The infectious propagules of Aspergillus fumigatus are coated with antimicrobial peptides

Fungal spores are unique cells that mediate dispersal and survival in the environment. For pathogenic fungi encountering a susceptible host, these specialised structures may serve as infectious particles. The main causative agent of the opportunistic disease aspergillosis, Aspergillus fumigatus, produces asexual spores, the conidia, that become dissipated by air flows or water currents but also serve as propagules to infect a susceptible host. We demonstrate that the defX gene of this mould encodes putative antimicrobial peptides resembling cysteine‐stabilised (CS)$_{αβ}$ defensins that are expressed in a specific spatial and temporal manner in the course of asexual spore formation. Localisation studies on strains expressing a fluorescent proxy or tagged defX alleles expose that these antimicrobial peptides are secreted to coat the conidial surface. Deletion mutants reveal that the spore‐associated defX gene products delay the growth of Gram‐positive Staphylococcus aureus and demonstrate that the defX gene and presumably its encoded spore‐associated defensins confer a growth advantage to the fungal opponent over bacterial competitors. These findings have implications with respect to the ecological niche of A. fumigatus that serves as a ‘virulence school’ for this human pathogenic mould; further relevance is given for the infectious process resulting in aspergillosis, considering competition with the host microbiome or co‐infecting microorganisms to break colonisation resistance at host surfaces

Uncoupling human and climate drivers of late Holocene vegetation change in southern Brazil

In the highlands of southern Brazil an anthropogenitcally driven expansion of forest occurred at the expense of grasslands between 1410 and 900cal BP, coincident with a period of demographic and cultural change in the region. Previous studies have debated the relative contributions of increasing wetter and warmer climate conditions and human landscape modifcations to forest expansion, but generally lacked high resoltiuon proxies to measure these efects, or have relied on single proxies to reconstruct both climate and vegetation. Here, we develop and test a model of natural ecosystem distribution against vegetation histories, paleoclimate proxies, and the archaeological record to distinguish human from temperature and precipitation impacts on the distribution and expansion of Araucaria forests during the late Holocene. Carbon isotopes from soil profles confrm that in spite of climatic fuctuations, vegetation was stable and forests were spatially limited to south-facing slopes in the absence of human inputs. In contrast, forest management strategies for the past 1400 years expanded this economically important forest beyond its natural geographic boundaries in areas of dense pre-Columbian occupation, suggesting that landscape modifcations were linked to demographic changes, the efects of which are still visible today

Links between composition of heavy organo-mineral fractions and forest expansion on grassland with long-term fire history

Comunicación oral S25.B.03, sesión S25 Memory Function of Recent and Paleosoils, dentro del capítulo Symposia.-- Congreso celebrado del 25-29 de agosto 2008, en Viena, Austria.Peer reviewe

Carbon isotope studies and lignin analysis of plants and soil organic matter detect vegetation changes in the southern Brazilian highlands

Comunicación oral SSS29-1TU4O-002, presentada en la Sesión SSS29 Molecular biogeochemistry: the fate of organic carbon in soils.-- Congreso celebrado del 13-18 de abril 2008, en Viena, Austria.The isotopic and biochemical composition of plants, organic surface layers and humic substances from 13 soils was characterized to discover the origin of the present mosaic of grassland (C4) and Araucaria forest (C3). The bulk soils were seperated into light and heavy fractions by density fractionation. 14C dating and 13C values reflect a chronosequence of Araucaria forest expansion on grassland which started after 1300 yr BP.Peer reviewe

Evaluating pore structures of soil components with a combination of "conventional" and hyperpolarised 129Xe NMR studies

129Xe nuclear magnetic resonance (NMR) spectroscopic studies of xenon gas adsorbed on model systems representing soil porous components (Al (hyrd)oxides and charcoals) as well as natural soil materials (derived from a non-allophanic Andosol) were performed with the aim of characterising their micro- (empty> pores and pores coated with organic species. In AlOOH, an interconnected system of micro- and mesopores was tested. The enhanced sensitivity of HP 129Xe NMR allowed us detecting micropores in charcoals, where N2 adsorption method underestimated porosity due to the restricted N2 diffusion at 77K. The interconnected pore structure of charcoals was attributed to the voids formed by both polyaromatic and aliphatic domains (evidenced by 13C NMR). The observed differences between the TP- and HP 129Xe NMR patterns were explained by the restricted xenon diffusion through charcoal particles caused by the constricted pore openings. Their suggested size is of the order of one or two diameters of the Xe atom. For the Andosol clay fractions, the large low-field 129Xe shifts (up to 175ppm) increasing with Xe pressure indicated a developed porosity most obviously comprised by the interconnected micro- and mesopores. Such porous network may originate from the >multi-domain> structure of soil clay particles, i.e. particles formed by agglomerated nano-sized crystallites. The latter are assumed to be the polynuclear Alx(H2O)y(OH)z clusters formed by hydrolysis reactions of Al3+ species after the destroying of Al-humus complexes by the H2O2-oxidation. © 2011 Elsevier B.V.Peer Reviewe