Novel Phosphoinositides in Barley Aleurone Cells (Additional Evidence for the Presence of Phosphatidyl-scyllo-Inositol)

A novel isomer of phosphatidylinositol that differs in the structure of the head group was detected in barley (Hordeum vulgare cv Himalaya) seeds. In this paper we describe our efforts to elucidate the structure of the novel isomer. Evidence from a variety of techniques, including chemical modification of in vivo 32Pi- and myo-[3H]inositol-labeled compounds, gas chromatography-mass spectrometry analysis, in vivo incorporation of scyllo-[3H]inositol, and enzymatic studies that suggest that the structure is phosphatidylscyllo-inositol (scyllo-PI), is presented. The use of microwave energy to significantly enhance the slow rate of hydrolysis of phosphoinositides is described. The presence of scyllo-PI can be easily overlooked by the methods commonly employed; therefore, experimental considerations important for the detection of scyllo-PI are discussed.     

Testing relationships between macroalgal cover and Secchi depth in the Baltic Sea

The present study tests whether relationships between macroalgal cover and water quality, recently developed for Danish coastal waters, are more universal and also applies at the other extreme of the Baltic Sea in Finnish coastal waters. We found that algal cover increases as a function of Secchi depth according to the same logarithmic function in Danish and Finnish coastal waters. Algal cover at a given depth (here modelled for 4 m) increases with increasing Secchi depth and approaches a maximum at the high Secchi depths found in the clearest areas of the Danish coastal waters. For a given Secchi depth the combined Danish/Finnish algal model thus predicts a similar cover of the algal community at a given water depth at both extremes of the Baltic Sea which represent quite different algal habitats. These results suggest that light limitation, and thus shading effects of eutrophication may cause similar reductions of macroalgal cover across ecosystems.     

Computational and Experimental Evidence for the Evolution of a (βα)8-Barrel Protein from an Ancestral Quarter-Barrel Stabilised by Disulfide Bonds

The evolution of the prototypical (βα)₈-barrel protein imidazole glycerol phosphate synthase (HisF) was studied by complementary computational and experimental approaches. The 4-fold symmetry of HisF suggested that its constituting (βα)₂ quarter-barrels have a common evolutionary origin. This conclusion was supported by the computational reconstruction of the HisF sequence of the last common ancestor, which showed that its quarter-barrels were more similar to each other than are those of extant HisF proteins. A comprehensive sequence analysis identified HisF-N1 [corresponding to (βα)_1-2] as the slowest evolving quarter-barrel. This finding indicated that it is the closest relative of the common (βα)₂ predecessor, which must have been a stable and presumably tetrameric protein. In accordance with this prediction, a recombinantly produced HisF-N1 protein was properly folded and formed a tetramer being stabilised by disulfide bonds. The introduction of a disulfide bond in HisF-C1 [corresponding to (βα)_5-6] also resulted in the formation of a stable tetramer. The fusion of two identical HisF-N1 quarter-barrels yielded the stable dimeric half-barrel HisF-N1N1. Our findings suggest a two-step evolutionary pathway in which a HisF-N1-like predecessor was duplicated and fused twice to yield HisF. Most likely, the (βα)₂ quarter-barrel and (βα)₄ half-barrel intermediates on this pathway were stabilised by disulfide bonds that became dispensable upon consolidation of the (βα)₈-barrel.     

Steroid hormone pathways coordinate developmental diapause and olfactory remodeling in Pristionchus pacificus

Developmental and behavioral plasticity allow animals to prioritize alternative genetic programs during fluctuating environments. Behavioral remodeling may be acute in animals that interact with host organisms, since reproductive adults and the developmentally arrested larvae often have different ethological needs for chemical stimuli. To understand the genes that coordinate the development and host-seeking behavior, we used the entomophilic nematode Pristionchus pacificus to characterize dauer-constitutive mutants (Daf-c) that inappropriately enter developmental diapause to become dauer larvae. We found two Daf-c loci with dauer-constitutive and cuticle exsheathment phenotypes that can be rescued by the feeding of Δ7-dafachronic acid, and that are dependent on the conserved canonical steroid hormone receptor Ppa-DAF-12. Specifically at one locus, deletions in the sole hydroxysteroid dehydrogenase (HSD) in P. pacificus resulted in Daf-c phenotypes. Ppa-hsd-2 is expressed in the canal-associated neurons (CANs) and excretory cells whose homologous cells in Caenorhabditis elegans are not known to be involved in the dauer decision. While in wildtype only dauer larvae are attracted to host odors, hsd-2 mutant adults show enhanced attraction to the host beetle pheromone, along with ectopic activation of a marker for putative olfactory neurons, Ppa-odr-3. Surprisingly, this enhanced odor attraction acts independently of the Δ7-DA/DAF-12 module, suggesting that Ppa-HSD-2 may be responsible for several steroid hormone products involved in coordinating the dauer decision and host-seeking behavior in P. pacificus.     

Water clarity and eelgrass responses to nitrogen reductions in the eutrophic Skive Fjord, Denmark

Eelgrass depth limits and water clarity in the Skive Fjord estuarine system have not improved despite nutrient input reductions of 30%. Long-term monitoring data (1989–2010) were used to investigate the underlying causes. Dissolved inorganic and organic nitrogen concentrations decreased significantly over time, whereas particulate organic nitrogen concentration, assumed to consist primarily of phytoplankton and phytoplankton detritus and calculated as a proportional factor to chlorophyll a, did not change. Total organic carbon, mostly of autochthonous origin, remained constant despite reduced nitrogen concentrations, resulting in an increasing C:N ratio of the organic material in the water column. Phytoplankton primary production also remained constant suggesting that phytoplankton growth was only limited by nitrogen to a minor degree. Alleviated grazing pressure caused by a reduction in the blue mussel standing stock and a pelagic food web dominated by jellyfish may have contributed to the constantly high phytoplankton levels. Particulate inorganic matter, likely reflecting sediment resuspension, increased over time, most probably in response to removal of blue mussels and declining eelgrass cover. The Skive Fjord estuarine system is affected by multiple pressures—nutrient enrichment, mussel dredging and climate change that must be addressed together for water clarity to improve and eelgrass to recover.     

Determinants of bird species richness,endemism, and island network roles in Wallacea and the West Indies: is geography sufficient or does current and historical climate matter?

Island biogeography has greatly contributed to our understanding of the processes determining species' distributions. Previous research has focused on the effects of island geography (i.e., island area, elevation, and isolation) and current climate as drivers of island species richness and endemism. Here, we evaluate the potential additional effects of historical climate on breeding land bird richness and endemism in Wallacea and the West Indies. Furthermore, on the basis of species distributions, we identify island biogeographical network roles and examine their association with geography, current and historical climate, and bird richness/endemism. We found that island geography, especially island area but also isolation and elevation, largely explained the variation in island species richness and endemism. Current and historical climate only added marginally to our understanding of the distribution of species on islands, and this was idiosyncratic to each archipelago. In the West Indies, endemic richness was slightly reduced on islands with historically unstable climates; weak support for the opposite was found in Wallacea. In both archipelagos, large islands with many endemics and situated far from other large islands had high importance for the linkage within modules, indicating that these islands potentially act as speciation pumps and source islands for surrounding smaller islands within the module and, thus, define the biogeographical modules. Large islands situated far from the mainland and/or with a high number of nonendemics acted as links between modules. Additionally, in Wallacea, but not in the West Indies, climatically unstable islands tended to interlink biogeographical modules. The weak and idiosyncratic effect of historical climate on island richness, endemism, and network roles indicates that historical climate had little effects on extinction‐immigration dynamics. This is in contrast to the strong effect of historical climate observed on the mainland, possibly because surrounding oceans buffer against strong climate oscillations and because geography is a strong determinant of island richness, endemism and network roles.     

A welcome can of worms? Hypoxia mitigation by an invasive species

Invasive species and bottom‐water hypoxia both constitute major global threats to the diversity and integrity of marine ecosystems. These stressors may interact with unexpected consequences, as invasive species that require an initial environmental disturbance to become established can subsequently become important drivers of ecological change. There is recent evidence that improved bottom‐water oxygen conditions in coastal areas of the northern Baltic Sea coincide with increased abundances of the invasive polychaetes Marenzelleria spp. Using a reactive‐transport model, we demonstrate that the long‐term bioirrigation activities of dense Marenzelleria populations have a major impact on sedimentary phosphorus dynamics. This may facilitate the switch from a seasonally hypoxic system back to a normoxic system by reducing the potential for sediment‐induced eutrophication in the upper water column. In contrast to short‐term laboratory experiments, our simulations, which cover a 10‐year period, show that Marenzelleria has the potential to enhance long‐term phosphorus retention in muddy sediments. Over time bioirrigation leads to a substantial increase in the iron‐bound phosphorus content of sediments while reducing the concentration of labile organic carbon. As surface sediments are maintained oxic, iron oxyhydroxides are able to persist and age into more refractory forms. The model illustrates mechanisms through which Marenzelleria can act as a driver of ecological change, although hypoxic disturbance or natural population declines in native species may be needed for them to initially become established. Invasive species are generally considered to have a negative impact; however, we show here that one of the main recent invaders in the Baltic Sea may provide important ecosystem services. This may be of particular importance in low‐diversity systems, where disturbances may dramatically alter ecosystem services due to low functional redundancy. Thus, an environmental problem in one region may be either exacerbated or alleviated by a single species from another region, with potentially ecosystem‐wide consequences.     

Effect of Incubation Conditions on the Enrichment of Pyrene-degrading Bacteria Identified by Stable-isotope Probing in an Aged,PAH-contaminated Soil

To determine whether the diversity of pyrene-degrading bacteria in an aged polycyclic aromatic hydrocarbon-contaminated soil is affected by the addition of inorganic nutrients or by slurrying the soil, various incubation conditions (all including phosphate buffer) were examined by mineralization studies and stable-isotope probing (SIP). The addition of nitrogen to either continuously mixed slurry or static field-wet soil incubations increased the rate and extent of mineralization of [(14)C]pyrene, with the most rapid mineralization observed in slurried, nitrogen-amended soil. Microcosms of slurry and static field-wet soil amended with nitrogen were also examined by SIP with [U-(13)C]pyrene. Recovered (13)C-enriched deoxyribonucleic acid (DNA) was analyzed by denaturing-gradient gel electrophoresis (DGGE) and 16S ribosomal ribonucleic acid (rRNA) gene clone libraries. DGGE profiles of (13)C-enriched DNA fractions from both incubation conditions were similar, suggesting that pyrene-degrading bacterial community diversity may be independent of treatment method. The vast majority (67 of 71) of the partial sequences recovered from clone libraries were greater than or equal to 97% similar to one another, 98% similar to sequences of pyrene-degrading bacteria previously detected by SIP with pyrene in different soil, and only 89% similar to the closest cultivated genus. All of the sequences recovered from the field-wet incubation and most of the sequences recovered from the slurry incubation were in this clade. Of the four sequences from slurry incubations not within this clade, three possessed greater than 99% similarity to the 16S rRNA gene sequences of phylogenetically dissimilar Caulobacter spp.