Grazing in a porous environment: 1. The effect of soil pore structure on C and N mineralization

The porous soil environment constrains grazing of microorganisms by microbivorous nematodes. In particular, at matric potentials at which water-filled pore spaces have capillary diameters less than nematode body diameters the effect of grazing, e.g. enhanced mineralization, should be reduced ('exclusion hypothesis') because nematodes cannot access their microbial forage. We examined C and N mineralization, microbial biomass C (by fumigation-extraction), the metabolic quotient (C mineralization per unit biomass C), nematode abundance, and soil water content in intact soil cores from an old field as a function of soil matric potential (−3 to −50 kPa). We expected, in accordance with the exclusion hypothesis, that nematode abundance, N and C mineralization would be reduced as matric potential decreased, i.e. as soils became drier. N mineralization was significantly greater than zero for −3 kPa but not for −10, −20 and −50 kPa. Microbial biomass C was less at −50 kPa than at −10 kPa, but not significantly different from biomass C at −3 and −20 kPa. The metabolic quotient was greatest at −50 kPa than any of the other matric potentials. From the exclusion hypothesis we expected significantly fewer nematodes to be present at −50 and −20 kPa representing water-filled capillary pore sizes less than 6 and 15 μm, respectively, than at −3 and −10 kPa. Microbivorous (fungivorous+bacterivorous) nematode abundance per unit mass of soil was not significantly different among matric potentials. Body diameters of nematodes ranged from 9 μm to 40 μm. We discuss several alternatives to the exclusion hypothesis, such as the 'enclosure hypothesis' which states that nematodes may become trapped in large water-filled pore spaces even when capillary pore diameters (as computed from matric potential) are smaller than body diameters. One of the expected outcomes of grazing in enclosures is the acceleration of nutrient cycling. This revised version was published online in June 2006 with corrections to the Cover Date.     

Xanthophyceaen assemblages during winter–spring flood: autecology and ecophysiology of Tribonema fonticolum and T. monochloron

The autecology and ecophysiology of two selected periphytic species of Xanthophyceae (Tribonema fonticolum and T. monochloron) were studied from seasonal pools of the inundation area, in the upper part of the Lužnice River (Třeboňsko Biosphere Reserve, Czech Republic) during winter–spring flood. Our studies have shown that these species differ in their ecological requirements (their temperature and light optima; inorganic carbon sources for photosynthesis; and also their ability to survive freezing and desiccation injuries). In our experiments, the optimal growth temperatures for both strains were higher than the temperatures of the water they were collected and isolated from. Tribonema monochloron has the rate of photosynthesis several times higher than T. fonticolum. In addition, the optimal growth temperatures were about 3–4°C lower for Tribonema monochloron than for T. fonticolum. From our results, we concluded that both strains of Tribonema prefer low intensities of irradiance. Both Tribonema strains were determined as CO₂ users, but we revealed the ability of T. fonticolum to use HCO₃⁻ in small amounts. In both Tribonema strains, 100% of the cells survived freezing down to −4°C. The cells’ viability after freezing at −40, −100 and −196°C was much higher for T. monochloron (about 40%) than for T. fonticolum (about 4%). With respect to desiccation damages, at temperatures of +4 and +20°C, T. monochloron (the species better adapted to low temperatures) did not survive. In contrast, about 80% cells of T. fonticolum survived desiccation at both temperatures. Handling editor: J. Padisak.     

Isolation and characterization of IgG1 with asymmetrical Fc glycosylation

N-glycosylation of immunoglobulin G (IgG) at asparigine residue 297 plays a critical role in antibody stability and immune cell-mediated Fc effector function. Current understanding pertaining to Fc glycosylation is based on studies with IgGs that are either fully glycosylated [both heavy chain (HC) glycosylated] or aglycosylated (neither HC glycosylated). No study has been reported on the properties of hemi-glycosylated IgGs, antibodies with asymmetrical glycosylation in the Fc region such that one HC is glycosylated and the other is aglycosylated. We report here for the first time a detailed study of how hemi-glycosylation affects the stability and functional activities of an IgG1 antibody, mAb-X, in comparison to its fully glycosylated counterpart. Our results show that hemi-glycosylation does not impact Fab-mediated antigen binding, nor does it impact neonatal Fc receptor binding. Hemi-glycosylated mAb-X has slightly decreased thermal stability in the CH2 domain and a moderate decrease (～20%) in C1q binding. More importantly, the hemi-glycosylated form shows significantly decreased binding affinities toward all Fc gamma receptors (FcγRs) including the high-affinity FcγRI, and the low-affinity FcγRIIA, FcγRIIB, FcγRIIIA and FcγRIIIB. The decreased binding affinities to FcγRs result in a 3.5-fold decrease in antibody-dependent cell cytotoxicity (ADCC). As ADCC often plays an important role in therapeutic antibody efficacy, glycosylation status will not only affect the antibody quality but also may impact the biological function of the product.     

Mapping of conformational IgE epitopes with peptide-specific monoclonal antibodies reveals simultaneous binding of different IgE antibodies to a surface patch on the major birch pollen allergen, Bet v 1

Allergic inflammation is based on the cross-linking of mast cell and basophil-bound IgE Abs and requires at least two binding sites for IgE on allergens, which are difficult to characterize because they are often conformational in nature. We studied the IgE recognition of birch pollen allergen Bet v 1, a major allergen for >100 million allergic patients. Monoclonal and polyclonal Abs raised against Bet v 1-derived peptides were used to compete with allergic patients' IgE binding to Bet v 1 to search for sequences involved in IgE recognition. Strong inhibitions of patients' IgE binding to Bet v 1 (52-75%) were obtained with mAbs specific for two peptides comprising aa 29-58 (P2) and aa 73-103 (P6) of Bet v 1. As determined by surface plasmon resonance, mAb2 specific for P2 and mAb12 specific for P6 showed high affinity, but only polyclonal rabbit anti-P2 and anti-P6 Abs or a combination of mAbs inhibited allergen-induced basophil degranulation. Thus, P2 and P6 define a surface patch on the Bet v 1 allergen, which allows simultaneous binding of several different IgE Abs required for efficient basophil and mast cell activation. This finding explains the high allergenic activity of the Bet v 1 allergen. The approach of using peptide-specific Abs for the mapping of conformational IgE epitopes on allergens may be generally applicable. It may allow discriminating highly allergenic from less allergenic allergen molecules and facilitate the rational design of active and passive allergen-specific immunotherapy strategies.     

Evaluation of texture features in spatial and frequency domain for automatic discrimination of histologic tissue

OBJECTIVE: To investigate the applicability of different texture features in automatic discrimination of microscopic views from benign common nevi and malignant melanoma lesions. STUDY DESIGN: In tissue counter analysis (TCA) the images are dissected into square elements used for feature calculation. The first class of features is based on the histogram, the co-occurrence matrix and the texture moments. The second class is derived from spectral properties of the wavelet Daubechie 4 and the Fourier transform. Square elements from images of a training set are classified by Classification and Regression Trees analysis. RESULTS: Features from the histogram and the co-occurrence matrix enable correct classification of 94.7% of nevi elements and 92.6% of melanoma elements in the training set. Classification results are applied to individual test set cases. Discriminant analysis based on the percentage of "malignant elements" showed correct classification of all nevi cases and 95% of melanoma cases. Features derived from the wavelet and Fourier spectrum showed correct results for 88.8% and 79.3% of nevi and 85.6% and 81.5% of melanoma elements, respectively. CONCLUSION: TCA is a potential diagnostic tool in automatic analysis of melanocytic skin tumors. Histogram and co-occurrence matrix features are superior to the wavelet and the Fourier features.     

Very-long-chain iso and anteiso branched fatty acids in N-acylphosphatidylethanolamines from a natural cyanobacterial mat of Calothrix sp.

A combination of TLC, ESI-MS/MS and GC-MS was used to identify unusual molecular species of N-acylphosphatidylethanolamines containing very-long-chain anteiso branched fatty acids (VLCFAs) from Calothrix sp. collected in Antarctica and determine their component VLCFA up to 33-methyltetratriacontanoic acid as picolinyl ester derivatives using GC-MS.     

Induction of metallothionein by exposure to normobaric 100% oxygen atmosphere in rats with different zinc supply

The objective of this study was to determine the effects of an oxygen enriched environment on the induction of the metalloprotein metallothionein (MT) and its relation to zinc metabolism in rats supplied with different levels of dietary zinc. Male albino rats were fed purified diets based on maize starch, egg white, saccharose and soybean oil differing in the concentration of zinc (1; 20; 100; 500 mg Zn/kg diet). At a dietary zinc supply of 1 mg/kg, the rats developed a zinc deficiency indicated by visual and biochemical parameters. At the end of the 37-day feeding period, half of the rats were exposed to 100% oxygen for 12 h.

The oxygen treatment significantly reduced plasma zinc in the zinc supplemented rats and reduced it in tendency in the zinc deficient rats. The MT concentration was increased in the zinc supplemented groups in the liver, kidney and lung. The oxygen treatment elevated the metallothionein concentration in the two high zinc supplemented groups (100 and 500 mg Zn/kg diet) in the liver. The response of the zinc concentration in plasma and of hepatic metallothionein levels to oxygen exposure indicates a role of metallothionein in zinc distribution or interactions with other trace elements to support antioxidant capacity, rather than an impact on direct scavenging activity of free radicals.     

FtsH-mediated repair of the photosystem II complex in response to light stress

A common feature of light stress in plants, algae, and cyanobacteria is the light-induced damage to the photosystem II complex (PSII), which catalyses the photosynthetic oxidation of water to molecular oxygen. A repair cycle operates to replace damaged subunits within PSII, in particular, the D1 reaction centre polypeptide, by newly synthesized copies. As yet the molecular details of this physiologically important process remain obscure. A key aspect of the process that has attracted much attention is the identity of the protease or proteases involved in D1 degradation. The results are summarized here of recent mutagenesis experiments that were designed to assess the functional importance of the DegP/HtrA and FtsH protease families in the cyanobacterium Synechocystis sp. PCC 6803. Based on these results and the analysis of Arabidopsis mutants, a general model for PSII repair is suggested in which FtsH complexes alone are able to degrade damaged D1.     

Costs and benefits of induced resistance in a clonal plant network

Plant defense theory suggests that inducible resistance has evolved to reduce the costs of constitutive defense expression. To assess the functional and potentially adaptive value of induced resistance it is necessary to quantify the costs and benefits associated with this plastic response. The ecological and evolutionary viability of induced defenses ultimately depends on the long-term balance between advantageous and disadvantageous consequences of defense induction. Stoloniferous plants can use their inter-ramet connections to share resources and signals and to systemically activate defense expression after local herbivory. This network-specific early-warning system may confer clonal plants with potentially high benefits. However, systemic defense induction can also be costly if local herbivory is not followed by a subsequent attack on connected ramets. We found significant costs and benefits of systemic induced resistance by comparing growth and performance of induced and control plants of the stoloniferous herb Trifolium repens in the presence and absence of herbivores.