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Chaetomium aureum is a saprophytic and endophytic fungus that can derive nutrients from non-living plant tissue and from living plant hosts. It can degrade cellulose and often produces colored exudates in culture. It is an ascomycete teleomorph. Like all Chaetomium species, its perithecia are covered in hairs; C. aureum displays relatively straight hairs when compared to other members of Chaetomium, curving back on themselves or curling at the tips.

Ecology
Chaetomium aureum is a cellulolytic organism, meaning it can produce enzymes, called cellulases, that degrade cellulose. Cellulose is the major component of all plant cell walls, and these cellulases allow C. aureum to break down plant tissue to use as a source of carbon. It can break down cellulose in many configurations including wood and cloth, which allows it to colonize areas that other fungi cannot, including paper and cotton fabrics. Chaetomium aureum displays several different life strategies, including being a saprobe and an endophyte, and is not typically found as a parasite or pathogen causing any known disease. As a saprobe, C. aureum absorbs nutrients from dead and decaying materials. Guinea pig dung from Massachusetts, U.S.; hemlock bark (Tsuga sp.) from Michigan, U.S.; soil from the Czech Republic, United States, Ecuador, and South Africa; and compost in Brazil are documented examples of substrates C. aureum is capable of utilizing.

As an endophyte, C. aureum lives and grows inside the tissues of a plant host, feeding on nutrients produced or collected by the plant. Endophytes that do not cause any signs of disease can become pathogenic under certain conditions, but C. aureum has not been shown to cause disease. Chaetomium aureum has been shown to colonize several cultivars of strawberry (Fragaria sp.) in Canada, found in crown tissue and more often in root tissue. These strawberry plants infected with C. aureum did not show signs of disease, but C. cochliodes was implicated in strawberry crown and root rots. Chaetomium aureum has been recovered from inside seeds of many plants, including tomato (Solanum lycopersicum) from Ontario, Canada; cucumber (Cucumis sativa) from Michigan, U.S.; pepper (Capsicum annuum) from New Jersey, U.S.; carrot (Daucus carota var. sativa) and oats (Avena sativa) from Quebec, Canada; and onion (Allium cepa) from British Columbia, Canada. Chaetomium aureum also has known associations with oil palm (Elaeis guineensis) seedling roots from the Malay Peninsula; Virginia pine (Pinus virginiana) from Indiana, U.S.; and Scots pine (Pinus sylvestris) and English oak (Quercus robur) from Norway. Not much research has been done on monocot, particularly cereal grain, associations with Chaetomium species. Future research may yield a similarly broad host range as seen in vegetable seeds and gymnosperms.

Clearly, this species has a global distribution spanning many continents including North and South America, Europe, Asia, and Africa. It can grow on many different substrates in nature, and on both dead and living plant tissue; it can be considered a generalist. In artificial culture, C. aureum readily utilizes sodium nitrate as a sole nitrogen source at 25, 30, and 35 °C. It will not grow at 42 °C. In vitro experiments on PDA suggest optimum temperature and initial media pH for C. aureum spore production is about 25 °C and 8, respectively; and 35 °C and 11 for colony diameter (see graphs below based on Wang et al.).

Morphology
Chaetomium species share a common colony morphology in culture. Their septate mycelia radiate from the point of inoculation in conglomerate masses that resemble rope. Chaetomium aureum colonies specifically can often be colored by red, yellow, or green exudates. This coloration helps to distinguish among species in the genus.

Sexual reproduction can occur in the same strain of this species, meaning only one organism is required, because it is homothallic. The ascospores (sexual spores) are single-celled, inequilaterally fusiform or navicular (comma shaped), and have either one germ pore or two, one at each apex. The ascospores are produced in a clavate (club-shaped) ascus, having a short stalk and bearing eight ascospores; the asci break down and can no longer be found after spore release (these asci are considered evanescent). This species appears to lack croziers. Asci form inside a protective structure called a perithecium. The name "aureum" is a reflection of this species' mature perithecia having a golden color. The perithecia of C. aureum are spherical to ovate with an ostiole, superficial (grow on the surface of the medium), and have numerous hair-like projections growing on the outer surface. The hairs in this species are septate and olive-yellow, being fairly straight, with curled tips. The hairs may help protect the perithecia from predation by insect larvae. Mature ascospores are oozed through the ostiole in a column of mucus called a cirrhus. This cirrhus can become so long that it will recurve and reach the surface of the media, pushing against it and 'uprooting' the perithecium. Chaetomium spores are not forcibly ejected (are not ballistospores) and must rely on other means of dispersal. Mucus and spore suspension of the cirrhus can be caught on the perithecial hairs. Once dry, the spores can be suspended in air currents and blown to new substrates. The mucoid mass of spores is characteristic of spores that are dispersed via arthropod contact presumably because spores would attach to arthropods as they pass the perithecium. Particularly on dung substrates, arthropods are attracted to the substrate and brush against the hairs while crawling over the dung. The arthropod leaves the dung with spores attached. Spores are then deposited on new substrates when they fall off the arthropod. Arthropod dispersal seems predominant for fungal species in the dung substrates that attract them, while air dispersal would be the primary mode of dispersal in soil or superficially growing colonies on plant tissue. Another possible dispersal mechanism is persisting on dead plant matter, such as C. aureum growing on bark of wood transported to new locations by humans wanting to use the wood. Few dispersal studies exist for Chaetomium species.

Asexual reproduction is unknown because no anamorph has been identified for this species. Anamorphs for some other Chaetomium species have been reported. Botryotrichum piluliferum and Paecilomyces species are both reported anamorphs of Chaetomium piluliferum. Acremonium species are the reported anamorph of C. elatum. A Trichocladium species was also proposed in general for Chaetomium species. There is not much information on Chaetomium anamorphs in the literature, and Chaetomium ascospores typically germinate to produce more perithecia, lacking conidiophores and conidia. Focused study on the reported anamorph-teleomorph relationships known in Chaetomium could shed light on the conditions under which the seemingly dominant teleomorphs display anamorphic fruiting structures.

Systematics
Chivers first described C. aureum in 1912, isolated from paper and dung, noting its “small size, ... characteristic golden yellow color, ... long black cirrhi, ... comparative obscurity of the perithecial hairs at maturity, ... incurved tips of the terminal hairs, ... and irregular, oval shape of its spores” as characters that distinguished C. aureum from other Chaetomium species.

Morphological characters have historically been used to classify this species, particularly perethecial hair shape and the possible presence of two germ pores on each ascospore. A molecular phylogenetic study published in 1999 comparing small subunit (SSU) ribosomal DNA (rDNA) of different fungal species and genera considered related to Chaetomium suggests that Chaetomium aureum is closely related to Chaetomium elatum. A 2011 study on Chaetomium species in Iran based on large subunit (LSU) and internal transcribed spacer (ITS) rDNA and β-tubulin found sister relationship between C. elatum and C. rectangulare; and this clade was found to be sister to a clade containing C. coarctatum, C. subaffine, and C. undulatulum. This suggests that these Chaetomium species are also closely related to C. aureum, though further study including C. aureum samples is needed to test this hypothesis. While phylogenetic information exists for Chaetomium species in general, less work has been done that includes C. aureum, and a more inclusive phylogenetic study would increase the understanding of how C. aureum fits into the evolutionary history of the genus.

Taxonomic relatedness based on morphological features between C. aureum and other Chaetomium biporate ascospore species such as C. virescens to other biporate ascospore genera such as Melanospora, Lophotrichus, and Neurospora was suggested by von Arx in 1984. The 1999 SSU rDNA study supported a close affinity to Neurospora crassa - N. crassa resides in a sister clade to the Chaetomium clade; Lophotrichus species were more distantly related, and Melanospora was not included in the phylogeny. Another phylogenetic study, this one using concatenated SSU and large subunit (LSU) ribosomal RNA, translation elongation factor (TEF), and RNA polymerase II second largest subunit (RPB2) genes, supports the sister relationship between Chaetomium and a clade containing Neurospora crassa; Melanospora was also not studied. Inclusion of more Chaetomium species in broad phylogenetic studies would elucidate genera and species relationships for this group, as current research typically includes many Chaetomium species and few other genera, or many other genera and few Chaetomium species.

Separate Chaetomium species have been described and later classified as actually being C. aureum, three of which were described in 1966 by Warmelo. These three species are C. confusum, C. humicolum, and C. rubrogenum. C. confusum produces dark brown-green mycelia without coloring the agar; C. humicolum produces dark green mycelia with colored water soluble exudates; and C. rubrogenum produces gray mycelia which colored the agar a bright red with exudates. Each species can produce long cirrhi occasionally, if not often. All perithecial hairs are slightly curved, with slightly curled ends. The shared colored mycelia and exudates, cirrhi, and perithecial hairs may be why these three species are now classified as C. aureum, though specific reasons are not clearly stated in the synonymy databases. C. confusum and C. humicolum are also reported to have biporate ascospores. The three Warmelo species were originally classified as new species because of smaller perithecia, and dark ascospores, among other characters, though the 'new' species descriptions seem to fit C. aureum characters.

Two subspecies of C. trilaterale - C. trilaterale var. diporum and C. trilaterale var. trilaterale - were also recorded as synonyms of C. aureum, also without explanation. These two varieties are both described as having two germ pores on their ascospores, a characteristic distinct from the other C. trilaterale varieties, explaining their classification as separate varieties. These isolates were reported to form croziers, which does not agree with previous research on C. aureum. This biporate characteristic could be why C. trilaterale var. trilaterale and var. diporum are listed as C. aureum synonyms, though crozier formation is not indicated for C. aureum. Phylogenetic and breeding studies could be used to resolve these species and varieties into C. aureum or as separate, distinct species as described.

Potential as a Biological Control Agent
Some information exists at present regarding Chaetomium species being used as biological control agents to manage certain plant pathogenic organisms. Several Chaetomium species were tested for activity against Pythium aphanidermatum, which causes damping off and root rot of many different crop plants. The Chaetomium isolates were grown in culture and their mycelia was ground up: contents were extracted via dissolving in a series of solvents. Chaetomium aureum mycelial extract was shown to reduce P. aphanidermatum oospore formation in vitro, though not as strongly as Chaetomium cochliodes. It is believed that this inhibition is achieved by "lysis and antibiosis". Mycelial extract thus represents a potential biological control derived from Chaetomium species to combat P. aphanidermatum. In vivo studies on the topic are necessary to assess the extent and feasibility of control achievable by this method.

Wang, et. al (2013) isolated C. aureum from rhizosphere soil in China and tested it for managing the rice diseases rice blast caused by Magnaporthe grisea and sheath blight caused by Rhizoctonia solani. Exudates from C. aureum were harvested from colonies. These exudates reduced conidia germination and appresorium formation of M. grisea and inhibited mycelia growth of R. solani during the in vitro experiment. When sprayed onto rice plants in vivo, the exudate solution reduced disease severity of both rice blast and sheath blight. Colony exudates from C. aureum could potentially be used to help control rice blast and sheath blight when applied as a foliar spray. More research concerning effects of the foliar spray on rice yield would help determine if the C. aureum colony exudate could be economically produced and applied in this manner, and if other Chaetomium species might have a similar effect.