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Bryophyte vegetation on volcanic rock outcrops and dead wood is studied in a near-natural montane beech stand in northern Hungary. Substrate specificity of the species and the existing interspecific relationships are described. The most important species combinations and their diversity are evaluated using information theoretical functions and Monte-Carlo simulations. All analyses are based on presence/absence data of 33 species in 1508 100 cm2 microplots. Most species exhibit strong substrate specificity. Of the species that occurred with frequencies higher than 10, 8 are associated to rock, 5 to dead wood and 5 to both substrate types. Analyses of interspecific associations and agglomerative classification reveal that frequent species of species-poor bare rocks are separated from species-rich assemblages of humus-rich outcrops and coarse woody debris. Monte Carlo simulations reveal that many species combinations are significantly more frequent than expected under the assumption of random combining of species. Observed number, diversity and evenness of species combinations are significantly lower, whereas interspecific constraint (expressed as associatum) is significantly higher than under the neutral models even when data are stratified according to substrate type. The presence of coarse woody debris, not only provides habitat for wood inhabiting bryophytes, but also results in diverse rupicolous bryophyte assemblages on humus-rich outcrops.
How are bryophyte alpha and beta diversities distributed across spatial scales along an elevational gradient in an oceanic island? Which mechanisms and drivers operate to shape them? Starting from a multiscale hierarchical sampling approach along an 1000 m elevational transect, we used additive diversity partitioning and null modeling to evaluate the contributions of the alpha and beta diversity components to overall bryophyte diversity in Terceira Island, Azores. Substrate-level diversity patterns were explored by means of the Sørensen Similarity Index and the Lloyd Index of Patchiness. Elevation-level beta diversity was decomposed into its replacement and richness differences components, with several environmental variables being evaluated as diversity predictors. Bryophyte diversity proved to be primarily due to beta diversity between elevation sites, followed by diversity among substrates. Compositional differences between neighboring sites decreased with elevation, being mainly caused by species replacement and correlating with differences in relative humidity and disturbance. At the substrate level, we found a great homogeneity in terms of species composition, coupled with a low substrate specialization rate. We conclude that, in Terceira’s native vegetation patches, regional processes, such as environmental gradients associated with elevation, play a greater role in shaping bryophyte diversity than local processes. Moister and less disturbed areas at mid-high elevation harbor a richer bryoflora, consistently more similar and stable between neighbouring sites. Simultaneously, the different substrates available are somewhat ecologically redundant, supporting few specialized species, pointing to these areas providing optimal habitat conditions for bryophytes. Our findings provide a better understanding of how bryophyte diversity is generated in Terceira Island, indicating that management and conservation measures should focus on island-level approaches, aiming to protect and rehabilitate additional natural vegetation patches at different elevations, especially in the severely disturbed lowlands.
involved in substrate specificity. Proc Natl Acad Sci USA 93, 3630–3635 (1996) Skurray RA Multidrug resistance proteins QacA and QacB from Staphylococcus aureus: membrane topology and
Under carbon starvation, Aspergillus nidulans produced a fungal/bacterial type chitinase, ChiB. The chiB gene was cloned and subcloned into pJC40 expression vector containing a 10XHis fusion tag, and the ChiB protein was expressed heterologously in Escherichia coli . Recombinant and native ChiB enzymes shared the same optimal pH ranges and showed similar substrate specificities with endo-acting cleavage patterns.
The present study was undertaken to establish a comparative account on hepatic mitochondrial oxygen consumption of Clarias gariepinus (fish), Bufo melanostictus (amphibian), Gallus gallus (bird) and Rattus norvegicus (mammal) and to correlate it with their specific metabolic rate (SMR). Mitochondrial oxygen consumption was measured with a Clarke-type electrode with succinate and pyruvate/malate as substrates. ADP was used to start state-III respiration. The results show that rats and chickens have higher oxygen consumption rate than that of fish and toads. Similarly, a species and substrate specific difference was also noticed in P/O (phosphate utilized per oxygen atom) ratio and respiratory control index. In case of rat, a significant negative correlation was noticed between P/O ratio and SMR with succinate as substrate. It is surmised that the observed difference in the mitochondrial respiration and P/O ratio in the above vertebrates is due to the difference in their metabolic activities.
Bacteria in a biofilm are enmeshed in a self-synthesized extracellular polysaccharide matrix (PGA), which is a linear polymer of β(1,6)-linked N-acetylglucosamine (GlcNAc) residues. Dispersin B (DspB), a soluble glycoside hydrolase produced by the periodontal pathogen Actinobacillus actinomycetemcomitans degrades PGA. The enzyme DspB is an α/β TIM-barrel protein and belongs to family 20 glycosyl hydrolases members. The enzyme activity of DspB with regard to its substrate specificity towards β(1,6)-linked GlcNAc polymers and its endo/exo character was investigated through ligand docking and the hydrolysis of synthetic oligosaccharides. Ligand docking analysis suggested that β(1,6)-linked GlcNAc oligosaccharide bound to the active site better that β(1,4)-linked GlcNAc oligosaccharide. Our combined results indicate that DspB is an exo-acting enzyme that hydrolyzes β(1,6)-linked N-acetylglucosamine oligomers.
Abstract
Continuous-flow methodologies have been applied to the synthesis of a number of fluorinated alkynyl arenes and heteroarenes. Through a series of optimizations reagent stoichiometry and reaction time were improved and substrate specificity was interrogated. Using optimized conditions under copper-free Sonogashira type couplings readily available arene building blocks were derivatized with fluoroalkynyl side chains in <10 min. Given the rapidity of the process and the enhanced purity profile of the products an immediate application of the work is in the development of 18F labeled versions of the agents for subsequent use in positron emission tomography (PET) imaging. A homolog of the Alzheimer's disease imaging agent Fallypride® was prepared using the methodology and additional analogs was identified.
A bacterium capable to grow on sulfanilic acid as sole carbon, nitrogen and sulfur source has been isolated. A unique feature of this strain is that it contains the full set of enzymes necessary for the biodegradation of sulfanilic acid. Taxonomical analysis identified our isolate as Sphingomonas subarctica SA1 sp. The biodegradation pathway of sulfanilic acid was investigated at the molecular level. Screening the substrate specificity of the strain disclosed its capacity to degrade six analogous aromatic compounds including p -aminobenzoic acid. Moreover, the strain was successfully used for removal of oil contaminations. S. subarctica SA1 seemed to use distinct enzyme cascades for decomposition of these molecules, since alternative enzymes were induced in cells grown on various substrates. However, the protein patterns appearing upon induction by sulfanilic acid and sulfocatechol were very similar to each other indicating common pathways for the degradation of these substrates. Cells grown on sulfanilic acid could convert p -aminobenzoic acid to some extent and vice versa. Two types of ring cleaving dioxygenases were detected in the cells grown on various substrates: one preferred protocatechol, while the other had higher activity with sulfocatechol. This latter enzyme, named as sulfocatechol dioxygenase was partially purified and characterized.
Eleven cold-tolerant Trichoderma isolates were screened for the production of proteolytic activities at 10 °C. Based on the activity profiles determined with paranitroanilide substrates at 5 °C, strain T221 identified as Trichoderma atroviride was selected for further investigations. The culture broth of the strain grown at 10 °C in casein-containing culture medium was concentrated by lyophilization and subjected to gel filtration, which was followed by chromatofocusing of the fraction showing the highest activity on N -benzoyl-Phe-Val-Arg-paranitroanilide. The purified enzyme had a molecular weight of 24 kDa, an isoelectric point of 7.3 and a pH optimum of 6.2. The temperature optimum of 25 °C and the low thermal stability suggested that it is a true cold-adapted enzyme. Substrate specificity data indicate that the enzyme is a proteinase with a preference for Arg or Lys at the P1 position. The effect of proteinase inhibitors suggests that the enzyme has a binding pocket similar to the one present in trypsin.
