Differential responses of freshwater wetland soils to sulphate pollution

Sulphate (SO₄ ^2-)reduction rates are generally low in freshwaterwetlands and are regulated by the scarceavailability of the ion. Increasedconcentrations of this electron acceptor due tosulphur (S) pollution of groundwater andsurface water may, however, lead to highSO₄ ^2- reduction rates now regulatedby the availability of appropriate electrondonors. Due to variations in this availability,the response to S pollution (e.g. from surfacewater or groundwater) is expected to differbetween soils. This hypothesis was tested inlaboratory mesocosm experiments by comparingtwo wetland soil types with distinctlydifferent humus profiles: a Hydromoder and aRhizomull type. In the first type, expected tohave a higher availability of degradable soilorganic matter (SOM), SO₄ ^2-availability appeared to be rate limiting forSO₄ ^2- reduction. In the Rhizomullsoils, in contrast, the electron acceptor didnot limit SO₄ ^2- reduction rates athigher concentrations. These differences inresponse could not, however, be attributed todifferences in the various SOM fractions or inSOM densities. Eutrophication and free sulphideaccumulation, two major biogeochemical problemscaused by SO₄ ^2- pollution, occurredin both types. The absolute extent ofphosphorus mobilisation was determined by theconcentration of this element in the soil (C/Pratio), while the level of sulphideaccumulation was governed by the concentrationof dissolved iron in the pore water. It wastherefore concluded that neither the humusprofile nor the concentrations of different SOMfractions in the soils are reliable indicatorsfor the sensitivity of wetland types to Spollution.     

Process monitoring of virus-like particle reassembly by diafiltration with UV/Vis spectroscopy and light scattering

Virus-like particles (VLPs) have shown great potential as biopharmaceuticals in the market and in clinics. Nonenveloped, in vivo assembled VLPs are typically disassembled and reassembled in vitro to improve particle stability, homogeneity, and immunogenicity. At the industrial scale, cross-flow filtration (CFF) is the method of choice for performing reassembly by diafiltration. Here, we developed an experimental CFF setup with an on-line measurement loop for the implementation of process analytical technology (PAT). The measurement loop included an ultraviolet and visible (UV/Vis) spectrometer as well as a light scattering photometer. These sensors allowed for monitoring protein concentration, protein tertiary structure, and protein quaternary structure. The experimental setup was tested with three Hepatitis B core Antigen (HBcAg) variants. With each variant, three reassembly processes were performed at different transmembrane pressures (TMPs). While light scattering provided information on the assembly progress, UV/Vis allowed for monitoring the protein concentration and the rate of VLP assembly based on the microenvironment of Tyrosine-132. VLP formation was verified by off-line dynamic light scattering (DLS) and transmission electron microscopy (TEM). Furthermore, the experimental results provided evidence of aggregate-related assembly inhibition and showed that off-line size-exclusion chromatography does not provide a complete picture of the particle content. Finally, a Partial-Least Squares (PLS) model was calibrated to predict VLP concentrations in the process solution. values of 0.947–0.984 were reached for the three HBcAg variants. In summary, the proposed experimental setup provides a powerful platform for developing and monitoring VLP reassembly steps by CFF.     

Prescribing diatom morphology: toward genetic engineering of biological nanomaterials

The formation of inorganic materials with complex form is a widespread biological phenomenon (biomineralization). Among the most spectacular examples of biomineralization is the production by diatoms (a group of eukaryotic microalgae) of intricately nanopatterned to micropatterned cell walls made of silica (SiO2). Understanding the molecular mechanisms of diatom silica biomineralization is not only a fundamental biological problem, but also of great interest in materials engineering, as the biological self-assembly of three-dimensional (3D) inorganic nanomaterials has no man-made analog. Recently, insight into the molecular mechanism of diatom silica formation has been obtained by structural and functional analysis of biomolecules that are involved in this process. Furthermore, the rapid development of diatom molecular genetics has provided new tools for investigating the silica forming machinery of diatoms and for manipulating silica biogenesis. This has opened the door for the production, through genetic engineering, of unique 3D nanomaterials with designed structures and functionalities.     

Factors influencing limit values for pine needle litter decomposition: a synthesis for boreal and temperate pine forest systems

We synthesized available data for decomposition of pine (Pinus) needle litter in pine forests to determine the litter chemical characteristics and climate factors that explained variation in the limit value, i.e. the level of accumulated mass loss at which the decomposition process either continues at a very low rate or possibly stops. Our data base included 56 separate studies on decomposition of pine needle litter, spanning Scots pine, lodgepole pine, Aleppo pine, stone pine and white pine, mainly incubated at the site of collection. Studies had 5 to 19 samplings, on average 10, and the decomposition was followed to a mass loss ranging from 47 to 83%, on average 67%. The periods from 3.0 to 5.4 years, on average 3.9 years, were of sufficient duration to allow estimates of limit values of decomposition. We used a linear mixed model with regression effects to relate limit values to potential explanatory variables, namely the sites’ long-term mean annual temperature (MAT) and mean annual precipitation (MAP) and to substrate-chemistry factors. Regarding the latter, we explored two models; one that included initial concentrations of water solubles, lignin, N, P, K, Ca, Mg, and Mn and one that included only lignin, N, Ca, and Mn to focus on those nutrients known to influence lignin degradation. Using backward elimination significant explanatory variables were determined. For litter decomposed in its site of origin we found the limit value to depend mainly on the initial concentration of Mn, with higher Mn concentrations resulting in higher accumulated mass loss. Thus, litter with higher Mn reached a higher limit value and left a smaller stable fraction. This is likely due to the fact that Mn is an essential component of ligninolytic enzymes important for degrading litter in the later stages of decomposition. Manganese has received little attention in decomposition studies to date. Given its significance in this synthesis, the role of Mn in influencing variation in the late stages of decomposition among ecosystems and among litters of other genera besides Pinus deserves further attention.     

Preferential action of rat brain cathepsin B as a peptidyl dipeptidase converting pro-opioid oligopeptides

Purified rat brain cathepsin B (EC 3.4.22.1) converted prodynorphins or proenkephalins to shorter active forms by the preferential removal of C-terminal dipeptides. The substrate affinities for Met-enkephalin-Arg-Phe or -Arg-Gly-Leu were Km 46 and 117 microM, and kcat/Km ratios were 67 and 115 microM-1, min-1, respectively. Met-Enkephalin was inactivated by the same mechanism (Km-450 microM; kcat/Km = 0.12 microM-1 min-1). The comparison of cathepsin B hydrolysis for pro-opioids, a synthetic hexapeptide and its fragments, C-blocked peptides (pro-opioid amides, Met-enkephalin amide, substance P), and bovine myelin basic protein, provided information on the influence of the C-terminal residues on dipeptide release, the rates as correlated to peptide length, and the optimal arrangement of residues favoring scission at the P1-P'1 sites. The brain enzyme was stereospecific and did not act on peptides with C-terminal D-amino acid substituents. Arg hindered and Pro blocked the release of C-terminal dipeptides when in the P'2 positions. The suppression of dipeptide release by agents inhibiting endopeptidase actions such as E-64 and leupeptin, and the endogenous brain factor (cerebrocystatin) point to similar catalytic mechanisms for the exopeptidase action.     

Formation of calyx-like contacts preferentially on appropriate target neurons in culture

The availability of culture systems for both Edinger Westphal and ciliary ganglion neurons has made it possible to examine the interactions in culture between two populations of vertebrate neurons that synapse in vivo. In the chick, Edinger Westphal neurons provide the sole presynaptic input to the ciliary ganglion and, through this projection, are responsible for the control of lens curvature (accommodation), iris constriction, and possibly smooth muscle function in the choroid layer of the eye. When embryonic chick Edinger Westphal and ciliary ganglion neurons were combined in culture and stained for enkephalin-like immunoreactivity to visualize Edinger Westphal terminals, stained calyx-like contacts were observed that resemble the calyciform terminals formed between Edinger Westphal processes and ciliary neurons in the ciliary ganglion in vivo. Although stained calyx-like contacts could also be found in Edinger Westphal-alone and ciliary ganglion-alone cultures, many more were observed when the two cell types were cultured together. The increase depended specifically on the ciliary ganglion neurons since substitution of either dorsal root ganglion or sympathetic ganglion neurons for them in the cocultures did not increase the number of calyx-like contacts staining positive for enkephalin over those present in cultures of Edinger Westphal neurons alone. When Edinger Westphal neurons were grown simultaneously with dorsal root and ciliary ganglion neurons, calyx-like contacts with enkephalin-like immunoreactivity were found to terminate preferentially on the latter. These findings suggest that vertebrate neurons can form morphologically specific contacts preferentially on appropriate target cells in culture in the absence of many of the potential cues present in the intact tissue.     

Effects of acorn masting on population dynamics of three forest-dwelling rodent species in Hokkaido,Japan

The effects of the abundance of acorns of the oak, Quercus crispula, on the population dynamics of three rodent species (Apodemus speciosus, A. argenteus, and Clethrionomys rufocanus) were analyzed using time series data (1992–2006). The data were obtained in a forest in northern Hokkaido, Japan, by live trapping rodents and directly counting acorns on the ground. Apodemus speciosus generally increased in abundance following acorn masting. However, the clear effect of acorn abundance was not detected for the other two rodent species. Acorns of Q. crispula contain tannins, which potentially have detrimental effects on herbivores. Apodemus speciosus may reduce the damage caused by acorn tannins with tannin-binding salivary proteins and tannase-producing bacteria, whereas such physiological tolerance to tannins is not known in the other two rodent species. The differences in the effects of acorns between the three species may be due to differences in their physiological tolerance to tannins.