ABSTRACT
The adaptation of thermophiles to high temperatures is a combination of different strategies, including genetic selection and functional acclimatization. Cellular components such as lipids, nucleic acids, and proteins are usually thermolabile. Genomics studies of thermophiles have revealed that the evolution of thermal tolerance depends on the levels of heritable variations, for example, reduction in genome size, horizontal DNA transfer, and gene mutation. While thermophilism refers to the stability of the entire functioning organism based on its genetic constitution, thermal stability encompasses the stability of an individual cellular component or process independent of other components or processes. This chapter begins with an introduction to the origin and ecological relationships of thermophilic fungi, and how these fungi have adapted to elevated temperatures in environments in which most of their close relatives fail to survive. Further, various hypotheses to explain thermophilism in fungi, including protein thermostability and stabilization, heat shock proteins, proteomes and genomes as determinants of thermophilic adaptation, reduction in genome size, thermotolerance genes, rapid turnover of essential metabolites, macromolecular thermostability, ultrastructural thermostability, and pigmentation and lipid solubilization, have been discussed with reference to various available theories. Finally, acquired thermotolerance in fungi and homeoviscous versus homeophasic adaptation of molecules in thermophilic fungi are presented.
