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Rock-inhabiting black fungi [also microcolonial or meristematic fungi (MCF)] are a phylogenetically diverse group of melanised ascomycetes with distinctive morphological features that confer extensive stress tolerance and permit survival in hostile environments. The MCF strain A95 Knufia petricola (syn. Sarcinomyces petricola) belongs to an ancestral lineage of the order Chaetothyriales (class Eurotiomycetes). K. petricola strain A95 is a rock-inhabiting MCF and its growth requirements were studied using the 96-well plate-based Biolog System under ~1070 different conditions (osmotic stress, pH growth optima, growth factor requirements and nutrient catabolism). A95 is an osmotolerant, oligotrophic MCF that grows best around pH 5. Remarkably, A95 shows metabolic activity in the absence of added nitrogen, phosphorus or sulphur. Correlations could be drawn between the known nutrient requirements of A95 and what probably is available in sub-aerial systems (rock and other material surfaces). Detailed knowledge of A95's metabolic requirements allowed formulation of a synthetic medium that supports strong fungal growth.
Black fungi are recently described microorganisms and amongst the most stress-tolerant eukaryotes currently known. They are a taxonomically diverse, but morphologically similar group of filamentous fungi that share two distinct signature characteristics, i.e. melanisation of the cell wall and compact colony morphology, which confer them passive, constituent extremotolerance. Albeit morphologically undifferentiated, black fungi show extensive phylogenetic and ecological diversity. Due to their persistence in unfavourable niches, they are ubiquitous on deserts and in glaciers and are permanent settlers of rock and other atmosphere-exposed material surfaces as well as man-made environments like salterns, humidifiers and dishwashers, and thus widespread in temperate regions worldwide. Some members are devastating opportunistic pathogens of invertebrates or vertebrates, including humans; others show symbiotic potentials with co-occurring microorganisms in extreme ecosystems. Beside their interest for fundamental biology, black fungi are important for several applied applications, e.g. in biotechnology, astrobiology, bioremediation and material preservation. Despite recent advances in the study of these fungi, many biological questions remain to be clarified regarding the molecular mechanisms underlying persistence, their physiology and nutritional modes, and their specific interactions with putative symbiotic partners. Models for pathogenic and halotolerant black fungi are established; however, no model was yet available for rock- and material-inhabiting ones. This thesis introduces the strain Knufia petricola A95 as a suitable model to study rockinhabiting lifestyle. For this purpose, the strain was characterised at the physiological and molecular levels by phenotype microarrays, growth experiments and genome analyses as well as further methods. Cell- wall mutants of K. petricola A95 isolated during the course of this study were described and included in the comparative analysis to investigate effect of melanisation on physiology and stress tolerance. Direct comparisons were also performed between the model strain and the phylogenetically distant but ecologically, biogeographically and morphologically highly similar rock inhabitant Coniosporium apollinis. Preliminary observations of a model biofilm of K. petricola A95 and the photosynthetic cyanobacterium Nostoc punctiforme ATCC 29133 are introduced to study symbiotic interactions of rock-inhabiting microorganisms. Data presented here are a contribution to the understanding of ecophysiology and extremotolerance of rock-inhabiting black fungi.