Characterisation of the laccase-encoding gene abr2 of the dihydroxynaphthalene-like melanin gene cluster of Aspergillus fumigatus

Aspergillus fumigatus is an important pathogen of the immunocompromised host. Previously, it was shown that the polyketide synthase encoded by the pksP (alb1) gene represents a virulence determinant. pksP is part of a gene cluster involved in dihydroxynaphthalene (DHN)-like melanin biosynthesis. Because a putative laccase-encoding gene (abr2) is also part of the cluster and a laccase was found to represent a virulence factor in Cryptococcus neoformans, here, the Abr2 laccase was characterised. Deletion of the abr2 gene changed the gray-green conidial pigment to a brown color and the ornamentation of conidia was reduced compared with wild-type conidia. In contrast to the white pksP mutant, the susceptibility of the Δabr2 mutant against reactive oxygen species (ROS) was not increased, suggesting that the intermediate of DHN-like melanin produced up to the step catalysed by Abr2 already possesses ROS scavenging activity. In an intranasal mouse infection model, the Δabr2 mutant strain showed no reduction in virulence compared with the wild type. In the Δabr2 mutant, overall laccase activity was reduced only during sporulation, but not during vegetative growth. An abr2p-lacZ gene fusion was expressed during sporulation, but not during vegetative growth confirming the pattern of laccase activity due to Abr2.     

Dealing with Uncertainty in Spatially Explicit Population Models

It has been argued that spatially explicit population models (SEPMs) cannot provide reliable guidance for conservation biology because of the difficulty of obtaining direct estimates for their demographic and dispersal parameters and because of error propagation. We argue that appropriate model calibration procedures can access additional sources of information, compensating the lack of direct parameter estimates. Our objective is to show how model calibration using population-level data can facilitate the construction of SEPMs that produce reliable predictions for conservation even when direct parameter estimates are inadequate. We constructed a spatially explicit and individual-based population model for the dynamics of brown bears (Ursus arctos) after a reintroduction program in Austria. To calibrate the model we developed a procedure that compared the simulated population dynamics with distinct features of the known population dynamics (=patterns). This procedure detected model parameterizations that did not reproduce the known dynamics. Global sensitivity analysis of the uncalibrated model revealed high uncertainty in most model predictions due to large parameter uncertainties (coefficients of variation CV 0.8). However, the calibrated model yielded predictions with considerably reduced uncertainty (CV 0.2). A pattern or a combination of various patterns that embed information on the entire model dynamics can reduce the uncertainty in model predictions, and the application of different patterns with high information content yields the same model predictions. In contrast, a pattern that does not embed information on the entire population dynamics (e.g., bear observations taken from sub-areas of the study area) does not reduce uncertainty in model predictions. Because population-level data for defining (multiple) patterns are often available, our approach could be applied widely.     

Taxonomy of someDiploschistes spp. (lichenized ascomycetes,Thelotremataceae) containing gyrophoric acid

Three species which contain both gyrophoric and lecanoric acids and possess perithecioid ascomata are recognized in the genusDiploschistes. D. badius andD. gyrophoricus are described as new, whileD. subcupreus is reduced to synonymy withD. sticticus. Two species occur in the southern hemisphere, whileD. badius is found in N. America.     

Rhodobacteraceae on the marine brown alga Fucus spiralis are abundant and show physiological adaptation to an epiphytic lifestyle

Macroalgae harbour specific microbial communities on their surface that have functions related to host health and defence. In this study, the bacterial biofilm of the marine brown alga Fucus spiralis was investigated using 16S rRNA gene amplicon-based analysis and isolation of bacteria. Rhodobacteraceae (Alphaproteobacteria) were the predominant family constituting 23% of the epibacterial community. At the genus level, Sulfitobacter, Loktanella, Octadecabacter and a previously undescribed cluster were most abundant, and together they comprised 89% of the Rhodobacteraceae. Supported by a specific PCR approach, 23 different Rhodobacteraceae-affiliated strains were isolated from the surface of F. spiralis, which belonged to 12 established and three new genera. For seven strains, closely related sequences were detected in the 16S rRNA gene dataset. Growth experiments with substrates known to be produced by Fucus spp. showed that all of them were consumed by at least three strains, and vitamin B₁₂ was produced by 70% of the isolates. Since growth of F. spiralis depends on B₁₂ supplementation, bacteria may provide the alga with this vitamin. Most strains produced siderophores, which can enhance algal growth under iron-deficient conditions. Inhibiting properties against other bacteria were only observed when F. spiralis material was present in the medium. Thus, the physiological properties of the isolates indicated adaption to an epiphytic lifestyle.     

The HYP2 gene of Saccharomyces cerevisiae is essential for aerobic growth: characterization of different isoforms of the hypusine-containing protein Hyp2p and analysis of gene disruption mutants

In Saccharomyces cerevisiae, hypusine-containing proteins are encoded by two closely related genes, HYP1 and HYP2, which are regulated reciprocally by oxygen and heme. We have purified the aerobically expressed hypusine-containing proteins from yeast. The three proteins detected (two isoforms, which differ in their pI values, and a degradation product thereof, lacking the N-terminal 10 amino acid residues) are all encoded by HYP2. The N-terminus of both isoforms is formed by acetylation of a serine residue after cleavage of the first methionine. Cells mutant for hyp2 are unable to grow aerobically. However, under anaerobic conditions these mutants display no obvious phenotype, presumably because the strictly anaerobically expressed HYPI gene product (Hyp1p) is present. This implies that Hyp1p and Hyp2p fulfill very similar functions. In fact, Hyp1p can substitute for Hyp2p under aerobic conditions, when expressed under the control of the GAL1 promoter in hyp2 mutant cells.Abbreviations HYP1 and HYP2 S. cerevisiae genes encoding hypusine-containing protein Hyplp and Hyp2p, respectively     

A globin gene of ancient evolutionary origin in lower vertebrates: evidence for two distinct globin families in animals

Hemoglobin, myoglobin, neuroglobin, and cytoglobin are four types of vertebrate globins with distinct tissue distributions and functions. Here, we report the identification of a fifth and novel globin gene from fish and amphibians, which has apparently been lost in the evolution of higher vertebrates (Amniota). Because its function is presently unknown, we tentatively call it globin X (GbX). Globin X sequences were obtained from three fish species, the zebrafish Danio rerio, the goldfish Carassius auratus, and the pufferfish Tetraodon nigroviridis, and the clawed frog Silurana tropicalis. Globin X sequences are distinct from vertebrate hemoglobins, myoglobins, neuroglobins, and cytoglobins. Globin X displays the highest identity scores with neuroglobin (approximately 26% to 35%), although it is not a neuronal protein, as revealed by RT-PCR experiments on goldfish RNA from various tissues. The distal ligand-binding and the proximal heme-binding histidines (E7 and F8), as well as the conserved phenylalanine CD1 are present in the globin X sequences, but because of extensions at the N-terminal and C-terminal, the globin X proteins are longer than the typical eight alpha-helical globins and comprise about 200 amino acids. In addition to the conserved globin introns at helix positions B12.2 and G7.0, the globin X genes contain two introns in E10.2 and H10.0. The intron in E10.2 is shifted by 1 bp in respect to the vertebrate neuroglobin gene (E11.0), providing possible evidence for an intron sliding event. Phylogenetic analyses confirm an ancient evolutionary relationship of globin X with neuroglobin and suggest the existence of two distinct globin types in the last common ancestor of Protostomia and Deuterostomia.     

Mutations affecting somite formation in the Medaka (Oryzias latipes)

The metameric structure of the vertebrate trunk is generated by repeated formation of somites from the unsegmented presomitic mesoderm (PSM). We report the initial characterization of nine different mutants affecting segmentation that were isolated in a large-scale mutagenesis screen in Medaka (Oryzias latipes). Four mutants were identified that show a complete or partial absence of somites or somite boundaries. In addition, five mutations were found that cause fused somites or somites with irregular sizes and shapes. In situ hybridization analysis using specific markers involved in the segmentation clock and antero-posterior (A-P) polarity of somites revealed that the nine mutants can be compiled into two groups. In group 1, mutants exhibit defects in tailbud formation and PSM prepatterning, whereas A-P identity in the somites is defective in group 2 mutants. Three mutants (planlos, pll; schnelles ende, sne; samidare, sam) have characteristic phenotypes that are similar to those in zebrafish mutants affected in the Delta/Notch signaling pathway. The majority of mutants, however, exhibit somitic phenotypes distinct from those found in zebrafish, such as individually fused somites and irregular somite sizes. Thus, these Medaka mutants can be expected to provide clues to uncovering novel components essential for somitogenesis.