Abstrakt
Fungi are a diverse group of microorganisms ubiquitously present in natural ecosystems and they are regarded as the major decomposers of complex biomaterials. Fungi can thrive in a huge variety of habitats, ranging from surface waters to terrestrial environments-including extreme zones of the biosphere like deserts or polar regions-and they use air to disperse their propagules.
Regardless of their taxonomic classification, all fungi are essentially heterotrophic microorganisms. In general terms, they can be subdivided into biotrophic and saprotrophic organisms based on their ecophysiology.
The first group encompasses symbionts and pathogens of other species, while the second is the group of "decomposers" of biomass. Although several studies have highlighted the ecological importance of some biotrophic fungi, for the rationale of this chapter, which deals with the importance of fungi in the decontamination of polluted environments, saprotrophic fungi are more significant.
Saprophytic fungi are able to decompose and transform a wide array of organic substrates. In contrast to bacteria, which need to transport nutrients into their intracellular compartment prior to their utilization, fungal mycelia can be seen as "externalized stomachs" which secrete their hydrolytic enzymes and organic acids into the extracellular environment and transport digested substances and chelates inside their cell wall.
Although bacteria are, to some extent, faster and more efficient than fungi in utilizing readily assimilable substrates (proteins, lipids, starch and free sugars), fungi have evolved extremely efficient enzymatic machineries for the degradation of complex nonprotein polymers, such as lignocellulose and chitin, which are inaccessible and/or recalcitrant to the majority of prokaryotes. Due to these unique capabilities, fungi are considered to play key roles in a number of biogeochemical processes and, more generally, in the cycling of carbon and other elements.