By Dr. Michelle Seidl, EMLab P&K Analyst
The genus Trichocladium was first described by the German botanist Carl Otto Harz in 1871. A eukaryotic ascomycetous fungus within the family Chaetomiaceae, Index Fungorum lists 35 described species for the genus. Molecular studies support this genus to have affinities with the order Sordariales (Hambleton, et al. 2005). Trichocladium reproduces asexually (mitosporic) and is a dematiaceous (dark pigmented) hyphomycete. Goh & Hyde (1999) provide a literature review of 18 accepted species along with an identification key.
Although rarely abundant, it is detected regularly enough in air samples that it warrants a brief discussion and understanding. In nature, it is saprobic on wood, bark and various other woody and herbaceous plant parts, and has also been isolated from other fungi, soil, and sand. Some species are aquatic or semiaquatic, occurring on submerged plant material, in both freshwater and marine habitats (Shearer & Crane 1977). In the marine environment, 11 species are listed on the World Register of Marine Species (WoRMS). Trichocladium lignicola I. Schmidt has been isolated from submerged beech (Fagus) and pine (Pinus) wood in freshwater systems (Kane, et al. 2002).
Reports of Trichocladium on various plants in North America include: Douglas fir (Pseudotsuga), hemlock (Tsuga), pea (Pisum), vetch (Vicia), hogweed (Heracleum), nettle (Urtica), chestnut (Castanea), beech (Fagus), oak (Quercus), ash (Fraxinus), poplar (Populus) and maple (Acer) (Ellis & Ellis 1997; http://pnwfungi.wsu.edu/). Trichocladium canadense S. Hughes is frequently one of the fungi isolated from discolored wood associated with wounds of sugar maple (Acer saccharum Marsh.) and some species of birch (Betula), beech (Fagus) and ash (Fraxinus). The discolored wood is also found to be high in manganese, calcium, zinc and iron, as well as correlated with an increase in growth (Shigo 1974).
Identified as an outside indicator spore, very little information is available regarding human health effects. In spore trap samples, Trichocladium is recovered most frequently in the late summer to early fall (August, September, October) and the lowest recovery rates are in winter (December, January, February) (Figure 1). The state with the highest number of samples recorded geographically is Florida (9% of total records), while the lowest is Wyoming (0.09%).
Figure 1: Frequency of detection for Trichocladium.
Source: EMLab P&K MoldRANGE data. Total sample size for this graph: 265,118.
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Certain species can be identified in air by culturable samples (e.g., Andersen samples). This organism generally does not grow well on general fungal laboratory media. Colonies form brown to dark brown, or grey to black, loosely spreading colonies (Ellis 1971). Trichocladium can be identified from all nonviable analyses. Primarily seen in spore trap samples, we also detect this genus from tape lifts, swabs, and bulk samples. It is often detected from woody substrates.
The spores (conidia) of some species have a distinctive morphology (Figure 2), while others are not so distinctive, and therefore identified simply as brown spore type. There is some confusion in identifying this genus, but the main conidial features are solitary and borne directly and laterally on hyphae. Conidia are thick-walled, 1-many septate, brown colored (particularly the basal cell), more or less pyriform (pear-shaped) to clavate (club-shaped), elliptical, subglobose or obclavate in shape. The spore surface can be smooth, roughened, occasionally lobed, and with or without a germ pore. Trichocladium is heterogeneous and species identification is nothing less than difficult.
Figure 2: Microscopic photo of Trichocladium conidia showing prominent pore and septation.
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Allergenicity has not been studied for Trichocladium. There have been 2 reported cases of keratitis (inflammation of the eye's cornea) (Petch 1922; Batista & Upadhyay 1965). A few newly described, cytotoxic metabolites known as Trichocladinols, were recently described and isolated from cultures of Trichocladium colonizing the ascomycete fungus Cordyceps (Guo, et al. 2009). These novel compounds have shown modest cytotoxic effects against two human tumor cell lines.
And finally, from a survey examining microbes in ancient tombs, Trichocladium asperum Harz was among the isolates (Sprocati, et al. 2008), and thought to possibly contribute to the overall deterioration.
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2. Ellis, M. B. 1971. Dematiaceous Hyphomycetes. CMI, Kew, England. 608 pp.
3. Ellis, M. B. & J. P. Ellis. 1997. Microfungi on land plants: an identification handbook. 2nd edition. Richmond Publishing Co. Ltd. UK.
4. Chatmala, I., J. Sakayaroj, S. Somrithipol & S. Phongpaichit. 2004. Marine Hyphomycetes of Thailand and Cumulospora varia sp. nov. Fungal Diversity 17: 1-9.
5. Goh, T. K. & K. D. Hyde. 1999. A synopsis of Trichocladium species, based on the literature. Fungal Diversity 2:101-118.
6. Guo, H., B. Sun, H. Gao, S. Niu, X. Liu, X. Yao & Y. Che. 2009. Trichocladinols A-C, cytotoxic metabolites from a Cordyceps colonizing ascomycete Trichocladium opaceum. European J. Organic Chem. 32: 5525-5530.
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8. Kane, D. F., W. Y. Tam & E. B. G. Jones. 2002. Fungi colonising and sporulating on submerged wood in the River Severn, UK. In: Fungal Succession (eds. K.D. Hyde & E.B.G. Jones). Fungal Diversity 10:45-55.
9. Petch, T. 1922. Additions to Ceylon fungi. II. Annals of the Royal Botanic Gardens, Peradeniya 7:318.
10. Shearer, C. A. & J. L. Crane. 1977. Fungi of the Chesapeake Bay and its tributaries VI. Trichocladium achrasporum, the imperfect state of Halosphaeria mediosetigera, a marine ascomycete. Mycologia 69(6):1218-1223.
11. Shigo, Alex L. 1974. Effects of manganese, calcium, zinc and iron on growth and pigmentation of Trichocladium canadense, Phialophora melinii, Hypoxylon rubiginosum, Daldinia concentrica, and Cytospora decipiens. Mycologia 66(2):339-341.
12. Sprocati, A. R., C. Alisi, F. Tasso, E. Vedovato, N. Barbabietola & C. Cremisini. 2008. A microbiological survey of the Etruscan mercareccia tomb (Italy): contribution of microorganisms to deterioration and restoration. 9th Int. Conf. on Art, Jerusalem, Israel. 25-30 May.
This article was originally published on October 2010.