Ten years of sharpening a sword - the Institute of Microbiology, Chinese Academy of Sciences established a modern classification system for Chaetaceae fungi

Fungi of the family Chaetomiaceae are a resource library of cellulases and biologically active metabolites with great application potential
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Most of the thermophilic species in the fungi kingdom belong to Chaeteaceae.
The enzymes produced by these species show the highest enzymatic activity at high temperature of 50℃～70℃
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So far, there are more than 400 kinds of secondary metabolites with different structures produced by species within the family, most of which have biological activities such as anti-tumor, anti-malarial, anti-fungal, anti-bacterial, cytotoxic, and enzyme inhibitor
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A few species have been found to produce carcinogenic aflatoxin precursors, sterigmatocystin
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Chaetaeaceae is also a common indoor pollution fungus, which can cause health problems such as allergies.
A few species can directly infect the surface tissues of immune-sound people, and some species can invade the brain center, lungs and other deep tissues of immunocompromised patients, causing fatal infections.

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Chaetomidae is a high-value group in the fungal kingdom.
They produce beautiful ascomas of various shapes through sexual reproduction, thus attracting many researchers
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Since the first species, Chaetomium globosum, was discovered in 1817, more than 400 species have been described successively, and at least 8 monographs on morphological classification have been published, but without exception, they only focus on sexual reproduction species
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Molecular evidence suggests that at least seven vegetative genera are members of the Chaeteaceae family, but their location within the family and their relationship to sexually-reproducing species are unknown
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Dr.
Wang Xuewei from Bai Fengyan's research group in the State Key Laboratory of Mycology, when studying the diversity of Chaeteaceae fungi in China, realized that there is obvious subjective artificiality in the morphological classification system.
All are classified into the type genus - Chaetomium, while the species of ascomas without pores and hairs, or underdeveloped hairs are classified into the genus Thielavia, which are the two largest genera in the family
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In 2013, Dr.
Xuewei Wang was invited by Prof.
Pedro Crous, director of the Westerdijk Institute of Fungal Diversity (formerly CBS) of the Royal Netherlands Academy of Sciences, to start research on Chaetomidae fungi in the world
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Through analysis and comparison, the research group first determined the best molecular markers to distinguish different genera and species within the family, and established a set of methods to observe and study different morphological structures such as ascomas, ascus, ascospores, and asexual reproduction structures (as shown in Figure 1, 2)
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On this basis, using comprehensive research methods such as multi-gene (ITS, LSU, rpb2, β-tubulin) phylogenetic analysis + morphological observation + ecological adaptation comparison, more than 1,000 strains preserved in CBS from different countries and regions around the world were analyzed.
The sexual and asexual reproduction strains in the region have been systematically studied for nearly 9 years
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The results of the study have completely overturned the morphological classification system that has been in use for nearly 200 years, and established a modern classification system of Chaetomidae, which is composed of 50 monophyletic genera, tends to be natural, and can reflect the evolutionary relationship between different genera and species.
The results and important revisions made are as follows: (1) The study proves that Chaetomidae is a monophyletic group, but most of the genera in the original family are polyphyletic, including model genera
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The research team subsequently redefined or revised 15 known genera within the family (Fig.
3)
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Taking Chaetomium and Thielavia as examples, the study proved that the species originally put into Chaetomium according to their morphology were scattered in Chaetomium sensu stricto and 22 other genera unrelated to each other (Fig.
3); the original type species of Thielavia, Th.
Melanosporales (Melanosporales, the base of Fig.
3) is a distantly related fungal parasitic species, while other species in the original genus are saprophytic, and are scattered in 11 genera of the family Chaeteaceae and the family Chaeteaceae.
A genus within the sister group Podosporaceae (Fig.
3)
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Corrected the misplacement of multiple genera/species of orders and families in the traditional classification system
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(2) A new family, Podosporaceae (Fig.
3), was established; 23 new genera (Fig.
3), 45 new species and 101 new assemblages were established
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(3) The phylogenetic relationship between vegetative and sexually propagated species within the family was clarified (Fig.
3)
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(4) Molecular clock analysis based on 5.
8 S ribosomal DNA, LSU, rpb2, and β-tubulin, verified the monophyletic genera within the family, which differentiated and formed at least 27 million years ago
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(5) The phylogenetic position of thermophilic species in Chaetomidae was clarified
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The optimum growth temperature of these species is about 45°C, and they belong to 7 different genera
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Molecular clock analysis revealed that they separated from non-thermophilic species at least 30 million years ago, forming 7 lineages independent of each other, of which only Mycothermus and Remersonia formed a sister group, proving that thermophilic species within Chaetomidae at least Independence originated 6 times
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(6) By studying 145 Chaetomidae strains from indoor environments of 19 countries on five continents, the species diversity of Chaetomidae fungi in the global indoor environment was clarified: 33 species were included, of which the most common indoor pollutant species was Chaetomium globosum
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In addition, nearly 200 species in the family have been re-described, with high-quality morphological characteristic color plates reflecting the complete morphological characteristics of each species, to help those who need it to quickly identify these species in the Chaetomidae according to their morphology
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Since von Arx et al.
published the last monograph on the morphological classification of Chaetomidae in 1986, the taxonomic research of this family has almost stagnated.
In the past 30 years, only 4 new genera and more than ten new species have been published
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The research work of Bai Fengyan's group has activated the modern taxonomic research of Chaetomidae, and other foreign researchers have established 6 new genera between 2018 and 2021 alone
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Wang Xuewei's morphological work is especially appreciated by her peers
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Professor Pedro Crous, Director of the Westerdijk Institute, sent an email the day after the latest results of the research group were published online, saying "Dear Xuewei, I am sitting here looking at your paper, and I wonder how you could get these fungi to appear so beautifully as they do.
It's truly more art than anything else! Congratulations.
This is next level – very nice indeed!" The above work has been published in the top journals in the field of mycology, Studies in Mycology (4 articles) and Persoonia (1 article).
Funded by the Alfred Sloan Foundation Programme on the Microbiology of the Built Environment (Grant No.
G-2014-14529), the National Natural Science Foundation of China and China Agricultural University
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 Related articles and links: Wang XW, PJ Han, FY Bai, A.
Luo, K.
Bensch, M.
Meijer, B.
Kraak, DY Han, BD Sun, PW Crous, J.
Houbraken.
Taxonomy, phylogeny and identification of Chaetomiaceae with emphasis on thermophilic species.
Studies in Mycology 2022, 101: 121–243.
https:// Wang XW, Yang FY, Meijer M, Kraak B, Sun BD, Jiang YL , Wu YM, Bai FY, Seifert KA, Crous PW, Samson RA, Houbraken J.
Redefining Humicola sensu stricto and related genera in the Chaetomiaceae.
Studies in Mycology 2019, 93: 65–153.
https://doi.
org/10.
1016 /j.
simyco.
2018.
07.
001Wang XW, Bai FY, Bensch K, Meijer M, Sun BD, Han YF, Crous PW, Samson RA, Yang FY, Houbraken J.
Phylogenetic re-evaluation of Thielavia with the introduction of a new family Podosporaceae.
Studies in Mycology 2019, 93: 155–252.
https://doi.
org/10.
1016/j.
simyco.
2019.
08.
002 Wang XW, J.
Houbraken, JZ Groenewald, M.
Meijier, B.
Andersen, KF Nielsen, PW Crous, RA Samson , Diversity and taxonomy of Chaetomium and chaetomium-like fungi from indoor environments.
Studies in Mycology 2016, 84: 145–224.
https://doi.
org/10.
1016/j.
simyco.
2016.
11.
005 Wang XW, Lombard L, Groenewald JZ, Li J, Videira S, Samson RA, Liu XZ, Crous PW, Phylogenetic reassessment of the Chaetomium globosum species complex.
Persoonia 2016, 36: 83–133.
https://doi.
org/10.
3767/003158516X689657Samson RA, Liu XZ, Crous PW, Phylogenetic reassessment of the Chaetomium globosum species complex.
Persoonia 2016, 36: 83–133.
https://doi.
org/10.
3767/003158516X689657Samson RA, Liu XZ, Crous PW, Phylogenetic reassessment of the Chaetomium globosum species complex.
Persoonia 2016, 36: 83–133.
https://doi.
org/10.
3767/003158516X689657