Seasonal growth potential of rare lake water bacteria suggest their disproportional contribution to carbon fluxes

We studied the seasonal growth potential of opportunistic bacterial populations in Lake Zurich (Switzerland) by a series of grazer‐free dilution culture assays. Pronounced shifts in the composition of the bacterial assemblages were observed within one doubling of total cell numbers, from initially abundant Actinobacteria to other fast‐growing microbial lineages. Small populations with growth potentials far above community average were detected throughout the year with striking seasonal differences in their respective taxonomic affiliations. Members of Cytophaga‐Flavobacteria (CF) were disproportionally proliferating only during phytoplankton blooms in spring and summer, while Beta‐ and Gammaproteobacteria showed superior growth at all other occasions. Growth rates of Alphaproteobacteria and esp. Sphingomonadaceae were significantly correlated to water temperatures and were far above community average in summer. Within the genus Flavobacterium, two species‐like populations showed a tendency for fast growth in most experiments, while four others were exclusively proliferating either during a spring or during a summer phytoplankton bloom. Their high growth potentials but low in situ abundances hint at a tight control by bacterivorous grazers and at a consequently accelerated carbon flux to higher trophic levels.     

Identification of a new membrane-permeable inhibitor against inositol-1,4,5-trisphosphate-3-kinase A

Ectopic expression of the neuron-specific inositol-1,4,5-trisphosphate-3-kinase A (ITPKA) in lung cancer cells increases their metastatic potential because the protein exhibits two actin regulating activities; it bundles actin filaments and regulates inositol-1,4,5-trisphosphate (InsP₃)-mediated calcium signals by phosphorylating InsP₃. Thus, in order to inhibit the metastasis-promoting activity of ITPKA, both its actin bundling and its InsP₃kinase activity has to be blocked. In this study, we performed a high throughput screen in order to identify specific and membrane-permeable substances against the InsP₃kinase activity. Among 341,44 small molecules, 237 compounds (0.7%) were identified as potential InsP₃kinase inhibitors. After determination of IC₅₀-values, the three compounds with highest specificity and highest hydrophobicity (EPPC-3, BAMB-4, MEPTT-3) were further characterized. Only BAMB-4 was nearly completely taken up by H1299 cells and remained stable after cellular uptake, thus exhibiting a robust stability and a high membrane permeability. Determination of the inhibitor type revealed that BAMB-4 belongs to the group of mixed type inhibitors. Taken together, for the first time we identified a highly membrane-permeable inhibitor against the InsP₃kinase activity of ITPKA providing the possibility to partly inhibit the metastasis-promoting effect of ITPKA in lung tumor cells.     

Ultrastruktur und Jodaufnahme der Schilddrüse bei Larven des Krallenfrosches (Xenopus laevis Daud.)

Zusammenfassung Ziel dieser Untersuchung war eine physiologische Deutung der Ultrastruktur von Schilddrüsenepithelzellen bei Larven von Xenopus laevis. Dazu wurden elektronenmikroskopische Bilder mit morphometrischen Methoden quantitativ ausgewertet und die Ergebnisse mit Jodaufnahmedaten verglichen. So konnte die Aktivierung der Schilddrüse durch TSH bei kälteblockierten bzw. hypophysektomierten Tieren mit Veränderungen während der spontanen Metamorphose verglichen werden.Ihrer Ultrastruktur nach sind die Schilddrüsen blockierter Prometamorphoselarven in der Entwicklung auf ein früheres Stadium zurückversetzt. Auch zeigen hypophysektomierte Larven keine spontane Jodaufnahme. Eine einmalige TSH-Injektion läßt dann die Größe und Form der verschiedenen Organellen vorübergehend den Zustand der Kontrollen erreichen. Besonders rasch und stark sprechen einerseits die Kernstruktur, andererseits Mikrovilli und Kolloidtropfenvolumen, welche die Resorption von Thyreoglobulin charakterisieren, auf den TSH-Reiz an. Die Jodaufnahme verläuft langsamer. Auch reagieren die an der Synthese beteiligten Organellen später und schwächer.In der spontanen Metamorphose wachsen die Schilddrüsen, nach Totalvolumen, Cytoplasmavolumen einzelner Zellen und Epithelhöhe beurteilt, bis zum Ende der Metamorphose weiter und nehmen entsprechend mehr Jod auf. Ebenso wird während der ganzen Klimax die Kolloidresorption der einzelnen Zellen stärker. Aus den Ergebnissen wird geschlossen, daß die TSH-Sekretion schon in der Prometamorphose einsetzt und bis gegen Ende der Metamorphose zunimmt.

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Ultrastructure and iodine uptake of the thyroid gland in larvae of Xenopus laevis daud

Summary The epithelial cells of the thyroid gland in larvae of Xenopus laevis were investigated with the electron microscope. Morphometrical methods yielded quantitative data on the morphology. The uptake of radioactive iodine was studied in order to obtain information on the physiological activity. Thus changes in the thyroid gland following the injection of TSH in tadpoles which had been hypophysectomized or blocked at low temperature were compared with the development of glands during spontaneous metamorphosis.The thyroid glands of blocked prometamorphic larvae resemble those of younger developmental stages as judged by their ultrastructure. In addition no spontaneous accumulation of iodine is observed. Following an injection of TSH the morphology of the various organelles becomes temporarily identical to that of the controls. These changes are most prominent in the nucleus as well as in the microvilli and the colloid droplets, which characterize the resorption of thyroglobulin. Only a minor effect of the TSH stimulus is found on iodine uptake and on organelles concerned with protein synthesis.During normal metamorphosis an increase is observed in the following parameters: (1) volume of the thyroid gland, (2) volume of the cytoplasm and height of single epithelial cells, (3) resorption of colloid, (4) iodine uptake. This increase persists until the end of the climax. Based on the present results TSH secretion is assumed to start in early prometamorphosis and to rise up to the end of metamorphosis.

Herrn Prof. Dr. R. Weber möchte ich für seine Hilfe bestens danken.     

Wheat alleles introgress into selfing wild relatives: empirical estimates from approximate Bayesian computation in Aegilops triuncialis

Extensive gene flow between wheat (Triticum sp.) and several wild relatives of the genus Aegilops has recently been detected despite notoriously high levels of selfing in these species. Here, we assess and model the spread of wheat alleles into natural populations of the barbed goatgrass (Aegilops triuncialis), a wild wheat relative prevailing in the Mediterranean flora. Our sampling, based on an extensive survey of 31 Ae. triuncialis populations collected along a 60 km × 20 km area in southern Spain (Grazalema Mountain chain, Andalousia, totalling 458 specimens), is completed with 33 wheat cultivars representative of the European domesticated pool. All specimens were genotyped with amplified fragment length polymorphism with the aim of estimating wheat admixture levels in Ae. triuncialis populations. This survey first confirmed extensive hybridization and backcrossing of wheat into the wild species. We then used explicit modelling of populations and approximate Bayesian computation to estimate the selfing rate of Ae. triuncialis along with the magnitude, the tempo and the geographical distance over which wheat alleles introgress into Ae. triuncialis populations. These simulations confirmed that extensive introgression of wheat alleles (2.7 × 10^?4 wheat immigrants for each Ae. triuncialis resident, at each generation) into Ae. triuncialis occurs despite a high selfing rate (Fis ≈ 1 and selfing rate = 97%). These results are discussed in the light of risks associated with the release of genetically modified wheat cultivars in Mediterranean agrosystems.     

Suppression and Restoration of Lesion Formation in Arabidopsis lsd Mutants

Systemic acquired resistance (SAR) is a broad-spectrum, systemic defense response that is activated in many plant species after pathogen infection. We have previously described Arabidopsis mutants that constitutively express SAR and concomitantly develop lesions simulating disease (lsd). Here, we describe two new mutants, lsd6 and lsd7, that develop spontaneous necrotic lesions and possess elevated levels of salicylic acid (SA) as well as heightened disease resistance, similar to the previously characterized lsd and accelerated cell death (acd2) mutants. Genetic analysis of lsd6 and lsd7 showed that the mutant phenotypes segregated as simple dominant traits. When crossed with transgenic Arabidopsis plants containing the SA-degrading enzyme salicylate hydroxylase, the F1 progeny showed suppression of both SAR gene expression and resistance. In addition, salicylate hydroxylase suppressed lesion formation in the F1 progeny, suggesting that SA or some SA-dependent process may have a role in pathogen-associated cell death. Surprisingly, lesions were restored in the lsd6 F1 progeny after the application of either 2,6-dichloroisonicotinic acid or SA. Lesions were not restored by treatment with either compound in the lsd7 F1 plants. Our findings demonstrate that steps early in the signal transduction pathway leading to SAR and disease resistance are potentiated by later events, suggesting feedback control of lesion formation.     

Evolutionary history of almond tree domestication in the Mediterranean basin

Genetic diversity of contemporary domesticated species is shaped by both natural and human‐driven processes. However, until now, little is known about how domestication has imprinted the variation of fruit tree species. In this study, we reconstruct the recent evolutionary history of the domesticated almond tree, Prunus dulcis, around the Mediterranean basin, using a combination of nuclear and chloroplast microsatellites [i.e. simple sequence repeat (SSRs)] to investigate patterns of genetic diversity. Whereas conservative chloroplast SSRs show a widespread haplotype and rare locally distributed variants, nuclear SSRs show a pattern of isolation by distance with clines of diversity from the East to the West of the Mediterranean basin, while Bayesian genetic clustering reveals a substantial longitudinal genetic structure. Both kinds of markers thus support a single domestication event, in the eastern side of the Mediterranean basin. In addition, model‐based estimation of the timing of genetic divergence among those clusters is estimated sometime during the Holocene, a result that is compatible with human‐mediated dispersal of almond tree out of its centre of origin. Still, the detection of region‐specific alleles suggests that gene flow from relictual wild preglacial populations (in North Africa) or from wild counterparts (in the Near East) could account for a fraction of the diversity observed.     

ABCtoolbox: a versatile toolkit for approximate Bayesian computations

Background  

The estimation of demographic parameters from genetic data often requires the computation of likelihoods. However, the likelihood function is computationally intractable for many realistic evolutionary models, and the use of Bayesian inference has therefore been limited to very simple models. The situation changed recently with the advent of Approximate Bayesian Computation (ABC) algorithms allowing one to obtain parameter posterior distributions based on simulations not requiring likelihood computations.