Complex regulation of the aflatoxin biosynthesis gene cluster of Aspergillus flavus in relation to various combinations of water activity and temperature

A microarray analysis was performed to study the effect of varying combinations of water activity and temperature on the activation of aflatoxin biosynthesis genes in Aspergillus flavus grown on YES medium. Generally A. flavus showed expression of the aflatoxin biosynthetic genes at all parameter combinations tested. Certain combinations of aw and temperature, especially combinations which imposed stress on the fungus resulted in a significant reduction of the growth rate. At these conditions induction of the whole aflatoxin biosynthesis gene cluster occurred, however the produced aflatoxin B1 was low. At all other combinations (25 °C/0.95 and 0.99; 30 °C/0.95 and 0.99; 35 °C/0.95 and 0.99) a reduced basal level of cluster gene expression occurred. At these combinations a high growth rate was obtained as well as high aflatoxin production. When single genes were compared, two groups with different expression profiles in relation to water activity/temperature combinations occurred. These two groups were co-ordinately localized within the aflatoxin gene cluster. The ratio of aflR/aflJ expression was correlated with increased aflatoxin biosynthesis

Berry Phase Transition in Twisted Bilayer Graphene

The electronic dispersion of a graphene bilayer is highly dependent on rotational mismatch between layers and can be further manipulated by electrical gating. This allows for an unprecedented control over electronic properties and opens up the possibility of flexible band structure engineering. Here we present novel magnetotransport data in a twisted bilayer, crossing the energetic border between decoupled monolayers and coupled bilayer. In addition a transition in Berry phase between pi and 2pi is observed at intermediate magnetic fields. Analysis of Fermi velocities and gate induced charge carrier densities suggests an important role of strong layer asymmetry for the observed phenomena.Comment: 20 pages main paper + 10 pages supporting informatio

How does the local wind field control the aerosol distribution in coastal Dronning Maud Land?

Atmospheric circulation patterns and chemical concentrations in firn cores are highly related to each other. Atmospheric winds transport aerosols like sea salt and mineral dust over the globe and redistribute them. Because of this, it is possible to reconstruct atmospheric circulation bringing aerosol to Antarctica by analyzing chemical impurities in firn and ice. With these analyses, the gap caused by sparse atmospheric measurements can be filled and this knowledge can then be used to improve the understanding of local and global circulation patterns.Due to a very high accumulation rate (~600 kg/m²*a), coastal Dronning Maud Land (CDML) is a perfect site to conduct these studies.Here, the upper 6m of two firn cores drilled on Halvfaryggen and Sörasen (covering the time interval from 2002- 2007) were analyzed on ionic concentrations. This data was then contrasted to measurements from the air chemistry laboratories at Neumayer (NM) and Kohnenstation (KS), and synoptic measurements from automatic weather stations (distributed in CDML and at NM).The analyses show very different results: Sea salt ions (e.g. Na+) are higher correlated to ions measured in aerosol samples at the air chemistry laboratory at KS than to the one located at NM. In contrast, ions representing mineral dust (e.g. nss-Ca2+) only have a weak correlation over the whole area and time period. Accordingly, the deposition of aerosol is highly dependent on its origin and the topography in coastal Antarctica suggesting different transport pathways for sea level and higher altitude sites

Geochemistry of cold seeps - Fluid sources and systematics

Emanation of fluids at cold seeps, mud volcanoes, and other types of submarine seepage structures is a typical phenomenon occurring at continental margins worldwide. They represent pathways along which volatiles and solutes are recycled from deeply buried sediments into the global ocean, and hence they may be considered as a potentially important link in global geochemical cycles. In this contribution we present geochemical data from various geological and tectonic settings such as the Gulf of Cadiz, the convergent margin off Central America, and/or the Black Sea and provide approaches how to systemize available data sets. Clay-mineral dewatering plays a central role in terms of fluid-mobilization from greater depth, however, resulting cold seep fluids are typically very different from each other and cover a large range of geochemical signatures. This is is due to variations in control parameters such as the type and thickness of the sediment cover, thermal conditions, extension of fluid pathways, and the potential for secondary overprinting. For example, freshened fluids emanating at cold seeps off Costa Rica indicate dewatering and related geochemical reactions in subducting sediments, while fluids sampled at mud volcanoes in the Gulf of Cadiz provide evidence for a high-temperature fluid source originating in the underlying oceanic basement. The latter finding provides evidence for a hydrological connection between buried oceanic crust and the water column even at old crustal ages. Varius geochemical tracers were proposed in the past to decipher relevant processes in the subsurface. In a recent systematic study, Scholz et al. [1] demonstrated the general use of Li, reflecting the temperature-dependent isotope fractionation during early diagenetic Li uptake and burial diagenetic Li release from sediments. However, additional approaches are required in order to provide robust geochmical interpretations of cold seep fluids

The Schauinsland CO2 record: 30 years of continental observations and their implications for the variability of the European CO2 budget

Since 1972, the German Environment Agency (UBA) has been measuring continuously CO2 concentration at Schauinsland station (southwest Germany, 1205 m asl). Because of its vicinity to biogenic and anthropogenic sources and sinks, the Schauinsland CO2 record shows considerably variability. In order to remove these disturbances and derive the large-scale representative "background" CO2 levels for the respective area (southwest Germany) we perform rigorous data selection based on wind speed and time of day. During the past 30 years, the selected CO2 mixing rations increased by 1.47 ppm per year, following the mean trend in midlatitudes of the Northern Hemisphere. The average seasonal cycle (peak-to-peak) amplitude has decreased slightly from 13.8+/-0.6 ppm in the first decade (1972-1981) to 12.8 +/- 0.7 ppm in the last two decades (1982-2001). This is opposite to other northern latitude sites and is attributed to the decrease of fossil fuel CO2 emissions in the catchment area (southwest Germany and France) and its respective change in the seasonal variation. Except for May and June, monthly mean CO2 mixing ratios at Schauinsland are higher by up to 8ppm if compared to marine boundary layer air, mainly as a consequence of fossil fuel CO2 emissions in Europe. The CO2 measurements when combined with continuous 222Rn observations at the same site allow an estimate of the net CO2 flux in the catchment area of Schauinsland: mean seasonal fluxes compare very well with estimates from a process-oriented biosphere model (SIB-2) as well as from an inverse modelling approach (Peylin et al, 2000). Annual CO2 fluxes vary by more than a factor of 2, although atnthropogenic fossil fuel CO2 emissions show interannual variations of only about 10%. The major part of the variability must therefore be associated to interannual changes of biospheric uptake and release, which are on the order of the total fossil fuel emissions in the same area. This has to be taken into account when reliably quantifying and verifying the long-term carbon balance and emission reduction targets in the European Union

Carbon dioxide and methane in continental Europe: a climatology, and 222Radon-based emission estimates

4-year records of gas chromatographic carbon dioxide and methane observations from the continental mountain station Schauninsland in the Black Forest (Germany) are presented. These data are supplemented by continuous atmospheric 222Radon observations. The raw data of CO2 concentration show a large seasonal cycle of about 16ppm with monthly mean wintertime enhancements up to 10ppm higher and summer minima up to 5 ppm lower than the maritime background level in this latitude. These offsets are caused by regional and continental scale CO2 sources and sinks. The mean CH4 concentration at Schauinsland is 31ppb higher than over the Atlantic ocean, due to the European continent acting as a net source of atmospheric CH4 throughout the year. No significant seasonal cylce of methane has been observed. The long term CO2 and CH4 increase rates at Schauinsland are found to be similar to background stations in the northern hemisphere, namely 1.5 ppm CO2/yr and 8 ppb CH4/yr. On the time scale of hours and days, the wintertime concentrations of all three trace gases are highly correlated, the mean ratio of CH4/CO2 is 7.8+/-1.0ppb/ppm. The wintertime monthly mean concentrations offsets relative to the maritime background level show a CH4/CO2 ratio of 6.5+/-1.1 ppb/ppm, thus, not significantly different from the short term ratio. Using the wintertime regressions of CO2 and 222Radon respectively CH4 and 222Radon we estimate winter time CO2 flux densities of 10.4+/-4.3 mmol CO2/m2/hr (from monthly mean offsets) and 6.5+/-2.5 mmol CO2 /m2/hr (from short term fluctuations) and winter time methane flux densities of 0.066+/-0.034 mmol CH4 /m2/hr (from monthly mean offsets) and 0.057 +/-0.022 mmole CH4/m2/hr (from short term fluctuations). These flux estimates are in close agreement to CO2 respectively CH4 emission inventories reported for Germany from statistical data