pigmentation, chemical composition, and growth rates. The significance of these findings suggests that differing subspecies of L. sulphureus may incur various benefits and drawbacks, but there is not enough evidence to establish any definitive health claims [8]. In a study released in 2020, researchers identified a gene responsible for producing antifungal compounds. The gene LpaA produces polyene synthase, an enzyme capable of producing a variety of acids that seem to affect the ability of fungal protoplasts, the fungal life stage where it prepares to merge with others to form a diploid, to survive and reproduce [9].
4. Cell structure
L. sulphureus is multicellular and grows in semi-circular shelves projecting from the sides of trees. Shelves of L. sulphureus tend to grow stacked on top of one another in large clusters [2]. L. sulphureus presents with a bright yellow or orange pigment, similar to the color of elemental sulfur [10]. Spores produced by L. sulphureus are elliptical or ovular in shape, with a length ranging between five and eight microns [6]. Inside the host tree, fungal vegetative cells grow into long, string-like projections called hyphae. The hyphae absorb nutrients from the host tree to be transported to the fungal body and metabolized [6].
5. Metabolic processes
Although L. sulphureus possesses much of the same metabolic processes as seen in other fungi, such as fermentation and aerobic respiration, the metabolic byproducts produced by this species have garnered interest within the scientific community for possible applications. L. sulphureus contains high amounts of minerals that support human health, including potassium, calcium, magnesium, and phosphorus [11]. In addition, multiple studies have found L. sulphureus to contain polysaccharides with antioxidant properties [10]. In a study released in 2020, researchers identified a gene responsible for the production of antifungal compounds. The gene LpaA produces polyene synthase, an enzyme capable of producing a variety of acids that seem to affect the ability of fungal protoplasts (i.e., the fungal life stage where it prepares to merge with others to form a diploid) to survive and reproduce. The ability to disrupt growth was also observed with insect larvae, indicating that different acidic products may target specific species that could compete with L. sulphureus for resources [9]. A separate study from 2021 identified the same class of acidic compounds in the digestion pathway for L. sulphureus. L. sulphureus acts as a saprotroph and opportunistic parasite (e.g., growing from damaged bark via cellulose digestion) [12]. While the macro digestion seems to be done similarly to other brown-rot fungi, where it infects the trees’ wood lattice and introduces cellulose-digesting enzymes, the acids perform final breakdown before absorption. These findings potentially indicate the pathway the organisms developed for self-defense and sequestration from digestion [13]. Additionally, L. sulphureus similarly synthesizes a class of hemolysin proteins previously identified to be produced by C. perfringens. These toxins puncture holes in Gram-negative bacteria, serving as an avenue for anti-microbial innate immunity [14].
6. Ecology
L. sulphureus has an ambiguous ecological role; it acts as both a saprotroph, though cases have been reported of opportunistic parasitism when growing from damaged bark [12]. The chicken of the woods, the organism’s common name, is classified broadly as a brown-rot fungus, meaning it is a saprotroph that decomposes trees. Unlike white-rot fungi, which decompose wood lignin, this taxa decompose cellulose and minimally distorts lignin to achieve its goal, generating its brown-rot appearance [13]. L. sulphureus is typically found in hardwood forests across North America, with a distinct growth preference for oak trees [15].
7. Pathology
L. sulphureus is safe for human consumption and is incorporated into multiple international culinary traditions if harvested from growths on trees that shed their leaves annually [16]. However, if harvested from coniferous trees, L. sulphureus may contain the toxins from those trees, which are harmful to humans [16]. The growth stage must also be accounted for when harvesting, as older growths may contribute to adverse side effects; there have been instances where individuals reported vomiting and muscle cramps, likely due to the older fungus contributing to indigestion [16]. Additional adverse side effects of L. sulphureus are related to the misidentification of the fungus and accidental consumption of L. huroniensis and L. gilbertsonii [17]. As of 2015, researchers identified several compounds found in L. sulphureus that are toxic to humans; yet, due to their dilute concentration, no adverse health effects were attributed to them [3].
8. Current Research
Medical
Recent studies have shown that the extracts of L. sulphureus contain anti-cancer compounds. In a 2023 study, researchers isolated the phenolic compounds (i.e., compounds with antioxidant properties) present in L. sulphureus via ethanolic extraction to determine their cytotoxic effects on cervical and colorectal cancer cells [18]. The investigators did not observe high cytotoxicity of the L. sulphureus extract, as was seen in a 2016 research study using immortal cancer cells and a different L. sulphureus extract; however, they noted a decrease in cancer cell proliferation and metastasis resulting from the extract’s recruitment of radical oxygen species, elucidating how the bioactive properties of L. sulphureus contribute to its potential therapeutic use against cancers [4,18].
Research using phenolic compound-containing extracts from L. sulphureus has explored the antimicrobial properties of the fungus [4,18,19]. In a 2016 study, researchers investigated the effects of L. sulphureus extracts on Helicobacter pylori, a common pathogenic Gram-negative bacteria [4]. Researchers found that methanol extracts containing large amounts of polyphenols antagonized H. pylori growth and exhibited antimicrobial effects against ten other bacterial strains [4]. The anti-cancer and antimicrobial properties of L. sulphureus demonstrate how the fungus can treat various diseases and pathogens, probing researchers to be interested in L. sulphureus genetic composition [20].
Culinary
L. sulphureus is a staple food in many international cultures for its nutritional value and taste [2]. Furthermore, other than its historical medicinal uses, there has been significant development in research to make the chicken of the woods a functional food in the modern-day diet. Current evidence suggests that L. sulphureus has the macro- and micronutrient components of well-balanced food, that is, 64.9% carbohydrates, 11.9% proteins and essential amino acids, 5.9% fatty acids, fiber, minerals, and vitamins [2,17]. At 360 kcal/100 g, L. sulphureus exudes potential to the modern diet. Today, we find chicken of the woods in restaurants, grocery stores, and new recipes [17].
9. References
[1] Schoch CL, et al. NCBI Taxonomy: a comprehensive update on curation, resources and tools. Database (Oxford). 2020: baaa062. PubMed: 32761142 PMC: PMC7408187.
[2] Khatua, S., Ghosh, S., & Acharya, K. (2017). Laetiporus sulphureus (Bull.: Fr.) Murr. as Food as Medicine. Pharmacognosy Journal 9(6), 1-15.
[3] Alquini, G., Carbonero, E. R., Rosado, F. R., Cosentino, C., & Iacomini, M. (2004). Polysaccharides from the fruit bodies of the basidiomycete Laetiporus sulphureus (Bull.: Fr.) Murr. FEMS Microbiology Letters 230(1), 47–52.
[4] Kolundžić, M. D., Grozdanić, N., Stanojković, T. P., Milenković, M. T., Dinić, M. R., Golić, N. E., Kundaković, T. D. (2016). Antimicrobial and cytotoxic activities of the sulphur shelf medicinal mushroom Laetiporus sulphureus (Agaricomycetes) from Serbia. International Journal of Medicinal Mushrooms 18(6), 469–476.
[5] Turkoglu, A., Duru, M. E., Mercan, N., Kivrak, I., & Gezer, K. (2007). Antioxidant and antimicrobial activities of Laetiporus sulphureus (Bull.) Murrill. Food Chemistry, 101(1), 267–273.
[6] Wright, R., Woof, K., Douglas, B. & Gaya, E. (2022). The genome sequence of the chicken of the woods fungus, Laetiporus sulphureus (bull.) Murrill, 1920. Wellcome Open Research 7, 83.
[7] Li, Q. et al. (2018). Characterization and phylogenetic analysis of the complete mitochondrial genome of the medicinal fungus Laetiporus sulphureus. Scientific Reports 8.
[8] Vasaitis, R. et al. (2009). Genetic variation and relationships in Laetiporus sulphureus S. lat., as determined by its rdna sequences and in vitro growth rate. Mycological Research 113, 326–336.
[9] Seibold, P. S., Lenz, C., Gressler, M. & Hoffmeister, D. (2020). The laetiporus polyketide synthase lpaa produces a series of antifungal polyenes. The Journal of Antibiotics 73, 711–720.
[10] Klaus, A. et al. (2013). The edible mushroom Laetiporus sulphureus as potential source of natural antioxidants. International Journal of Food Sciences and Nutrition 64, 599–610.
[11]Kovács, D., & Vetter, J. (2015). Chemical composition of the mushroom Laetiporus sulphureus (bull.) murill. Acta Alimentaria 44(1), 104–110. [12] Abdel-Hamid, A. M., Solbiati, J. O. & Cann, I. K. O. (2013). Insights into lignin degradation and its potential industrial applications. Advances in Applied Microbiology 1–28. doi:10.1016/b978-0-12-407679-2.00001-6
[13] Langer, G. J., Bußkamp, J., Terhonen, E. & Blumenstein, K. (2021). Fungi inhabiting woody tree tissues. Forest Microbiology 175–205. doi:10.1016/b978-0-12-822542-4.00012-7
[14] Nagahama, M., Oda, M., Tsuge, H., Kobayashi, K. (2014). Enteric toxins of clostridium perfringens: Beta toxin, TpeL, epsilon toxin and iota toxin. Molecular Medical Microbiology (Second Edition). [15] Banic, M. T., Burdsall, H. H. & Volk, T. J. Identification of groups within Laetiporus sulphureus in the United States based on RFLP analysis of the nuclear ribosomal DNA. Folia Cryptogamica Estonica 33, 9–14 (1998). [16] Adamska, I. (2023). The possibility of using sulphur shelf fungus (Laetiporus sulphureus) in the food industry and in Medicine-A Review. Foods 12(7), 1539.
[17] Jiri, P. (2019). Will the sulphur polypore (Laetiporus sulphureus) become a new functional food? Global Journal of Medical and Clinical Case Reports 6(1), 006–009. https://doi.org/10.17352/2455-5282.000068
[18] Jovanović, M. M., Marković, K. G., Grujović, M., Pavić, J., Mitić, M., Nikolić, J., & Šeklić, D. (2023). Anticancer assessment and antibiofilm potential of Laetiporus sulphureus mushroom originated from Serbia. Food Science and Nutrition 10(11), 6393-6402. doi:10.1002/fsn3.3577
[19] Dong, W., Wang, Z., Feng, X., Zhang, R., Shen, D., Du, S., … Qi, J. (2022). Chromosome-level genome sequences, comparative genomic analyses, and secondary-metabolite biosynthesis evaluation of the medicinal edible mushroom Laetiporus sulphureus. Microbiology Spectrum 10(5). doi:10.1128/spectrum.02439-22
[20] Bulam, S., Üstün, N. Ş. & Pekşen, A. (2019). Nutraceutical and food preserving importance of Laetiporus sulphureus. Turkish Journal of Agriculture - Food Science and Technology 7, 94–100.
Edited by [Felipe Adelmann Brants, Maya Rice, Brad Malicki, Bianca Frintu, and Noah Barrow], students of Jennifer Bhatnagar for BI 311 General Microbiology, 2023, Boston University.
