Blood reactions in vitro in crayfish against a fungal parasite, Aphanomyces astaci

The immediate and subsequent reactions in crayfish blood upon making contact with hyphae of the crayfish plague fungus were observed in vitro. Blood cells agglomerated and clumped rapidly on the hyphae in streaming blood. Very brief contact by chance with a hypha, or with cell extensions from cells or a cell clump on the hypha, caused flowing cells to stop and adhere. Chemotaxis was not believed to be of any importance. Particles originating from hemocyte granules were specifically attached to, and “encapsulated” the distal portion of, the hypha (even without the presence of the cells themselves), where their content of polyphenol oxidase became activated. These processes may be connected with the defense mechanism in crayfish. Within a few hours the process of melanization could be observed on the hyphal surface. Both the enzyme(s) and the substrate(s) for the melanization reaction seem to originate from the blood cells. Dihydroxyphenylalanine (DOPA) could replace the natural substrate and greatly enhanced the process. The melanization in whole blood was much heavier in a crayfish resistant to the disease than in a susceptible one.     

Sea trout as a carrier of infectious salmon anaemia virus

Sea trout did not develop symptoms or gross clinical signs of infectious salmon anaemia (ISA) when injected with ascites from salmon, but ISA virus was propagated and haematocrit values dropped. The virus was transmitted from trout to salmon.     

Balancing selection,sexual selection and geographic structure in MHC genes of Great Snipe

Signatures of balancing selection are often found when investigating the extremely polymorphic regions of major histocompatibility complex (MHC) genes, and it is generally accepted that selective forces maintain this polymorphism. However, the exact nature of the selection is controversial. Theoretical studies have mainly focused on overdominance and/or frequency dependent selection while laboratory studies have emphasised the role of mate choice. Empirical field data, on the other hand, have been relatively scarce. Previously we have found that geographic structure in MHC class II genes of the Great Snipe (Gallinago media) is too pronounced to be explained by neutral forces alone. Here we test the hypothesis that sexual selection on MHC alleles may be influencing this geographic structure between mountain and lowland populations. We found evidence of balancing selection acting on MHC genes in the form of a higher rate of amino-acid changing substitutions compared to silent substitutions in the peptide binding regions. Not only natural selection but also sexual selection may influence MHC polymorphism in this bird because certain MHC alleles have been found to be associated with higher male mating success. Contrary to predictions from negative frequency dependent selection, males carrying locally rare alleles did not have a mating advantage. Instead, the mating success of alleles in a mountain population was positively correlated to their relative frequency in the mountains compared to the lowlands, implying that locally adapted MHC alleles may also be favoured by sexual selection.     

Virus-like particles associated with heart and skeletal muscle inflammation (HSMI)

The first cases of heart and skeletal muscle inflammation (HSMI), in Atlantic salmon Salmo salar were registered in 1999 in the Hitra/Fr?ya area of Norway. The disease has since spread south to Rogaland, i.e. the southernmost county with salmon farming in Norway. The disease outbreaks usually start 5 to 9 mo after release into seawater but may occur as early as 2 wk after sea release. The present study focuses on possible pathogens associated with HSMI. It was not possible to find any parasites or bacteria that could explain HSMI, and none of the well-known viruses (infectious salmon anaemia virus, Norwegian salmonid alphavirus, infectious pancreatic necrosis virus, Atlantic salmonid paramyxovirus) were consistently present. Use of transmission electron microscopy showed the presence of epitheliocystis agent in 3 of 4 farms included in this study, and several virus-like particles. Type I and Type II virus particles, previously described for salmon suffering from haemorrhagic smolt syndrome (HSS), and erythrocytic inclusion body syndrome (EIBS) virus were consistently present in salmon suffering from HSMI in all 4 farms included in this study. The 2 HSS viruses (Type I and Type II) were also cultured in Atlantic salmon kidney (ASK) cells from salmon suffering from HSMI. However, a causal relationship between the observed virus particles and HSMI remains to be demonstrated.     

Measuring Fine Root Turnover in Forest Ecosystems

Development of direct and indirect methods for measuring root turnover and the status of knowledge on fine root turnover in forest ecosystems are discussed. While soil and ingrowth cores give estimates of standing root biomass and relative growth, respectively, minirhizotrons provide estimates of median root longevity (turnover time) i.e., the time by which 50% of the roots are dead. Advanced minirhizotron and carbon tracer studies combined with demographic statistical methods and new models hold the promise of improving our fundamental understanding of the factors controlling root turnover. Using minirhizotron data, fine root turnover (y⁻¹) can be estimated in two ways: as the ratio of annual root length production to average live root length observed and as the inverse of median root longevity. Fine root production and mortality can be estimated by combining data from minirhizotrons and soil cores, provided that these data are based on roots of the same diameter class (e.g., < 1 mm in diameter) and changes in the same time steps. Fluxes of carbon and nutrients via fine root mortality can then be estimated by multiplying the amount of carbon and nutrients in fine root biomass by fine root turnover. It is suggested that the minirhizotron method is suitable for estimating median fine root longevity. In comparison to the minirhizotron method, the radio carbon technique favor larger fine roots that are less dynamics. We need to reconcile and improve both methods to develop a more complete understanding of root turnover.     

Francisella sp. (Family Francisellaceae) causing mortality in Norwegian cod (Gadus morhua) farming

In 2004, a new disease was detected in cod (Gadus morhua) in western Norway. Affected cod had white granulomas in the visceral organs and skin. A species of Francisella was isolated on blood agar plates from moribund cod. The bacterium could be grown at temperatures ranging from 6 to 22°C, but did not grow at 37°C. Challenge experiments showed that Francisella sp. was the cause for the new disease. The 16S rDNA gene sequence from Francisella sp. showed 99.17% similarity to F. philomiragia, and the 16S–23S ribosomal RNA intergenic spacer (249 nt), shows a similarity with that from Francisella isolated from tilapia and F. tularensis of 96.8 and 35.9%, respectively. The 23S sequence is more similar to F. tularensis, 97.7% (2,862 nt), compared to the tilapia isolate 96.8% (2,131 nt). The partial putative outer membrane protein (FopA) sequence (781 nt) from Francisella sp. shows a similarity with that from F. tularensis and F. philomiragia of 77.3 and 98.2%, respectively. Based on sequence data, culturing temperatures and pathogenicity for cod, it is suggested that this Francisella sp. from cod could be a new species of Francisella, Family Francisellaceae.     

Kinetics and mechanisms of depolymerization of alginate and chitosan in aqueous solution

The kinetics and mechanisms of depolymerization of aqueous chitosan and alginate solutions at elevated temperatures have been investigated. Chitosan salts of different degree of acetylation (F_A), type of counterions (-glutamate, -chloride) and degree of purity were studied. One commercially available highly purified sodium alginate sample with high content of guluronic acid (G) was also studied. Furthermore, the influence of oxygen, H⁺ and OH⁻ ions on the initial depolymerization rates was investigated. Depolymerization kinetics was followed by measuring the time courses of the apparent viscosity and the intrinsic viscosity. The initial rate constants for depolymerization were determined from the intrinsic viscosity data converted to a quantity proportional to the fraction of bonds broken. The activation energies of the chitosan chloride and chitosan glutamate solutions with pH close to 5 and the same degree of acetylation, F_A = 0.14, were determined from the initial rate constants to be 76 ± 13 kJ/mol and 80 ± 11 kJ/mol, respectively.The results reported herein suggest that the stability of aqueous chitosan and alginate solutions at pH values 5–8 will be influenced by oxidative–reductive depolymerization (ORD) as the primary mechanism as long as transition metal ions are presented in the samples. Acid – and alkaline depolymerization will be the primary mechanisms for highly purified samples.