Solar energy has been transformed into useful redox differences or disequilibria within the Earth´s crust since the onset of anoxygenic and oxygenic photosynthesis in the Precambrian. Inorganic oxidized carbon is transformed into reduced carbon compounds by capturing and storing solar energy. During this process, many different organic compounds are formed including carbohydrates, proteins, hydrocarbons, and various other complex organic metabolic products and their diagenetic polymerization products (melanin, humic substances, petroleum, coal, and kerogen). Many of these solar energy-enriched compounds, however, are oxidized immediately or during the diagenetic transformation of sediments. The oxidation agents are oxygen, sulfate, iron, and other oxidized compounds, which in turn are partly enriched with the original solar energy. On a global biogeochemical scale, however, sulfur and iron are the most important elements. Geological evidence shows that biogeochemical cycles tend to yield stable ratios between the most oxidized forms of carbon (carbon dioxide and calcium/magnesium carbonate) and the most reduced forms (diamond, coal, methane, and hydrocarbons). Throughout the Earths history and evolution, this equilibrium ratio is around 1:4, maximally 1:5. When too much carbon is stored in the crust in the form of reduced compounds or vice versa, climatic and biogeomorphogenetic consequences upset the equilibrium. The biosphere reacts in a way to return to the optimal ratio. Excellent examples for this fluctuating equilibrium are the Carboniferous (too much organic carbon stored), the Permian (too little organic carbon stored), and the Tertiary with a generally equivalent production of hydrocarbons and carbonates. At present, we are in a period in which there is a global biogeochemical need to oxidize reduced carbon compounds as fast as possible in order to avoid even more dramatic global climate shifts. The highly evolved human genome seems to be the tool for this shift. Enormous amounts of reduced carbon are turned into the oxidized form as carbon dioxide, which by various biogeochemical pathways is quickly transformed into carbonate, another oxidized form of carbon that can be stabilized and stored in the sedimentary record. Fast recycling of excessively stored solar energy may enable the survival of a global biosphere under highly stressed conditions.
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.
Morphologically simple and microbially dominated ecosystems termed “biofilms” have existed on Earth for a long period of biosphere evolution. A model biofilm combining one heterotroph and one phototroph component was used in a laboratory experiment to simulate biogenic weathering with two different specimens of basic rock samples from the soil profiles. The rocks fragments from the regions of cold environments of Eurasia,where abiotic physical processes, including rock disintegration initiated by freezing–thawing cycles, represent the most probable Scenario of rock weathering, were subjected to biological colonization. The rock Fragments were represented by dolerite and metagabbro amphibolites. Polished sections of the rock samples were inoculated with the model microbiological consortium of the oligotrophic fungus and the phototrophic cyanobacteria (biofilm). After 3 month runtime of the experiment the progress of rock weathering was derived from the growth of the biofilm on the rock surfaces. The model biofilm visualization on the rock surface of polished sections illustrated their stronger development namely on dolerite in comparison with metagabbro amphibolite. The findings confirmed the higher sensitivity of dolerite to biogenic weathering due to (i) mineral association, in which quartz was absent and (ii) porosity providing higher specific surface area for biotic—abiotic interaction influenced by the occurrence of micro-porosity in the rock.
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.