Saturday 14 August 2010

Chaetomium Species

Chaetomium Species

Had some fun playing with this fungus in getting the ascoma (perithicium) to develop for these photographs. Still trying a few tricks so additional photos may be posted later.

In the clinical laboratory, media available is geared towards economical, rapid and efficient identification of the most common human pathogens. Unfortunately, resources (specialized media) are scarce if one wishes to experiment with ‘environmental’ organisms. Although generally considered to a saprophyte, these days virtually any organism can be responsible for disease in the imunocompromised host. Chaetomium has been implicated as agents of onychomycosis, peritonitis as well as having caused cutaneous lesions.

There are over 180 known species of Chaetomium, many of which are active in the breakdown of cellulose in the environment. Items such as paper or textiles in contact with soil, straw, dung etc decompose in part, due to the action of Chaetomium.

I believe the species I have here is Chaetomium globosum, one of the most common and widely distributed species of Chaetomium.

Pale yellow to a greyish-green depending on media and length of growth. Relatively rapid growth. Does not grow at 42 Celcius.

Hyaline septate hyphae. Ascoma (Perithecia) are spherical to ovoidal to obovoidal (175 - 200 µm in length) with numerous hairs, usually unbranched, flexsulose, undulating or coiled, septate, brownish in colour and up to 500 µm in length.
Asci are clavate (30 - 40 X 11 - 16 µm in size) containing eight brownish limoniform (in face view) ascospores 9 - 10 X 8 - 10 µm in size.

Photographs below were taken using sticky-tape preparations, slide cultures on SAB media as well as growing the fungus on somewhat nutritionally deficient Corn Meal Agar, partially covered with a cover slip to vary the atmospheric tension. Ascoma were best seen on the slide culture and at the edges of the cover slip after about 14 days of incubation.

Still haven’t managed to induce and photograph the asci and ascospores. From what I understand, the fruiting of Chaetomium in culture can be stimulated by the addition of cellulose in the form of filter paper, cloth or jute fiber. It seems that compounds excreted by the fungus Aspergillus fumigatus can stimulate fruiting as well. Sugar phosphates and phospho-glyceric acid, by-products produced by A. fumigatus have been shown to stimulate the production of asci and ascospores. Calcium may also have an effect on fruiting. Perhaps I’ll play around with a few of these to see if I can induce fruiting structures for future photographs.

Plate at right is Chaetomium on SAB after about 96 hours incubation at 30 C.

Chaetomium in slide culture growing on edge of corn meal agar as seen after about 14 days incubation at 30C (X100)

Chaetomium ascoma on Corn Meal Agar at about 10 -14 Days (x100)

Chaetomium ascoma

I just think they look cute! Only a microbiologist would understand...

Lacto Phenol Cotton Blue (LPCB) Tape Preparation

Chaetomium ascoma and ascospores ejected at top

Slide Culture (SAB) ~12 Days -x100

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