Impact of simulated moose densities on abundance and richness of vegetation,herbivorous and predatory arthropods along a productivity gradient

Large herbivores can affect vegetation structure and species composition as well as material and energy flows in the ecosystem through their selective feeding, defecation, urination and trampling. These changes have a large potential to indirectly affect other trophic levels, but the mechanisms are poorly known. We studied the impacts of moose Alces alces browsing along a gradient of site productivity by experimentally simulating four different moose densities. Here we show that moose can affect the richness and abundance of three trophic levels in Swedish boreal forests through complex direct and indirect impacts, but in qualitatively different ways depending on how the physical habitat or food resources of a trophic level are affected. Vegetation richness had a hump‐shaped (unimodal) response to increased moose density. Leaf litter production decreased when browsing increased, which in turn depressed the abundance of flying prey for spiders. Consequently, spider abundance and richness declined monotonically. The responses of spider richness to moose density were further conditioned by site productivity: the response was positive at productive and negative at unproductive sites. In contrast, herbivorous Hemiptera were not affected by moose, most likely because the abundance of their food plants was not affected. The highest simulated moose density had an impact on all variables responding to moose even after a few years of treatment and can be considered as overabundance. We also show that the impacts of low or moderate moose density can be positive to some of the organisms negatively affected by high density. The level of herbivore population density that leads to substantial community impacts also depends on site factors, such as productivity.     

Conformational flexibility of a model protein upon immobilization on self-assembled monolayers

The present study reports on the retention of conformational flexibility of a model allosteric protein upon immobilization on self-assembled monolayers (SAMs) on gold. Organothiolated SAMs of different compositions were utilized for adsorptive and covalent attachment of bovine liver glutamate dehydrogenase (GDH), a well-characterized allosteric enzyme. Sensitive fluorimetric assays were developed to determine immobilization capacity, specific activity, and allosteric properties of the immobilized preparations as well as the potential for repeated use and continuous catalytic transformations. The allosteric response of the free and immobilized forms towards ADP, L-leucine and high concentrations of NAD(+), some of the well-known activators for this enzyme, were determined and compared. The enzyme immobilized by adsorption or chemical binding responded similarly to the activators with a greater degree of activation, as compared to the free form. Also loss of activity involving the two immobilization procedures were similar, suggesting that residues essential for catalytic activity or allosteric properties of GDH remained unchanged in the course of chemical modification. A recently established method was used to predict GDH orientation upon immobilization, which was found to explain some of the experimental results presented. The general significance of these observations in connection with retention of native properties of protein structures upon immobilization on SAMs is discussed.     

Detection of mutations in PCR products from clinical samples by surface plasmon resonance

Two different strategies for scanning and screening of mutations in polymerase chain reaction (PCR) products by hybridization analysis are described, employing real-time biospecific interaction analysis (BIA) for detection. Real-time BIA was used to detect differences in hybridization responses between PCR products and different 17-mer oligonucleotide probes. For the analysis using a biosensor instrument, two different experimental formats were investigated based on immobilization of either biotinylated PCR products or oligonucleotide probes onto a sensor chip. Applied on the human tumour suppressor p53 gene, differences in hybridization levels for full-match and mismatch situations employing both formats allowed the detection of point mutations in exon 6 PCR products, derived from a breast tumour biopsy sample. In addition, a mutant sample sequence could be detected in a 50/50 background of wild type exon 6 sequence. The suitability of the different formats for obtaining a regenerable system and a high throughput of samples is discussed. © 1997 John Wiley & Sons, Ltd.     

Purification and characterization of an early glycoprotein from adenovirus type 2-infected cells.

An adenovirus type 2 early glycoprotein with an apparent molecular weight of 19,000 (E19K) in sodium dodecyl sulfate-polyacrylamide gels has been extensively purified. Purification involved detergent solubilization of membrane fractions from infected cells, followed by affinity chromatography on a lectin column and DEAE-Sephadex chromatography. The purified material contained three polypeptides (E40K, E19K, E17.5K), with approximately 90% of the material in the E19K moiety. All three polypeptides yielded identical tryptic peptide maps. The E19K polypeptide contained glucosamine as revealed by [3H]glucosamine labeling of infected cells and amino acid analysis of the purified protein. Immunoprecipitation with a monospecific antiserum showed that the E19K polypeptide started to be synthesized at 2 h, with a maximal rate at 4 h after infection. It was also synthesized at a low rate late in the infectious cycle (12 to 24 h postinfection). Immunoprecipitation from three adenovirus type 2-transformed hamster embryo cell lines and two adenovirus type 2-transformed rat cell lines revealed that one of the hamster cell lines (ad2HE4) and one of the rat cell lines (A2T2C4) expressed this protein.     

Comparison of peptidase activities in some fungi pathogenic to arthropods

Peptidases, highly specific toward several synthetic chromogenic peptides, were found in the mycelia of four arthropod pathogenic fungi: Aphanomyces astaci, Beauveria bassiana, Metarrhizium anisopliae, and Paecilomyces farinosus. A. astaci peptidases had high hydrolyzing activities toward most of the peptides, especially those with arginine in the P1 position, while those of B. bassiana and P. farinosus readily hydrolyzed peptides with valine and arginine, as well as proline and tyrosine in the P2 and P1 positions, respectively. The hydrolyzing capacities of M. anisopliae peptidases were similar to A. astaci, but showed lower specific activities. Casein or azocoll was only hydrolyzed by A. astaci peptidases. B. bassiana and M. anisopliae had a very low hydrolyzing capacity toward casein and could not degrade azocoll. P. farinosus had no hydrolyzing activity toward casein or azocoll. Only peptidases from the crayfish pathogen A. astaci could degrade the crayfish cuticle. The peptidase preparations of A. astaci and B. bassiana hydrolyzing MeO-Suc-Arg-Pro-Tyr-pNA or Bz-Phe-Val-Arg-pNA were of the serine type. The possible importance of peptidase activity of arthropod pathogenic fungi in the infection process is discussed.     

ISMmy1, a novel insertion sequence of Mycoplasma mycoides subsp. mycoides small colony type

A new insertion sequence, ISMmy1, has been identified in the bovine pathogen Mycoplasma mycoides subsp. mycoides biotype small colony (MmymySC). The occurrence of ISMmy1 in 15 MmymySC strains and 12 other mycoplasmas was examined by Southern blotting. All MmymySC strains showed identical hybridisation patterns except for the type strain PG1(T), the vaccine strain T1Sr49, and the strain Afadé, which all had unique patterns. ISMmy1-like sequences were also found in the bovine pathogen Mycoplasma bovis strain Donetta(T) while mycoplasmas that are phylogenetically closer to MmymySC lack ISMmy1. This observation suggests horizontal transfer between MmymySC and M. bovis.     

A proteomics approach to investigate the process of Zn hyperaccumulation in Noccaea caerulescens (J & C. Presl) F.K. Meyer

Zinc (Zn) is an essential trace element in all living organisms, but is toxic in excess. Several plant species are able to accumulate Zn at extraordinarily high concentrations in the leaf epidermis without showing any toxicity symptoms. However, the molecular mechanisms of this phenomenon are still poorly understood. A state‐of‐the‐art quantitative 2D liquid chromatography/tandem mass spectrometry (2D‐LC‐MS/MS) proteomics approach was used to investigate the abundance of proteins involved in Zn hyperaccumulation in leaf epidermal and mesophyll tissues of Noccaea caerulescens. Furthermore, the Zn speciation in planta was analyzed by a size‐exclusion chromatography/inductively coupled plasma mass spectrometer (SEC‐ICP‐MS) method, in order to identify the Zn‐binding ligands and mechanisms responsible for Zn hyperaccumulation. Epidermal cells have an increased capability to cope with the oxidative stress that results from excess Zn, as indicated by a higher abundance of glutathione S‐transferase proteins. A Zn importer of the ZIP family was more abundant in the epidermal tissue than in the mesophyll tissue, but the vacuolar Zn transporter MTP1 was equally distributed. Almost all of the Zn located in the mesophyll was stored as Zn–nicotianamine complexes. In contrast, a much lower proportion of the Zn was found as Zn–nicotianamine complexes in the epidermis. However, these cells have higher concentrations of malate and citrate, and these organic acids are probably responsible for complexation of most epidermal Zn. Here we provide evidence for a cell type‐specific adaptation to excess Zn conditions and an increased ability to transport Zn into the epidermal vacuoles.