Characterization of the major formamidopyrimidine–DNA glycosylase homolog in Mycobacterium tuberculosis and its linkage to variable tandem repeats

The ability to repair DNA damage is likely to play an important role in the survival of facultative intracellular parasites because they are exposed to high levels of reactive oxygen species and nitrogen intermediates inside phagocytes. Correcting oxidative damage in purines and pyrimidines is the primary function of the enzymes formamidopyrimidine (faPy)–DNA glycosylase (Fpg) and endonuclease VIII (Nei) of the base excision repair pathway, respectively. Four gene homologs, belonging to the fpg/nei family, have been identified in Mycobacterium tuberculosis H37Rv. The recombinant protein encoded by M. tuberculosis Rv2924c , termed Mtb-Fpg1, was overexpressed, purified and biochemically characterized. The enzyme removed faPy and 5-hydroxycytosine lesions, as well as 8-oxo-7,8-dihydroguanine (8oxoG) opposite to C, T and G. Mtb-Fpg1 thus exhibited substrate specificities typical for Fpg enzymes. Although Mtb-fpg1 showed nearly complete nucleotide sequence conservation in 32 M. tuberculosis isolates, the region upstream of Mtb-fpg1 in these strains contained tandem repeat motifs of variable length. A relationship between repeat length and Mtb-fpg1 expression level was demonstrated in M. tuberculosis strains, indicating that an increased length of the tandem repeats positively influenced the expression levels of Mtb-fpg1 . This is the first example of such a tandem repeat region of variable length being linked to the expression level of a bacterial gene.     

Persistent organic pollution in a high-Arctic top predator: sex-dependent thresholds in adult survival

In long-lived species, any negative effect of pollution on adult survival may pose serious hazards to breeding populations. In this study, we measured concentrations of various organochlorines (OCs) (polychlorinated biphenyl and OC pesticides) in the blood of a large number of adult glaucous gulls (Larus hyperboreus) breeding on Bjørnøya (Bear Island) in the Norwegian Arctic, and modelled their local survival using capture–recapture analysis. Survival was negatively associated with concentrations of OCs in the blood. The effect of OCs was nonlinear and evident only among birds with the highest concentrations (the uppermost deciles of contamination). The threshold for depressed survival differed between the sexes, with females being more sensitive to contamination. For birds with lower OC concentration, survival was very high, i.e. at the upper range of survival rates reported from glaucous and other large gull species in other, presumably less contaminated populations. We propose two non-exclusive explanations. First, at some threshold of OC concentration, parents (especially males) may abandon reproduction to maximize their own survival. Second, high contamination of OC may eliminate the most sensitive individuals from the population (especially among females), inducing a strong selection towards high-quality and less sensitive phenotypes.     

Aerobic microbial degradation of alginate in Laminaria hyperborea stipes containing different levels of polyphenols

The polyphenols present in brown seaweed tissue may seriously affect aerobic microbial degradation, particularly the alginate present. Laminaria hyperborea stipes, harvested at 59 °N off the Norwegian coast in autumn, were degraded at different levels of polyphenols in aerated batch reactors at 35 °C and pH 7. This was achieved by manipulating the relative amounts of peripheral tissue, by removing or adding the mechanically peeled outer phenolic layer, using standardized inocula already adapted to L. hyperborea degradation. The degradation of organic matter was clearly depressed by increasing the amount of peripheral tissue. Alginate lyase activity was also negatively correlated to the amount of peripheral tissue loaded, presumably due to the release of reactive polyphenols. The total digestion rates of alginate were reduced by more than a factor of two at enhanced amounts of peripheral tissue. The guluronic content of extracted Na-alginate increased during the degradation, despite the presence of significant amounts of guluronate specific alginate lyase activity. This revised version was published online in August 2006 with corrections to the Cover Date.     

Squamarina scopulorum (Lecanoraceae), a new lichen species from Norway

The new species Squamarina scopulorum Haugan & Timdal (sect. Petroplaca ) is described from Norway. It differs from the sympatric and morphologically closely similar species S. magnussonii and S. pachylepidea mainly in the color of the apothecial disc and in the thallus chemistry. The delimitation of the genus Squamarina and the family Squamarinaceae are briefly discussed.     

Acarospora intricata and A. wahlenbergii (Acarosporaceae) in Scandinavia

The taxonomy of the lichens Acarospora intricata and A. wahlenbergii is discussed, A. wahlenbergii is lectotypified, and the Scandinavian distribution of the two species is revised. The species differ in the type of paraphyses, the shape of the apothecia, and thallus chemistry. Two chemical strains of A. intricata , a psoromic acid strain and an acid deficient strain, are recorded. Psoromic acid is new to the Acarosporaceae.     

Tissue Distribution of 14C-Diflubenzuron in Atlantic Salmon (Salmo salar)

Diflubenzuron is a potent inhibitor of chitin synthesis, with potential use against salmon lice infestations. The absorption, distribution and elimination of the substance in Atlantic salmon was examined after a single, oral dose of 75 mg/kg body weight. The kinetic properties were studied by whole-body autoradiography, liquid scintillation counting and thin layer chromatography, using a 14C-labelled isotope of the substance. The drug was poorly absorbed from the intestine, but reached a concentration of more than 4 µg/g in the mucus layer of the skin 2 days after administration. If maintained for several days, this concentration is probably sufficient to control all moulting stages of sea lice in Atlantic salmon. The main route of excretion was via the bile.