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Figure 10.4 Diagram of five diurnally fluctuating temperature regimes used to study competitive growth of a mixed soil fungal flora in soil plates in nutrient medium. (From Rajasekaran and Maheshwari (1993).)

In yet another approach, Rajasekaran and Maheshwari (1993) used immunofluorescence microscopy to detect the growth of a ubiquitous thermophilic fungus in soil. Spores of Thermomyces lanuginosus were adhered to glass cover slips and buried in field soil where moisture levels seemed favorable for microbial growth. The soil temperature varied between 22 and 28°C during the time of the experiment. After three weeks, the cover slips supporting the spores were retrieved and stained with fluorescein isothiocyanate (FITC) conjugated antibody prepared using germinating spores of the test fungus. Only dormant spores were seen, although spores similarly placed in petri dishes in unsterilized soil at 50°C in a laboratory incubator had germinated. These results did not support the view that soil is a "natural habitat" of thermophilic fungi.

Various air-sampling devices have captured spores of thermophilic fungi from air even in the temperate regions. The aerial dissemination of spores from world-wide composts of various types and their fall-out from air can explain the widespread occurrence of thermophilic propagules in soil. The concentration of spores of thermophilic fungi per gram material is approximately 106 times higher in composts than in soils (see Maheshwari, 1997). Thermophilic fungi are primarily compost fungi.

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