Land-use intensification systematically alters the size structure of aquatic communities in the Neotropics

Land-use and land-cover transitions can affect biodiversity and ecosystem functioning in a myriad of ways, including how energy is transferred within food-webs. Size spectra (i.e. relationships between body size and biomass or abundance) provide a means to assess how food-webs respond to environmental stressors by depicting how energy is transferred from small to larger organisms. Here, we investigated changes in the size spectrum of aquatic macroinvertebrates along a broad land-use intensification gradient (from Atlantic Forest to mechanized agriculture) in 30 Brazilian streams. We expected to find a steeper size spectrum slope and lower total biomass in more disturbed streams due to higher energetic expenditure in physiologically stressful conditions, which has a disproportionate impact on large individuals. As expected, we found that more disturbed streams had fewer small organisms than pristine forest streams, but, surprisingly, they had shallower size spectrum slopes, which indicates that energy might be transferred more efficiently in disturbed streams. Disturbed streams were also less taxonomically diverse, suggesting that the potentially higher energy transfer in these webs might be channelled via a few efficient trophic links. However, because total biomass was higher in pristine streams, these sites still supported a greater number of larger organisms and longer food chains (i.e. larger size range). Our results indicate that land-use intensification decreases ecosystem stability and enhances vulnerability to population extinctions by reducing the possible energetic pathways while enhancing efficiency between the remaining food-web linkages. Our study represents a step forward in understanding how land-use intensification affects trophic interactions and ecosystem functioning in aquatic systems.     

Invasive potential of golden and zebra mussels in present and future climatic scenarios in the new world

Hydrobiologia - Biological invasions and climate change are important drivers of biodiversity loss. In freshwater ecosystems, golden and zebra mussels are two highly aggressive invasive species...     

Twelve testable hypotheses on the geobiology of weathering

Critical Zone (CZ) research investigates the chemical, physical, and biological processes that modulate the Earth's surface. Here, we advance 12 hypotheses that must be tested to improve our understanding of the CZ: (1) Solar-to-chemical conversion of energy by plants regulates flows of carbon, water, and nutrients through plant-microbe soil networks, thereby controlling the location and extent of biological weathering. (2) Biological stoichiometry drives changes in mineral stoichiometry and distribution through weathering. (3) On landscapes experiencing little erosion, biology drives weathering during initial succession, whereas weathering drives biology over the long term. (4) In eroding landscapes, weathering-front advance at depth is coupled to surface denudation via biotic processes. (5) Biology shapes the topography of the Critical Zone. (6) The impact of climate forcing on denudation rates in natural systems can be predicted from models incorporating biogeochemical reaction rates and geomorphological transport laws. (7) Rising global temperatures will increase carbon losses from the Critical Zone. (8) Rising atmospheric P(CO2) will increase rates and extents of mineral weathering in soils. (9) Riverine solute fluxes will respond to changes in climate primarily due to changes in water fluxes and secondarily through changes in biologically mediated weathering. (10) Land use change will impact Critical Zone processes and exports more than climate change. (11) In many severely altered settings, restoration of hydrological processes is possible in decades or less, whereas restoration of biodiversity and biogeochemical processes requires longer timescales. (12) Biogeochemical properties impart thresholds or tipping points beyond which rapid and irreversible losses of ecosystem health, function, and services can occur.     

Aerosols transmit prions to immunocompetent and immunodeficient mice

Prions, the agents causing transmissible spongiform encephalopathies, colonize the brain of hosts after oral, parenteral, intralingual, or even transdermal uptake. However, prions are not generally considered to be airborne. Here we report that inbred and crossbred wild-type mice, as well as tga20 transgenic mice overexpressing PrP(C), efficiently develop scrapie upon exposure to aerosolized prions. NSE-PrP transgenic mice, which express PrP(C) selectively in neurons, were also susceptible to airborne prions. Aerogenic infection occurred also in mice lacking B- and T-lymphocytes, NK-cells, follicular dendritic cells or complement components. Brains of diseased mice contained PrP(Sc) and transmitted scrapie when inoculated into further mice. We conclude that aerogenic exposure to prions is very efficacious and can lead to direct invasion of neural pathways without an obligatory replicative phase in lymphoid organs. This previously unappreciated risk for airborne prion transmission may warrant re-thinking on prion biosafety guidelines in research and diagnostic laboratories.     

Structural Organization of Mammalian Prions as Probed by Limited Proteolysis

Elucidation of the structure of PrP^Sc continues to be one major challenge in prion research. The mechanism of propagation of these infectious agents will not be understood until their structure is solved. Given that high resolution techniques such as NMR or X-ray crystallography cannot be used, a number of lower resolution analytical approaches have been attempted. Thus, limited proteolysis has been successfully used to pinpoint flexible regions within prion multimers (PrP^Sc). However, the presence of covalently attached sugar antennae and glycosylphosphatidylinositol (GPI) moieties makes mass spectrometry-based analysis impractical. In order to surmount these difficulties we analyzed PrP^Sc from transgenic mice expressing prion protein (PrP) lacking the GPI membrane anchor. Such animals produce prions that are devoid of the GPI anchor and sugar antennae, and, thereby, permit the detection and location of flexible, proteinase K (PK) susceptible regions by Western blot and mass spectrometry-based analysis. GPI-less PrP^Sc samples were digested with PK. PK-resistant peptides were identified, and found to correspond to molecules cleaved at positions 81, 85, 89, 116, 118, 133, 134, 141, 152, 153, 162, 169 and 179. The first 10 peptides (to position 153), match very well with PK cleavage sites we previously identified in wild type PrP^Sc. These results reinforce the hypothesis that the structure of PrP^Sc consists of a series of highly PK-resistant β-sheet strands connected by short flexible PK-sensitive loops and turns. A sizeable C-terminal stretch of PrP^Sc is highly resistant to PK and therefore perhaps also contains β-sheet secondary structure.     

Induction and functional role of cytochromes P450 in the filamentous fungi Mortierella alpina ATCC 8979 and Cunninghamella blakesleeana DSM 1906 during hydroxylation of cycloalkylbenzoxazoles

The occurrence and regulation of cytochrome P450 (P450) in Mortierella alpina and Cunninghamella blakesleeana have been studied to elucidate the enzymatic basis by which 2-cyclopentyl-1,3-benzoxazole is hydroxylated to 3-(benz-1,3-oxazol-2-yl)cyclopentan-1-ol by these organisms. The occurrence of P450 in M. alpina was first been shown after induction with n-hexane. An assay protocol was developed with n-hexane-induced cells and adapted to the handling of fungal mycelia. This allowed the direct spectral determination of P450 in non-fractionated whole-cell suspensions, and an investigation of its regulation. Small amounts of P450 have been detected in early-stationary-phase cells in the absence of exogenous inducers. Addition of 2-cyclopentyl-1,3-benzoxazole or n-hexane resulted in a significant induction of P450. Induction by n-hexane occurs in all phases of growth but decreases rapidly during the stationary phase. The rate of 2-cyclopentyl-1,3-benzoxazole hydroxylation correlated with the content of substrate-induced P450 but not with the level of n-hexane-induced P450. Hydroxylation rates were significantly diminished in the presence of typical P450 inhibitors, the interaction of which with P450 was shown with isolated microsomes of M. alpina. It is concluded that a P450 enzyme is responsible for the hydroxylation of 2-cyclopentyl-1,3-benzoxazole, but that multiple forms of P450 forms occur. Similarly, a dependence on P450 is shown by spectral as well as by inhibition studies for the hydroxylation of this substrate by C. blakesleeana. Received: 18 August 1998 / Received revision: 23 November 1998 / Accepted: 29 November 1998     

Nuclear magnetic resonance signal assignments of purified [13C]methyl-enriched yeast phenylalanine transfer ribonucleic acid

Yeast tRNA Phe, enriched in carbon-13 specifically at the naturally occurring methyl groups, has been produced through biosynthesis, then purified, and analyzed. Transfer RNA Phe was purified from the [13C]methyl-enriched, unfractionated tRNA that had been extracted from a methionine auxotroph of Saccharomyces cerevisiae [Agris, P. F., Kovacs, S. A. H., Smith, C., Kopper, R. H., & Schmidt, P. G. (1983) Biochemistry 22, 1402-1408]. The yeast had been grown in minimal medium supplemented with [13C]methylmethionine. Transfer RNA Phe purity and the full extent of nucleoside modification were confirmed by high-performance liquid chromatography of constituent nucleosides with simultaneous UV spectral identification and quantitation. Mass spectometry of [13C]methyl-enriched nucleosides and NMR of the tRNA indicated an enrichment of at least 70 atom %. Twelve resolved and prominent carbon-13 NMR signals from the tRNA were seen between 10 and 60 ppm. These have been assigned to 13 of the 14 naturally occurring methyl groups. However, the partially resolved signals assigned to the two 5-methylcytidines could not be assigned to their specific nucleoside positions of either 40 or 49 in the molecule. In addition, the partially resolved signals of the two methyl esters of wybutosine could not be distinguished. The methyl group found not to be enriched with 13C is bound to the ring carbon in the hypermodified nucleoside wybutosine (Y). A 13th enriched signal downfield (120.9 ppm) has been assigned to one of the two carbons added to guanosine to form the third ring in the biosynthesis of Y. The 13C enrichment of this ring carbon demonstrates its origin from the methionine methyl group.(ABSTRACT TRUNCATED AT 250 WORDS)