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Microcolonial fungi (MCF) are the most stress-resistant eukaryotes known to date. Black fungi are an interesting object to study mechanisms of stress resistance and to perform applied research to prevent material colonization and biodeterioration. Pigments, like melanin and carotenoids, have been proven to contribute to the unique robustness of MFCs. We study how these pigments ameliorate oxidative stress responses - one of the most significant environmental challenges encountered by MCF - using the model rock fungus Knufia petricola (Chaetothyriales) strain A95.
The roles extracellular polymeric substances (EPS) play in mineral attachment and weathering were studied using genetically modified biofilms of the rock-inhabiting fungus Knufia petricola strain A95. Mutants deficient in melanin and/or carotenoid synthesis were grown as air-exposed biofilms. Extracted EPS were quantified and characterised using a combination of analytical techniques. The absence of melanin affected the quantity and composition of the produced EPS: mutants no longer able to form melanin synthesised more EPS containing fewer pullulan-related glycosidic linkages. Moreover, the melanin-producing strains attached more strongly to the mineral olivine and dissolved it at a higher rate. We hypothesise that the pullulan-related linkages, with their known adhesion functionality, enable fungal attachment and weathering. The released phenolic intermediates of melanin synthesis in the Δsdh1 mutant might play a role similar to Fe-chelating siderophores, driving olivine dissolution even further. These data demonstrate the need for careful compositional and quantitative analyses of biofilm-created microenvironments.
Territories of rock-inhabiting fungi: Survival on and alteration of solid air-exposed surfaces
(2018)
Subaerial biofilms that are omnipresent at the interface between all solid substrates and the atmosphere are composed of a unique and widespread group of ascomycetes called rock-inhabiting fungi or microcolonial fungi (MCF), typically in communities with other microorganisms. While subaerial biofilms in toto have important roles in mineral weathering and biodeterioration of materials, methodological approaches to subaerial biofilm communities are diverse and frequently focussed on MCF. Here, we review the historical development of the research methods applied in the field and consider perspectives to increase our understanding of the biofilm-induced changes of solid substrate surfaces.
Targeted disruption of melanin synthesis in rock-inhabiting fungi - a new tool in material science
(2016)
Melanised rock-inhabiting fungi are found in extreme habitats and along broad spectrum of economically important man-made materials. Black fungi and accompanying organisms can weather rocks and cause significant losses in light availability to solar parks. Understanding these underlying mechanisms requires a set of modern biological techniques and approaches that are under development in our laboratory.
Black ascomycetous microcolonial fungi (MCF) are persistent inhabitants of rock surfaces in deserts as well as ubiquitous in other wide-spread terrestrial ecosystems including man-made materials such as solar panels. The ability of MCF to cope with multiple, rapidly fluctuating stresses makes the group an interesting subject in the study of stress resistance. Carotenoids and melanin are amongst the protective pigments that contribute to the robustness of MCF. We studied their role in stress resistance of the non-pathogenic rock-inhabiting fungus Knufia petricola (Chaetothyriales) strain A95. Disruption of melanin synthesis affects not only oxidative-stress resistance but also the extracellular polysaccharide (EPS) matrix and lipid composition of the cell membrane.
Black ascomycetous microcolonial fungi (MCF) are persistent inhabitants of rock surfaces in deserts as well as ubiquitous in other wide-spread terrestrial ecosystems including man-made materials such as solar panels. The ability of MCF to cope with multiple, rapidly fluctuating stresses makes the group an interesting subject in the study of stress resistance. Carotenoids and melanin are amongst the protective pigments that contribute to the robustness of MCF. We studied their role in stress resistance of the non-pathogenic rock-inhabiting fungus Knufia petricola (Chaetothyriales) strain A95. Disruption of melanin synthesis affects not only oxidative-stress resistance but also the extracellular polysaccharide (EPS) matrix and lipid composition of the cell membrane.
Fungal extracellular materials reinforce a constant interaction between their cell wall and the environment. A dynamic mixture of chitin, glucans, mannans, glycoproteins, glycolipids and pigments supports the success of all fungal life styles – from symbiotic to the free-living and pathogenic. Fungi are perfectly adapted to grow on surfaces and in porous environments, where they form medically and geochemically relevant biofilms. Fungal EPS are critical in adhesion to other fungi, other cells or substratum as well as in the following interaction with the host immune system or material they attack, degrade and deteriorate respectively. Characterisation of extracellular compounds and understanding of its function is necessary to limit damage caused by fungal activity. All necessary methodology from chemical characterization to complete genetic analyses has been developed for medically important fungi. Now it is time to apply this knowledge to the numerous, largely aerobic and very active organisms that occupy a wide range of atmosphere-exposed habitats in the upper lithosphere. One can expect that analogies between medically- and environmentally-relevant model fungal species will help us to address the dynamics of the fungal cell EPS matrix in much more efficient and widely applicable ways.