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Eingeladener Vortrag
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Halophilic bacteria use a variety of osmoregulatory methods, such as the accumulation of one or more compatible solutes. The wide diversity of compounds that can act as compatible solute complicates the task of understanding the different strategies that halophilic bacteria use to cope with salt. This is specially challenging when attempting to go beyond the pathway that produces a certain compatible solute towards an understanding of how the metabolic network as a whole addresses the problem. Metabolic reconstruction based on genomic data together with Flux Balance Analysis (FBA) is a promising tool to gain insight into this problem. However, as more of these reconstructions become available, it becomes clear that processes predicted by genome annotation may not reflect the processes that are active in vivo. As a case in point, E. coli is unable to grow aerobically on citrate in spite of having all the necessary genes to do it. It has also been shown that the realization of this genetic potential into an actual capability to metabolize citrate is an extremely unlikely event under normal evolutionary conditions. Moreover, many marine bacteria seem to have the same pathways to metabolize glucose but each species uses a different one. In this work, a metabolic network inferred from genomic annotation of the halophilic bacterium Halomonas elongata and proteomic profiling experiments are used as a starting point to motivate targeted experiments in order to find out some of the defining features of the osmoregulatory strategies of this bacterium. This new information is then used to refine the network in order to describe the actual capabilities of H. elongata, rather than its genetic potential.
Mediaeval stained glass has been treated with Polymethylmetacrylate coatings by Kwiatkowski in Poland during the 1950th. Such treated panels were found in the Johannis Church of Toruń (without protective glazing), in the Cathedral of Włocławek (behind a protective glazing), and on glass kept in exhibition cases in the museum of Toruń. Surface coatings have been detected and analyzed. There was no extensive contamination by fungi or bacteria if the glass was either coated or not.
Fungal melanins are distinctive markers of rock-inhabiting ascomycetes. These complex polyphenols play important roles in stress tolerance while being essential components of fungal cell walls and useful biomarkers. Here we report signatures of melanins and carotenoids in pigment mutant strains of the black yeast Knufia petricola A95 using Raman spectroscopy
Fungal pigments such as melanin and carotenoids are distinctive markers of animal and plant pathogenic fungi as well as their environmental relatives. These complex pigments play important roles in pathogenicity and stress tolerance while also being useful as biomarkers. Accordingly, it is important to be able to identify in situ the pigments in black fungi, a group of clinical and environmental importance. In this study, wild-type and genetically modified strains of Knufia petricola A95 and wild fungal cells attached to ancient rock were investigated for their spectroscopic and microscopic Raman features and morphological appearance. Knockout mutants of melanin synthesis genes pks1 (polyketide synthase), sdh1 (scytalone dehydratase), and both pks1 and the carotenoid synthesis gene phd1 (phytoene desaturase) were studied We applied two different Raman microscopes using two lasers, with 633 nm and 488 nm wavelengths. We analyzed and compared Raman spectra between the measured reference substances and the mutant and wild-type strains. In the wild strain WT:A95, the peaks close to melanin peals were found at 1353 cm−1 and 1611 cm−1. There are no characteristic melanin peaks at 1580–1600 cm−1 and around 1350 cm−1 at the spectrum of the Δpks1/Δphd1 mutant and the Δsdh1 mutant. The Δpks1 mutant spectrum has the peaks at the beta-carotene v2 C-C in-plane stretch at 1155 cm−1 and v3 C-CH3 deformation at 1005 cm−1. The peaks of carotenoids and melanin were found in all mutants and the wild strain, except the Δpks1/Δphd1 mutant. Raman spectra allow for discrimination between the various pigments. Hence, interactions between natural fungal melanin, as well as other protective pigments, and complex environmental matrices can be characterized on a range of spatial and temporal scales.
Life on the rocks: a simple genetically tractable model system to study fungus-material interactions
(2015)
Soil formation on rock surfaces is intrinsically coupled to primary microbial colonisation of the atmosphere-lithosphere interface. Rock-inhabiting microbial life is ubiquitous but the mechanisms of biofilm establishment and more importantly, quantification of its geological input are so far only possible to be studied in simplified, well-controlled laboratory experiments. In a previous study [1] a laboratory biofilm consisting of the phototrophic cyanobacterium Nostoc punctiforme ATCC 29133 and the rock-inhabiting ascomycete Knufia petricola A95 was tested for its mineral weathering potential. Mineral dissolution was enhanced in biotic experiments as compared to abiotic ones. Here the influence of K. petricola strain A95 and a recently constructed melanin deficient mutant (A95ΔPKS) were used to study the influence of fungal pigments on weathering of forsteritic olivine. The olivine with fungal biomass was submerged in a nutrient solution (pH 6.2) in batch-reactor flasks that were incubated for 90 d at 25°C and 90 μmol photons.m2.sec-1, while shaken at 150 rpm. qPCR was used to quantify the growth of fungi. Mineral dissolution was quantified by ICP-OES analysis of the liquid medium while SEM-EDX analysis of the solid phase was used to determine secondary mineral formation and visualise growth behaviour. Wild type and mutant accelerated dissolution of the mineral: over time both release more Mg and Si from olivine than the abiotic control. Also SEM revealed a closer physical contact of the wild type cells to the mineral and a higher production of EPS of the melanin mutant A95ΔPKS. This important difference in the ability of the wild type strain to adhere to the mineral surface might be crucial in maintaining a biologically modified environment. This biologically engineered habitat serves as a place where mineral dissolution as well as deposition of metabolic products (EPS + pigments) can impact the rock surface. We expect this study to increase the awareness on the impact of microbiology, and more specifically, rock-inhabiting fungi on mineral weathering. [1] Seiffert, F., Bouchez, J., von Blanckenburg, F., and Gorbushina, A. A. (2014). Microbial colonization of bare rocks: laboratory biofilm enhances mineral weathering. Proc. Earth Plan. Sci. 12,123–129.doi: 10.1016/j.proeps.2014.08.042
Many microorganisms including free-living and symbiotic fungi weather minerals through the formation of biofilms on their surface. Weathering thus proceeds not only according to the mineral’s chemistry and the environmental conditions but also according to the local biofilm chemistry. These processes can be dissected in experiments with defined environmental settings and by employing genetic tools to modify traits of the fungal biofilm. Biofilms of the rock-inhabiting fungus Knufia petricola strain A95 (wild-type, WT) and its melanin-deficient mutant (ΔKppks) were grown on polished olivine sections in subaerial (air-exposed) and subaquatic (submerged) conditions. After seven months of interaction at pH 6 and 25°C, the fungus-mineral interface and abiotic olivine surface were compared using high resolution transmission electron microscopy (HRTEM). The abiotic, subaquatic olivine section showed a 25 nm thick, continuous amorphous layer, enriched in Fe and depleted in Si compared to the underlying crystalline olivine. This amorphous layer formed either through a coupled interfacial dissolution reprecipitation mechanism or through the adsorption of silicic acid on precipitated ferric hydroxides. Its thickness was likely enhanced by mechanical stresses of polishing. Directly underneath a fungal biofilm (WT and mutant alike), the surface remained mostly crystalline and was strongly etched and weathered, indicating enhanced olivine dissolution. The correlation between enhanced olivine dissolution and the absence of a continuous amorphous layer is a strong indication of the dissolution-inhibiting qualities of the latter. We propose that the fungal biofilm sequesters significant amounts of Fe, preventing formation of the amorphous layer and driving olivine dissolution onwards. The seemingly similar olivine surface underneath both WT and mutant biofilms illustrates the comparably insignificant role of specific biofilm traits in the weathering of olivine once biofilm attachment is imposed. Under subaerial conditions, the absence of water on the abiotic surface prohibited olivine dissolution. This was overcome by the water retention capacities of both the WT and mutant biofilm: the olivine surface underneath subaerial fungal biofilms was as weathered as the corresponding subaquatic olivine surface. Under the studied environmental settings, the effect of fungal biofilms on olivine weathering seems to be universal, independent of the production of melanin, the composition of extracellular polymeric substances (EPS) or air-exposure.
Genetics for geomycology
(2017)
Black microcolonial fungi (MCF) are persistent inhabitants of rock surfaces. Biofilm establishment and more importantly, quantification of its geological input are so far only possible to be studied in simplified, well-controlled laboratory experiments. Therefore, the ability of MCF to cope with multiple, rapidly fluctuating stresses makes the group an interesting subject in the study of stress resistance but also in mineral weathering processes. We studied the role of protective pigments in stress resistance and mineral weathering of the rock-inhabiting fungus Knufia petricola (Chaetothyriales) strain A95.