Immobilized Growth of the Peridinin-Producing Marine Dinoflagellate Symbiodinium in a Simple Biofilm Photobioreactor

Products from phototrophic dinoflagellates such as toxins or pigments are potentially important for applications in the biomedical sciences, especially in drug development. However, the technical cultivation of these organisms is often problematic due to their sensitivity to hydrodynamic (shear) stress that is a characteristic of suspension-based closed photobioreactors (PBRs). It is thus often thought that most species of dinoflagellates are non-cultivable at a technical scale. Recent advances in the development of biofilm PBRs that rely on immobilization of microalgae may hold potential to circumvent this major technical problem in dinoflagellate cultivation. In the present study, the dinoflagellate Symbiodinium voratum was grown immobilized on a Twin-Layer PBR for isolation of the carotenoid peridinin, an anti-cancerogenic compound. Biomass productivities ranged from 1.0 to 11.0 g m^?2 day^?1 dry matter per vertical growth surface and a maximal biomass yield of 114.5 g m^?2, depending on light intensity, supplementary CO₂, and type of substrate (paper or polycarbonate membrane) used. Compared to a suspension culture, the performance of the Twin-Layer PBRs exhibited significantly higher growth rates and maximal biomass yield. In the Twin-Layer PBR a maximal peridinin productivity of 24 mg m^?2 day^?1 was determined at a light intensity of 74 μmol m^?2 s^?1, although the highest peridinin content per dry weight (1.7 % w/w) was attained at lower light intensities. The results demonstrate that a biofilm-based PBR that minimizes hydrodynamic shear forces is applicable to technical-scale cultivation of dinoflagellates and may foster biotechnological applications of these abundant marine protists.     

Host Genotype Shapes the Foliar Fungal Microbiome of Balsam Poplar (Populus balsamifera)

Foliar fungal communities of plants are diverse and ubiquitous. In grasses endophytes may increase host fitness; in trees, their ecological roles are poorly understood. We investigated whether the genotype of the host tree influences community structure of foliar fungi. We sampled leaves from genotyped balsam poplars from across the species'' range, and applied 454 amplicon sequencing to characterize foliar fungal communities. At the time of the sampling the poplars had been growing in a common garden for two years. We found diverse fungal communities associated with the poplar leaves. Linear discriminant analysis and generalized linear models showed that host genotypes had a structuring effect on the composition of foliar fungal communities. The observed patterns may be explained by a filtering mechanism which allows the trees to selectively recruit fungal strains from the environment. Alternatively, host genotype-specific fungal communities may be present in the tree systemically, and persist in the host even after two clonal reproductions. Both scenarios are consistent with host tree adaptation to specific foliar fungal communities and suggest that there is a functional basis for the strong biotic interaction.     

Evolutionary Paths of the cAMP-Dependent Protein Kinase (PKA) Catalytic Subunits

3′,5′-cyclic adenosine monophosphate (cAMP) dependent protein kinase or protein kinase A (PKA) has served as a prototype for the large family of protein kinases that are crucially important for signal transduction in eukaryotic cells. The PKA catalytic subunits Cα and Cβ, encoded by the two genes PRKACA and PRKACB, respectively, are among the best understood and characterized human kinases. Here we have studied the evolution of this gene family in chordates, arthropods, mollusks and other animals employing probabilistic methods and show that Cα and Cβ arose by duplication of an ancestral PKA catalytic subunit in a common ancestor of vertebrates. The two genes have subsequently been duplicated in teleost fishes. The evolution of the PRKACG retroposon in simians was also investigated. Although the degree of sequence conservation in the PKA Cα/Cβ kinase family is exceptionally high, a small set of signature residues defining Cα and Cβ subfamilies were identified. These conserved residues might be important for functions that are unique to the Cα or Cβ clades. This study also provides a good example of a seemingly simple phylogenetic problem which, due to a very high degree of sequence conservation and corresponding weak phylogenetic signals, combined with problematic nonphylogenetic signals, is nontrivial for state-of-the-art probabilistic phylogenetic methods.     

Seasonality of harpacticoids (Crustacea, Copepoda) in a tidal pool in subarctic south-western Iceland

Seasonality of phytal harpacticoids was studied in a tidal pool in the lower rocky intertidal in south-western Iceland. Samples of the red alga Chondrus crispus were taken monthly from January 1999 to January 2000. Multidimensional scaling ordination showed a clear seasonal pattern in phytal species composition and abundance of individual species. Of more than 70 species recorded, Zaus spinatus accounted for one third of the total abundance. Many species were found only sporadically and analysis of the data was confined primarily to the eleven most common species (Zaus spinatus, Ectinosomaspp., Tisbespp., Ameira longipes, Mesochra sp. 2 and Mesochrasp. 1, Dactylopusia vulgaris, Amphiascoides debilis, Amphiascussp. 1, Parastenhelia spinosa and Amphiascus minutus). Four showed no significant variation in total abundance through the year, while the remainder had more or less pronounced peaks in summer. Most species (on which data was sufficient) had a prolonged (≥ 6 months) to a continuous breeding season, as indicated by the presence of ovigerous females. This contrasts with most shallow-water temperate and subarctic invertebrates which appear to have more restricted breeding seasons. Our results extend to higher latitudes the general conclusion that many temperate phytal harpacticoids have a long, often continuous, breeding season. The reasons for this are unclear but, presumably, involve access to continuous food supply. There is strong evidence that variations in abundance of several species in the tidal pool were not due only to recruitment, but also to migration to the pool in summer and emigration in autumn.     

Human Adaptive Behavior in Common Pool Resource Systems

Overexploitation of common-pool resources, resulting from uncooperative harvest behavior, is a major problem in many social-ecological systems. Feedbacks between user behavior and resource productivity induce non-linear dynamics in the harvest and the resource stock that complicate the understanding and the prediction of the co-evolutionary system. With an adaptive model constrained by data from a behavioral economic experiment, we show that users’ expectations of future pay-offs vary as a result of the previous harvest experience, the time-horizon, and the ability to communicate. In our model, harvest behavior is a trait that adjusts to continuously changing potential returns according to a trade-off between the users’ current harvest and the discounted future productivity of the resource. Given a maximum discount factor, which quantifies the users’ perception of future pay-offs, the temporal dynamics of harvest behavior and ecological resource can be predicted. Our results reveal a non-linear relation between the previous harvest and current discount rates, which is most sensitive around a reference harvest level. While higher than expected returns resulting from cooperative harvesting in the past increase the importance of future resource productivity and foster sustainability, harvests below the reference level lead to a downward spiral of increasing overexploitation and disappointing returns.     

Climate and climatic variability at Lake Myvatn

The climate of the Lake Myvatn region is examined through the use of weather station data, using the years from 1971 to 2000 as a reference period. Variations in mean monthly temperature and precipitation at Reykjahlid (Myvatn) are compared with variations at seven other weather stations in north east Iceland. The area is drier and colder than coastal stations and exhibits a seasonal cycle in temperature that is larger than found at the coast. The temperature is significantly influenced by the number of sunlight hours only during the summer months. During summer, the influence of a sea breeze circulation can be clearly identified.The variability of climate since 1936 is also examined in comparison with the seven other weather stations. It is found that temperature variations at the different stations are highly correlated, but for precipitation the correlation is significant but much weaker.The influence of the large scale atmospheric circulation on temperature and precipitation at Lake Myvatn is also examined. It is found that the air temperature at Lake Myvatn is most sensitive to an east-west dipole in the large scale sea surface pressure field, i.e. to a pattern that is very different from the spatial pattern associated with the North Atlantic Oscillation (NAO). Precipitation at Lake Myvatn is to some degree influenced by the NAO, but generally precipitation is associated with northerly winds and cold temperatures whereas southerly winds at Lake Myvatn are likely to be drier.     

Insertion specificity and trans -activation of IS801

The transposable element IS801, isolated from plasmid pMMC7105 of Pseudomonas syringae pv. phaseolicola, transposes in Escherichia coli to plasmid targets, expressing a relatively relaxed target specificity. The target sequences are tetramers with homology with the left terminus (GAAC) of the transposing unit, the alternative targets being GAAC, GGAC, CAAG, and CGAC. In the areas flanking IS801 in 13 different locations, no similarities other than the target tetramer were observed. The transposase is physically and functionally separable from the transposing unit since transposition of constructs carrying marker genes occurs with the transposase expressed in trans. The IS801 transposase shows amino acid sequence homology to the transposases of the E. coli elements IS91 and IS1294. These tranposases contain conserved amino acid motifs found in the replicases of certain plasmids that replicate as rolling circles. Received: 18 March 1998 / Accepted: 15 August 1998