Tree diversity and species identity effects on soil fungi,protists and animals are context dependent

Plant species richness and the presence of certain influential species (sampling effect) drive the stability and functionality of ecosystems as well as primary production and biomass of consumers. However, little is known about these floristic effects on richness and community composition of soil biota in forest habitats owing to methodological constraints. We developed a DNA metabarcoding approach to identify the major eukaryote groups directly from soil with roughly species-level resolution. Using this method, we examined the effects of tree diversity and individual tree species on soil microbial biomass and taxonomic richness of soil biota in two experimental study systems in Finland and Estonia and accounted for edaphic variables and spatial autocorrelation. Our analyses revealed that the effects of tree diversity and individual species on soil biota are largely context dependent. Multiple regression and structural equation modelling suggested that biomass, soil pH, nutrients and tree species directly affect richness of different taxonomic groups. The community composition of most soil organisms was strongly correlated due to similar response to environmental predictors rather than causal relationships. On a local scale, soil resources and tree species have stronger effect on diversity of soil biota than tree species richness per se.     

Sequence and length recognition of the C-terminal turnover element of LpxC, a soluble substrate of the membrane-bound FtsH protease

The membrane-anchored FtsH protease is essential in Escherichia coli as it adjusts the cellular amount of LpxC, the key enzyme in lipopolysaccharide (LPS) biosynthesis. Both accumulation and depletion of LpxC are toxic to E. coli. By continuous proteolysis of LpxC, FtsH maintains a low concentration of LpxC and, hence, the proper equilibrium between LPS and phospholipids. The C terminus of LpxC is required for turnover. By adding this tail to glutathione-S-transferase (GST) we show that it is necessary but not sufficient for FtsH-mediated degradation. A detailed mutational analysis revealed six non-polar residues in the C terminus of LpxC that are critical for degradation. Alteration of the C-terminal AVLA motif towards the SsrA-like sequence ALAA directed LpxC to other cellular proteases reinforcing the importance of the C-terminal tail for targeting to FtsH. Short C-terminal truncations stabilized LpxC. Most mutations in the C terminus of LpxC left its enzymatic activity intact as was shown by growth assays, microscopy and 2-keto-3-deoxyoctonate (KDO) determination. The critical length of the turnover element was defined by internal deletions. A C-terminal tail of about 20 amino acids length is required for proteolysis of LpxC by FtsH.     

Crucial role of aspartic acid at position 265 in the CH2 domain for murine IgG2a and IgG2b Fc-associated effector functions

Replacement of aspartic acid by alanine at position 265 (D265A) in mouse IgG1 results in a complete loss of interaction between this isotype and low-affinity IgG Fc receptors (Fc gammaRIIB and Fc gammaRIII). However, it has not yet been defined whether the D265A substitution could exhibit similar effects on the interaction with two other Fc gammaR (Fc gammaRI and Fc gammaRIV) and on the activation of complement. To address this question, 34-3C anti-RBC IgG2a and IgG2b switch variants bearing the D265A mutation were generated, and their effector functions and in vivo pathogenicity were compared with those of the respective wild-type Abs. The introduction of the D265A mutation almost completely abolished the binding of 34-3C IgG2a and IgG2b to all four classes of Fc gammaR and the activation of complement. Consequently, these mutants were hardly pathogenic. Although oligosaccharide side chains of these mutants were found to contain higher levels of sialic acids than those of wild-type Abs, the analysis of enzymatically desialylated D265A variants ruled out the possibility that very poor Fc-associated effector functions of the D265A mutants were due to an increased level of the mutant Fc sialylation. Thus, our results demonstrate that aspartic acid at position 265 is a residue critically implicated in triggering the Fc-associated effector functions of IgG, probably by defining a crucial three-dimensional structure of the Fc region.     

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Ohne Zusammenfassung     

Probiotics enhance pancreatic glutathione biosynthesis and reduce oxidative stress in experimental acute pancreatitis

Factors determining severity of acute pancreatitis (AP) are poorly understood. Oxidative stress causes acinar cell injury and contributes to the severity, whereas prophylactic probiotics ameliorate experimental pancreatitis. Our objective was to study how probiotics affect oxidative stress, inflammation, and acinar cell injury during the early phase of AP. Fifty-three male Sprague-Dawley rats were randomly allocated into groups: 1) control, 2) sham procedure, 3) AP with no treatment, 4) AP with probiotics, and 5) AP with placebo. AP was induced under general anesthesia by intraductal glycodeoxycholate infusion (15 mM) and intravenous cerulein (5 microg.kg(-1).h(-1), for 6 h). Daily probiotics or placebo were administered intragastrically, starting 5 days prior to AP. After cerulein infusion, pancreas samples were collected for analysis including lipid peroxidation, glutathione, glutamate-cysteine-ligase activity, histological grading of pancreatic injury, and NF-kappaB activation. The severity of pancreatic injury correlated to oxidative damage (r = 0.9) and was ameliorated by probiotics (1.5 vs. placebo 5.5; P = 0.014). AP-induced NF-kappaB activation was reduced by probiotics (0.20 vs. placebo 0.53 OD(450nm)/mg nuclear protein; P < 0.001). Probiotics attenuated AP-induced lipid peroxidation (0.25 vs. placebo 0.51 pmol malondialdehyde/mg protein; P < 0.001). Not only was AP-induced glutathione depletion prevented (8.81 vs. placebo 4.1 micromol/mg protein, P < 0.001), probiotic pretreatment even increased glutathione compared with sham rats (8.81 vs. sham 6.18 miccromol/mg protein, P < 0.001). Biosynthesis of glutathione (glutamate-cysteine-ligase activity) was enhanced in probiotic-pretreated animals. Probiotics enhanced the biosynthesis of glutathione, which may have reduced activation of inflammation and acinar cell injury and ameliorated experimental AP, via a reduction in oxidative stress.     

Specificity and function of monoclonal antibodies directed against Ewing sarcoma cells

A selection of 16 monoclonal antibodies has been produced against a fresh Ewing's sarcoma (ES) tumor mixed with a permanent ES cell line. The majority of antibodies identify an 80-kDa molecule, which is not detected on healthy tissues except on certain cultured monocytes. One antibody recognize the CD2 ligand MIC2 and 2 antibodies (numbers 13 and 16) define a higher-molecular-mass antigen. Antibody 16 is also expressed on mesenchymal fibroblasts of bone marrow or fetal origin. Tumorspecific antigen expression is potentially linked to the chromosome 22 abnormality decribed in Ewing's sarcoma.     

Vertical profiles of CH4 concentrations,dissolved substrates and processes involved in CH4 production in a flooded Italian rice field

Vertical profiles were measured in soil cores taken from flooded rice fields in the Po valley during July and August 1990. Methane concentrations generally increased with depth and reached maximum values of 150–500 μM in 5–13 cm depth. However, the shape of the profiles was very different when studying different soil cores. The CH₄ content of gas bubbles showed a similar variability which apparently was due to spatial rather than temporal inhomogeneities. Similar inhomogeneities were observed in the vertical profiles of acetate, propionate, lactate, and formate which showed maximum values of 1500, 66, 135, and 153, μM, respectively. However, maxima and minima of the vertical profiles of the different substates usually coincided in one particular soil core. Large inhomogeneities in the vertical profiles were also observed for the rates of total CH₄ production, however, the percentage contribution of H₂/CO₂ to CH₄ production was relatively homogeneous at 24 ± 7% (SD). Similarly, the H₂ content of gas bubbles was relatively constant at 93.3 ± 9.6 ppmv when randomly sampled in the rice field at different times of the day. A small contribution (6%) of H₂/CO₂ to acetate production was also observed. Vertical profiles of the respiratory index (RI) for [2-¹⁴C] acetate showed that acetate was predominantly degraded by methanogenesis in 5–11 cm depth, but by respiration in the surface soil (3 cm depth) and in soil layers below 13–16 cm depth which coincided with a transition of the colour (grey to reddish) and the physical characteristics (porosity, density) of the soil. The observations indicate that the microbial community which degrades organic matter to CH₄ is in itself relatively homogenous, but operates at highly variable rates within the soil structure. Author for correspondence