Auricularia auricula-judae
1. Classification
a. Higher order taxa
Domain: Eukaryota, Phylum: Basidiomycota, Class: Agaricomycetes, Order: Auriculariales, Family: Auriculariaceae, Genus: Auricularia Include this section if your Wiki page focuses on a specific taxon/group of organisms
2. Description and significance
Auricularia auricula-judae is a fungus found in various parts of the globe, with cultural significance in both the western and eastern hemispheres. It thrives the best in temperate climates and its physical appearance resembles a brown-black color folded around itself in the shape of an ear and its common name is often referred to as the Judas’s Ear.
A. auricula-judae is commonly consumed in the diet of eastern asian cuisines, and has a rich historic and cultural significance for asian countries, particularly in China (1). A. auricula-judae is known to have medicinal properties and has been used for many years as a treatment in ancient chinese medicine (2) including controlling the intestinal system, treatment for cardiovascular disorder, and slowing down the aging process (3). It’s main active ingredient, Auricularia auricula polysaccharide (AAP), constitutes 60% of the fungus’s total content, and research on this organic component has intensified due to their numerous therapeutic effects on various chronic disorders such as cancer, type 2 diabetes, and obesity (1).
With AAP’s prominent use in research, scientists are still trying to identify extraction methods with high yield, precision, and reproducibility in extracted AAP molecular weight and structure as a means to resolve the current lack of standardization in methodology (3).
Additionally, A. auricula-judae cultivation has an immense economic impact on China, outputting a value of 37.46 billion yuan from mushroom production (4). In general, the growth and development of A. auricula-judae has had far-reaching impacts on multiple sectors ranging from agriculture to food, health, and the commercial sawdust industry (4).
3. Genome structure
A. auricula-judae has a complete nuclear ribosomal DNA gene complex of 49.76 Mb (5). There are a total of 16,244 coding sequence genes in which every coding sequence gene has an average length of 1355.30 bp. There exist 87,130 exons and 70,886 introns with an average length of 252.67 bp for exons and 98.18 bp for introns. The GC content is around 57% and there are a total of 16,244 protein-encoding genes in which each protein-encoding gene averages around 1355.30 bp. There are a total of 150 tRNAs, 34 snRNAs, and 11 rRNAs in which 12 tRNAs are pseudogenes and the other 138 are anticodon tRNAs that correspond to the 20 common amino acid’s codons. Furthermore, 1801 proteins are categorized as COG (Clusters of Orthologous Genes) while 408 are categorized as proteins for “general functions” .
Furthermore, previous research was able to identify the rDNA gene complex which has been separated into the 28S, 18S, and 5.8S regions (6). These rDNA genes as well as the ITS and IGS regions (spacer DNA sequences that separate the small and large rRNA genes) have been used in phylogeny studies to understand the evolutionary relationships A. auricula-judae have with other organisms. The exact number of base pairs for each region were identified: 1805 bp in 18S rDNA; 513 bp in ITS, 5.8S, and ITS2; 3135 bp in 28S; 2335 bp in IGS1; 118 bp in 5S; and 3304 bp in IGS2. There are no repeated sequences between the IGS1 and IGS2 regions. It was also identified to be G-rich at nucleotides between 8551 bp and 8638 bp .
Recent discoveries on genetic differences between Chinese A. auricula-judae and its European counterpart have resulted in the reclassification of Chinese A. auricula-judae as its separate species: A. auricula-heimuer (7). Furthermore, through Next-Generation Sequencing (NGS), 17 simple sequence repeat (SSR) markers in A. auricula-judae were found, which enables mushroom cultivated variations (cultivars) to be differentiated (8). This is especially helpful because differentiating mushroom cultivars has been a major issue in China that hindered the productivity and precision in mushroom farming.
4. Cell structure
A. auricula-judae has a thick basidiomata, a club shaped fleshy spore-producing flesh with a color range spanning from reddish brown to white (9). It is well known for its distinguishing features such as its tinted brown ear shape. In its earlier stages, its physical features are gelatinous, pliant, and brown, which turns to a harder black color as it matures. A. auricula-judae also has three major cultivars in China—Wujin (smooth), Banjin (partially wrinkled), and Quanjin (fully wrinkled)—that differ by their surface wrinkles (also known as veins), which are thought to be one of the major features of fruiting bodies (10).
A. auricula-judae can be found in groups or alone and the length of stems varies, and the typical size of one fungi is usually around 9 cm wide and 1-3 mm thick when it's fresh. The large basidia is known to produce its reproductive spores known as basidiospores (9). Near the basidia, there are little crystals scattered around the hymenium, as well as tiny hairs. The hairs are clear and thick, with the length around around 300–500 × 1–2 µm (8). The hyphae are connected through clamp connections,which are hook-like structures formed by growing hyphal cells. The basidiospores are clear in coloration, with a smooth surface as well as a rod-like structure. The size varies but usually around the length of 7-14 µm and width of 5-7 µm (8).
5. Metabolic processes
A. auricula-judae is a saprotrophic organism, meaning that it grows on rotted wood such as dead trees or fallen branches as it eats decaying organic matter (11). It directly digests and absorbs nutrients through the breakdown of the organic matter it decomposes (12), making it a chemoorganoheterotroph and a decomposer.
6. Ecology
A. auricula-judae originates from China, where it is commonly found growing on decaying trees in the mountainside (4). They can be found growing in singlets or clusters on coniferous and deciduous wood, as it is a wood-decaying fungus. The optimal growth conditions for this fungus is around a temperature of 25~30°C and a pH level of 6~7 (2). In terms of cultivation, A. auricula-judae is primarily farmed in temperate regions that provide these optimal conditions such as Asia, where it is also high in demand for medicinal and culinary purposes.
7. Pathology
A. auricula-judae has not been found to be pathogenic to humans. Despite the trace amounts of hydrogen cyanide, there has not been any toxic elements found in this fungus and no evidence pointing towards lethal or adverse effects from A. auricula-judae consumption (13). Contrarily, it contains antimicrobial effects that counter multiple human bacterial pathogens, as well as two fungal isolates (4). Its proteins may potentially serve as antimicrobial protein/peptides in treating human bacterial and fungal infections. Consumption of A. auricula-judae polysaccharides (AAP) supplements have therapeutic effects on type II diabetes, down-regulating harmful cholesterol (LDLs), while up-regulating helpful cholesterol (HDLs) (14). AAP supplementation is associated with enhanced phosphorylation of AKT and AMPK, suggesting a regulatory role of AAPs in glucose metabolism.
8. Current Research
The most widely studied compound derived from this fungus is A. auricula-judae polysaccharides (AAP), which has recently been shown in several studies to possess positive anti-obesity effects in mouse models. One study revealed that mice put on a high fat diet displayed significant reduction in body weight gain and improved lipid metabolism with reduced levels of cholesterol, triglycerides, and LDL cholesterol in the blood when supplemented with AAP versus without supplementation (2). Another study found that AAP modulates the composition of mice gut microbiota, where after analysis of the mice gut microbiome post-AAP supplementation, it was observed that beneficial bacteria such as Lactobacillus and Roseburia associated with improved metabolic health were increased, while harmful bacteria like Proteobacteria that impact intestinal barrier function were reduced (15). This in turn inhibits obesity-linked inflammation pathways (e.g., the TLR4/JNK signaling pathway) and insulin resistance.
In addition to obesity, one study showed AAP’s ability to regulate diabetes-related pathways, such as the AKT/AMPK signaling pathway (15). Mice treated with AAP indicated a significant reduction in blood glucose levels, improved glucose tolerance, and increased insulin sensitivity, making AAP a potential natural remedy to type 2 diabetes.
The first study to evidence the wound-healing effects of AAP has also surfaced in 2021 (17). Through the combination of in-vitro and in-vivo studies in cellular cultures and mouse models, AAP was shown to stimulate fibroblast and keratinocyte cell proliferation, collagen synthesis, and wound closure. These findings showcase AAP’s applications in dermatology and natural medicine for external injuries.
There has also been scientific work that explores eco-friendly sustainable cultivation methods for A. auricula-judae. As the growing demand for A. auricula-judae in Asia requires larger amounts of sawdust and cultivation area, the overexploitation of sawdust and increasing cost to cultivate A. auricula-judae becomes a problem to preserving the ecological environment and achieving sustainable production (4). One group’s research demonstrated that the utilization of waste walnut sawdust as a growth medium enhanced the nutrient and mineral content and growth rate of A. auricula-judae compared to those grown in miscellaneous wood sawdust (4). Researchers believe walnut sawdust to be an optimal growth substrate for environmentally conscious mushroom cultivation.
9. References
[1] [Zhao, Y., Wang, L., Zhang, D., Li, R., Cheng, T., Zhang, Y., Liu, X., Wong, G., Tang, Y., Wang, H., & Gao, S. (2019). Comparative transcriptome analysis reveals relationship of three major domesticated varieties of Auricularia auricula-judae. Scientific reports, 9(1), 78.] [2] [Liu, Q., Ma, R., Li, S., Fei, Y., Lei, J., Li, R., Pan, Y., Liu, S., & Wang, L. (2022). Dietary Supplementation of Auricularia auricula-judae Polysaccharides Alleviate Nutritional Obesity in Mice via Regulating Inflammatory Response and Lipid Metabolism. Foods (Basel, Switzerland), 11(7), 942.] [3] [Yu, Te, et al. “The Current State and Future Prospects of Auricularia Auricula’s Polysaccharide Processing Technology Portfolio.” Molecules (Basel, Switzerland), U.S. National Library of Medicine, 6 Jan. 2023.] [4] [Hao, Z., Zhang, W., Tian, F., Wei, R., & Pan, X. (2022). Enhancing the Nutritional and Functional Properties of Auricularia auricula through the Exploitation of Walnut Branch Waste. Foods, 11(20), 3242.] [5] [Yuan, Y., Wi, F., Si, Jing., Zhao Y., & Dai, Y. Whole genome sequence of Auricularia heimuer (Basidiomycota, Fungi), the third most important cultivated mushroom worldwide, Genomics, Volume 111, Issue 1, 2019, Pages 50-58, ISSN 0888-7543.] [6] [Li Li, et al (2014) “The molecular diversity analysis of Auricularia auricula-judae in China by nuclear ribosomal DNA intergenic spacer”, Electronic Journal of Biotechnology, Volume 17, Issue 1, 2014, Pages 27-33, ISSN 0717-3458.] [7] [Pant, N., Noh, H., Lee, W. H., & Kim, S. H. (2023). Genetic Clarification of Auricularia heimuer Strains Bred and Cultivated in Korea Using the ITS and IGS1 rDNA Region Sequences. Mycobiology, 51(2), 109–113. https://doi.org/10.1080/12298093.2023.2182024] [8] [Zhang, R.Y., Hu, D.D., Gu, J.G. et al. Development of SSR markers for typing cultivars in the mushroom Auricularia auricula-judae . Mycol Progress 11, 587–592 (2012). https://doi.org/10.1007/s11557-011-0798-2] [9] [Wu, F., Tohtirjap, et al (2021). “Global Diversity and Updated Phylogeny of Auricularia (Auriculariales, Basidiomycota)” Journal of fungi (Basel, Switzerland), 7(11), 933. https://doi.org/10.3390/jof7110933] [10] [Zhao, Y., Wang, L., Zhang, D. et al. Comparative transcriptome analysis reveals relationship of three major domesticated varieties of Auricularia auricula-judae. Sci Rep 9, 78 (2019). https://doi.org/10.1038/s41598-018-36984-y] [11] [Jo, W., Kim, D., Seok, S., Jung, H., & Park, S. (2014). The culture conditions for the mycelial growth of Auricularia auricula-judae. Journal of Mushroom. 12. 88-95. 10.14480/JM.2014.12.2.88.] [12] [Encyclopædia Britannica, inc. (n.d.). Saprotroph. Encyclopædia Britannica. https://britannica.com/science/saprotroph] [13] [Tahidul Islam, et al “Insights into Health-Promoting Effects of Jew’s Ear (Auricularia Auricula-Judae).” Trends in Food Science & Technology, Elsevier, 12 June 2021, www.sciencedirect.com/science/article/pii/S0924224421003915. ] [14] [Xu, S., Zhang, Y., & Jiang, K. (2016). Antioxidant activity in vitro and in vivo of the polysaccharides from different varieties of Auricularia Auricula. Food & Function.] [15] [Xu, N., Zhou, Y., Lu, X., & Chang, Y. (2021). Auricularia auricula-judae (Bull.) polysaccharides improve type 2 diabetes in HFD/STZ-induced mice by regulating the AKT/AMPK signaling pathways and the gut microbiota. Journal of food science, 86(12), 5479–5494. https://doi.org/10.1111/1750-3841.15963] [16] [Zhou, Y., Jia, Y., Xu, N., Tang, L., & Chang, Y. (2023). Auricularia auricula-judae (Bull.) polysaccharides improve obesity in mice by regulating gut microbiota and TLR4/JNK signaling pathway. International journal of biological macromolecules, 250, 126172.] [17] [Mapoung, S., Umsumarng, S., Semmarath, W., Arjsri, P., Thippraphan, P., Yodkeeree, S., & Limtrakul (Dejkriengkraikul), P. (2021). Skin wound-healing potential of polysaccharides from medicinal mushroom Auricularia Auricula-Judae (bull.). Journal of Fungi, 7(4), 247.]
Edited by Alex Chen, Jared Chuah, Jie Jie Lin, Zoe Liu, Katherine Zhang, students of Jennifer Bhatnagar for [http://www.bu.edu/academics/cas/courses/cas-bi-311/ BI 311 General Microbiology], 2015, Boston University.
