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This study has divided the most frequently isolated types of moderate thermophiles into three groups: isolates of Sulfobacillus thermosulfidooxidans (mol% G C 47-50), an isolate referred to as strain NAL and other closely related species (mol% G C 54-57), and the type previously referred to as strain TH3 (mol% G C 68).An enrichment culture was obtained that could efficiently solubilise a range of mineral sulphides at 48o C under air.Fungal secretomes of all 105 strains produced during growth on untreated rice straw were studied for lignocellulolytic activity at different p H and temperatures.
There is no consensus on the demarcation between the two groups, but typically, a fungus that has a thermal maximum near 50 °C and a minimum below 20 °C is regarded as thermotolerant, while those that grow at 50 °C or above, but not grow at 20 °C or above are regarded as thermophilic.
In the present study, the cultivation temperature was maintained at 50 °C during initial screening for thermophilic fungi.
Among the estimated 3.0 million fungal species existing in nature, and approximately 100 000 species described, only about 50 species have been found to be able to grow at 50–60 °C.
Fungi capable of growing at elevated temperatures are classified into thermophilic and thermotolerant groups.
Most thermophilic fungi also grow well at moderate temperatures and can be found in various substrates, including soils, composts, piles of hay, stored grains, wood chip piles, nesting materials of birds and animals or in municipal refuse.
While thermotolerant/thermophilic fungi appear to be exceedingly rare, fungi able to tolerate acidic conditions are frequently encountered in nature, and many species have been shown to be capable of growing at p H levels as low as 2.Hereafter, we refer to acidophilic species as those optimally growing at p H values below 3, while acidotolerant species refer to species able to grow in acidic environments but with growth optima above p H 3.The earliest description of acidophilic fungi dates back to 1943, when a strain of Acontium velatum and a “Fungus D” were shown to be capable of growing in glucose medium containing 1.25 M sulphuric acid at p H 0.Unfortunately, the strain of Acontium velatum appears to have been lost since the initial publication, but “Fungus D” is now believed to be a strain of Acidomyces acidophilus which is commonly found in extremely acidic environments.Until now, acidophility has been shown for only 6 fungal species, including Acidomyces acidophilus (MB#511856) (=Scytalidium acidophilum = Acidomyces richmondensis = Fungus D), Acidomyces acidothermus (MB#564520), Acidothrix acidophila (MB#805424), Acidea extrema (MB#805425), Acontium velatum (MB#142596, no living specimen available) and Hortaea acidophila (MB#367373) (=Neohortaea acidophila). MEY-1, well-known for the production of a range of thermophilic and acid-tolerant lignocellulolytic enzymes.strains exhibited both higher thermal stability and tolerance to acidic conditions.The study highlights the vast potential of an untapped diversity of thermophilic fungi in the tropics., and only a small number of fungal species thrive at such high temperatures.A range of genes encoding lignocellulolytic enzymes in the acidophilic fungus Acidomyces acidothermus MEY-1 has been cloned and expressed.The enzymes were found to be thermotolerant and functional under acidic conditions.Thermophilic fungi can represent a rich source of industrially relevant enzymes.Here, 105 fungal strains capable of growing at 50 °C and p H 2.0 were isolated from compost and decaying plant matter.