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Eingeladener Vortrag
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Rock weathering is a key process in global elemental cycling. Life participates in this process with tangible consequences observed from the mineral interface to the planetary scale. Multiple lines of evidence show that microorganisms may play a pivotal—yet overlooked—role in weathering. This topic is reviewed here with an emphasis on the following questions that remain unanswered: What is the quantitative contribution of bacteria and fungi to weathering? What are the associated mechanisms and do they leave characteristic imprints on mineral surfaces or in the geological record? Does biogenic weathering fulfill an ecological function, or does it occur as a side effect of unrelated metabolic functions and biological processes? An overview of efforts to integrate the contribution of living organisms into reactive transport models is provided. We also highlight prospective opportunities to harness microbial weathering in order to support sustainable agroforestry practices and mining activities, soil remediation, and carbon sequestration.
Sol-gel synthesis was used to prepare nanoparticles of MgF2 and CaF2. These nanoparticles were tested for their application in wood protection. In comparison to control samples, wood specimens treated with MgF2 and CaF2 showed lower mass loss under exposure to termites and fungi. Samples treated with MgF2 performed better at protecting wood from cellulose degradation when exposed to termites. Conversely, in the presence of fungi, mass loss in treated samples was similar irrespective of the chemical composition (MgF2 and CaF2) of the treatment. A possible explanation for this difference in results between termites and fungi could be their different mechanism of cellulose hydrolysis. Thus, future wood preservatives would need to be customized according to their specific application.
In this study, nanoscopic particles of magnesium Fluoride (MgF2) and calcium fluoride (CaF2) also known as nano metal fluorides (NMFs), were evaluated for their potential to improve wood durability. Even though these fluorides are sparingly soluble, their synthesis in the form of nano-sized particles turns them into promising candidates for wood preservation. Their distinct property of low-water solubility is proposed to maintain long-lasting protection of treated wood by reducing the leaching of fluoride. Analytical methods were used to characterize the synthesized NMFs and their distribution in treated wood specimens. Transmission electron microscopy images showed that these fluoride particles are smaller than 10 nm. In nano metal fluoride (NMF) treated specimens, aggregates of these particles are uniformly distributed in the wood matrix as confirmed with scanning electron microscopy images and their corresponding energy-dispersive X-ray spectroscopy maps. The fluoride aggregates form a protective layer around the tracheid walls and block the bordered pits, thus reducing the possible flow path for water absorption into wood. This is reflected in the reduced swelling and increased hydrophobicity of wood treated with NMFs. The biocidal efficacy of NMFs was tested against brown-rot fungi (Coniophora puteanaand Rhodonia placenta), white-rot fungus (Trametes versicolor), and termites (Coptotermes formosanus). The fungal and termite tests were performed in accordance with the EN 113 (1996) and EN 117 (2012) standards, respectively. Prior to fungal tests, the NMF treated wood specimens were leached according to the EN 84 (1997)standard. Compared to untreated specimens, the NMF treated wood specimens have a higher resistance to decay caused by brown-rot fungi, white-rot fungus, and termites. Although all NMF treatments in wood reduce the mass loss caused by fungal decay, only the combined treatment of MgF2 and CaF2 has efficacy against both brown-rot fungi and white-rot fungus. Similarly, wood treated with the combined NMF formulation is the least susceptible to attack by C. formosanus.It is proposed that combining MgF2 and CaF2changes their overall solubility to promote the release of fluoride ions at the optimal concentration needed for biocidal efficacy against fungi and termites. In this thesis, it was proven that even after leaching, sufficient fluoride was present to protect NMF treated wood from fungal decay. This shows that NMFs are robust enough for above ground contact outdoor applications of wood, where permanent wetness cannot be avoided according to Use Class 3.2, as per the EN 335 (2013) standard. Also, they pose a low risk to human health and the environment because they are sparingly soluble. Since NMFs significantly reduce the decay of wood, the CO2 fixed in it will be retained for longer than in unpreserved wood. Overall, the novel results of this study show the potential of NMFs to increase the service life of building materials made from non-durable wood.
The microbial contamination of fuels by fungi or bacteria presents risks such as corrosion and fuel system fouling, which can produce critical problems in refineries and distribution systems and has a significant economic impact at every phase of the process. Many factors have been cited as responsible for microbial growth, like the presence of water in the storage tanks. Indeed, only 1 % water in a storage system is enough for the growth of microorganisms like bacteria or yeasts, as well as for the development of fungal biomass at the oil/water interface.1
In this work, a rapid test for the accurate determination of genomic DNA from aqueous fuel extracts is presented. The detection is based on the employment of polystyrene-mesoporous silica core-shell particles, on which modified fluorescent molecular beacons are covalently grafted. Those beacons incorporate in the hairpin loop a target sequence highly conserved in all bacteria, corresponding to a fragment of the 16S ribosomal RNA subunit. The designed single-stranded molecular beacon contained fluorescein as an internal indicator and a quencher in its proximity when not hybridized. Upon hybridization in presence of the target sequence, the indicator and the quencher are spatially separated, resulting in fluorescence enhancement. To perform the assay the designed particles were disposed on different glass fiber strips to try to achieve a portable and sensitive rapid test. Assays showed that presence of genomic DNA extracts from bacteria down to 50–70 μg L-1 induces a fluorescence response. The optical read-out was adapted for on-site monitoring by adapting a 3D-printed case on a conventional smartphone, taking advantages of the CMOS detector sensitivity.2 Such embedded assembly allowed to detect genomic DNA in aqueous extracts down to the mg L-1 range and presents an interesting step toward on-site monitoring of fuel contamination.
Honeybee symbionts, predominantly bacteria, play important roles in honeybee health, nutrition, and pathogen protection, thereby supporting colony health. On the other hand, fungi are often considered indicators of poor bee health, and honeybee microbiome studies generally exclude fungi and yeasts. We hypothesized that yeasts may be an important aspect of early honeybee biology, and if yeasts provide a mutual benefit to their hosts, then honeybees could provide a refuge during metamorphosis to ensure the presence of yeasts at emergence. We surveyed for yeast and fungi during pupal development and metamorphosis in worker bees using fungal-specific quantitative polymerase chain reaction (qPCR), next-generation sequencing, and standard microbiological culturing. On the basis of yeast presence in three distinct apiaries and multiple developmental stages, we conclude that yeasts can survive through metamorphosis and in naïve worker bees, albeit at relatively low levels. In comparison, known bacterial mutualists, like Gilliamella and Snodgrassella, were generally not found in pre-eclosed adult bees. Whether yeasts are actively retained as an important part of the bee microbiota or are passively propagating in the colony remains unknown. Our demonstration of the constancy of yeasts throughout development provides a framework to further understand the honeybee microbiota.
Biological testing of wood
(2006)
Microbial colonization affects the efficiency of photovoltaic panels in a tropical environment
(2015)
Sub-aerial biofilm (SAB) development on solar panels was studied in São Paulo. After 6, 12 and 18 months' exposure, photovoltaic panels were covered by increasing proportions of organic matter (42%, 53% and 58%, respectively). Fungi were an important component of these biofilms; very few phototrophs were found. Major microorganisms detected were melanised meristematic ascomycetes and pigmented bacterial genera Arthrobacter and Tetracoccus. While diverse algae, cyanobacteria and bacteria were identified in biofilms at 6 and 12 months, diversity at a later stage was reduced to that typical for SAB: the only fungal group detected in 18 month biofilm was the meristematic Dothideomycetes and the only phototrophs Ulothrix and Chlorella. Photovoltaic modules showed significant power reductions after 6, 12 (both 7%) and 18 (11%) months. The lack of difference in power reduction between 6 and 12 months reflects the dual nature of soiling, which can result from the deposition of particulates as well as from SAB fouling. Although 12-month old SAB demonstrated an almost 10-fold increase in fungal colonization and a higher organic content, the larger non-microbial particles (above 10 µm), which were important for efficiency reduction of lightly-biofilmed panels, were removed by high rainfall just before the 12-month sampling.
Fungi that share light-flooded habitats with phototrophs may profit from their excess photosynthetic products. Sunlight-associated stresses are however multiple: high temperatures, UV radiation with associated DNA damage, accumulation of reactive oxygen species (ROS), desiccation and osmotic stresses. Ascomycota dominating light-flooded habitats accurately sense and respond to changes in light using it as a cue to coordinate growth, stress responses as well as to establish pathogenic or symbiotic relationships. Two species from two light-flooded habitats – phyllosphere and sun-exposed solid surfaces – were analysed for their photoreceptor distribution.
In both habitats phototroph-associated and black [dihydroxynaphthalene (DHN) melanin-containing] fungi are prevalent. This diversity was sampled with the plant-associated fungus Botrytis cinerea (Leotiomycetes), while Knufia petricola (Eurotiomycetes) was included as a typical biofilm-former on sun-exposed solid surfaces e.g. rocks, building facades, roofs, and solar panels. The analysis has shown that genomes of black fungi contain more photoreceptors than animal pathogens and saprophytes such as Aspergillus nidulans and Neurospora crassa1,2. B. cinerea that causes the grey mould disease by infecting the above-ground parts of more than 200 dicots has a highly sophisticated photosensory and signalling system that helps to avoid light and to locate susceptible hosts1.
Rock-inhabiting Dothideomycetes and Eurotiomycetes including Knufia petricola possess equal numbers of photoreceptors along with the same set of protective metabolites i.e. melanin, carotenoids and mycosporines2. This similarity between black fungi from plant and rock surfaces suggests that photoperception and -regulation are important for sun-stressed fungi that receive nutrients through cooperation with phototrophs. CRISPR/Cas9-based genetic tools for manipulating K. petricola were established3 and are currently used for elucidating the functions of the different photoreceptors in the biology of rock-inhabiting fungi.
This work was supported by the grant SCHU 2833/4-1 from the German Research Foundation (DFG) and internal funds of the BAM.
Fungi that share light-flooded habitats with phototrophs may profit from excess photosynthetic products. But to cope with sunlight-associated stresses it is important for fungi to accurately sense and respond to changes in light. To test the hypothesis that light is an environmental cue that Ascomycota use to coordinate growth, stress responses as well as to establish pathogenic or symbiotic relationships, the photoreceptor (PR) distribution in species from different ecological niches was analysed. The genomes of black fungi from phyllosphere and exposed solid surfaces contain multiple photoreceptors (PRs). The filamentous foliar plant pathogen Botrytis cinerea (Leotiomycetes) has a highly sophisticated photosensory and signalling system that helps to avoid light and to locate susceptible hosts. Rock-inhabiting Dothideo- and Eurotiomycetes including Knufia petricola possess equal numbers of PRs along with the same set of protective pigments. This similarity between black fungi from plant and rock surfaces suggests that photoperception and photoregulation are important for fungi that avoid loss of energy and nutrients through cooperation with phototrophs.