Nazca Booby (Sula granti) inputs maintain the terrestrial food web of Malpelo Island

Most of the known food webs are based on organic compounds provided by photoautotrophic organisms. The terrestrial ecosystem of Malpelo Island (Colombia) seems to be an exception, however, since it supports several trophic guilds without hosting an adequate amount of primary producers. It has been suggested that this apparent paradox might be explained by external inputs provided by seabirds, namely Nazca Boobies (Sula granti), forming a huge colony on Malpelo. This hypothesis has never been tested. Here, we present a first approach to quantify the significance of Nazca Booby inputs into the Malpelo ecosystem via excrement, second eggs/chicks (which are prone to die), and carcasses, respectively, during the major breeding season. The total input was calculated to amount to 171.6 t per breeding season, with excrements accounting for almost 99% (170 t) of this input. Second eggs/chicks contributed approximately 1.1 t (0.64%) and carcasses around 0.1 t (0.06%). These finding support the idea of the Nazca Booby facilitating a food chain that pairs the pelagic primary producers of the open ocean with the terrestrial consumers of an island. Species most strongly profiting from this process include three endemic lizard species (Anolis agassizi, Diploglossus millepunctatus, Phyllodactylus transversalis) and the land crab (Johngarthia malpilensis).     

How do soil fauna and soil microbiota respond to beech forest growth?

The dynamics and performance of soil biota during forest rotation were studied in monoculture beech stands forming a chronosequence of four different age-classes(30,62,111,153 yr).Biomass was monitored in major groups of microflora,microfauna,mesofauna,and macrofauna.Resource availability(litter layer,soil organic mater),biomass of the two dominant decomposer groups(microflora,earthworms)as well as the biomass of mesofauna and microfauna were found to remain quite stable during forest succession.Nevertheles...     

Oligomeric structure of ExbB and ExbB-ExbD isolated from Escherichia coli as revealed by LILBID mass spectrometry

Energy-coupled transporters in the outer membrane of Escherichia coli and other Gram-negative bacteria allow the entry of scarce substrates, toxic proteins, and bacterial viruses (phages) into the cells. The required energy is derived from the proton-motive force of the cytoplasmic membrane, which is coupled to the outer membrane via the ExbB-ExbD-TonB protein complex. Knowledge of the structure of this complex is required to elucidate the mechanisms of energy harvesting in the cytoplasmic membrane and energy transfer to the outer membrane transporters. Here we solubilized an ExbB oligomer and an ExbB-ExbD subcomplex from the cytoplasmic membrane with the detergent undecyl maltoside. Using laser-induced liquid bead ion desorption mass spectrometry (LILBID-MS), we determined at moderate desorption laser energies the oligomeric structure of ExbB to be mainly hexameric (ExbB(6)), with minor amounts of trimeric (ExbB(3)), dimeric (ExbB(2)), and monomeric (ExbB(1)) oligomers. Under the same conditions ExbB-ExbD formed a subcomplex consisting of ExbB(6)ExbD(1), with a minor amount of ExbB(5)ExbD(1). At higher desorption laser intensities, ExbB(1) and ExbD(1) and traces of ExbB(3)ExbD(1), ExbB(2)ExbD(1), ExbB(1)ExbD(1), ExbB(3), and ExbB(2) were observed. Since the ExbB(6) complex and the ExbB(6)ExbD(1) complex remained stable during solubilization and subsequent chromatographic purification on nickel-nitrilotriacetate agarose, Strep-Tactin, and Superdex 200, and during native blue gel electrophoresis, we concluded that ExbB(6) and ExbB(6)ExbD(1) are subcomplexes on which the final complex including TonB is assembled.     

Effects of low frequency electromagnetic fields on the chondrogenic differentiation of human mesenchymal stem cells

Electromagnetic fields (EMF) have been shown to exert beneficial effects on cartilage tissue. Nowadays, differentiated human mesenchymal stem cells (hMSCs) are discussed as an alternative approach for cartilage repair. Therefore, the aim of this study was to examine the impact of EMF on hMSCs during chondrogenic differentiation. HMSCs at cell passages five and six were differentiated in pellet cultures in vitro under the addition of human fibroblast growth factor 2 (FGF‐2) and human transforming growth factor‐β₃ (TGF‐β₃). Cultures were exposed to homogeneous sinusoidal extremely low‐frequency magnetic fields (5 mT) produced by a solenoid or were kept in a control system. After 3 weeks of culture, chondrogenesis was assessed by toluidine blue and safranin‐O staining, immunohistochemistry, quantitative real‐time polymerase chain reaction (PCR) for cartilage‐specific proteins, and a DMMB dye‐binding assay for glycosaminoglycans. Under EMF, hMSCs showed a significant increase in collagen type II expression at passage 6. Aggrecan and SOX9 expression did not change significantly after EMF exposure. Collagen type X expression decreased under electromagnetic stimulation. Pellet cultures at passage 5 that had been treated with EMF provided a higher glycosaminoglycan (GAG)/DNA content than cultures that had not been exposed to EMF. Chondrogenic differentiation of hMSCs may be improved by EMF regarding collagen type II expression and GAG content of cultures. EMF might be a way to stimulate and maintain chondrogenesis of hMSCs and, therefore, provide a new step in regenerative medicine regarding tissue engineering of cartilage. Bioelectromagnetics 32:283–290, 2011. © 2010 Wiley‐Liss, Inc.     

Scaling properties of multivariate landscape structure

Analyses of landscape context is essential for understanding how ecological patterns and processes relate to space. This requires that we quantify variation patterns of different landscape parameters, which may change relative to one another at different spatial scales. Here, we analyzed how statistical relationships of land-use composition parameters changed as a function of extent in 20 real agricultural landscapes. Furthermore, we tested the generality of these scaling relations in numerical simulations using 300 artificial landscapes. We analyzed proportions of artificial habitat types at different extent and compared these patterns with three dominant habitat types in real landscapes (forest, arable land and grassland) at four spatial scales (quadrates of 1–4 km). Both real and simulated landscapes showed that variance of landscape parameters (data differentiation) decreased and their correlations (data consistency) increased as scale increased, thereby suggesting general scaling laws. The potential statistical impact of these scaling relationships is revealed in simultaneous analyses of variation of (local) site parameters of 20 arable fields and their surrounding landscape context. At small and medium extent (quadrates of 1–3 km), variability of local site parameters (e.g. fertilization, pH-value) was high relative to those of landscape parameters. In contrast, at large extent (quadrates of 4 km) variability of landscape parameters was greater than that of site parameters indicating a fundamental shift in the relationship between these sets of parameters at different scales. Hence, it is clear that there is a high risk of artefactual correlations in hierarchical multi-scale landscape analyses when ecological data are related to the landscape context. Accordingly, there is a necessity for multi-scale analyses in landscape ecology to accurately evaluate the relative importance of landscape context at different spatial scales.     

The Vi Capsular Polysaccharide Enables Salmonella enterica Serovar Typhi to Evade Microbe-Guided Neutrophil Chemotaxis

Salmonella enterica serovar Typhi (S. Typhi) causes typhoid fever, a disseminated infection, while the closely related pathogen S. enterica serovar Typhimurium (S. Typhimurium) is associated with a localized gastroenteritis in humans. Here we investigated whether both pathogens differ in the chemotactic response they induce in neutrophils using a single-cell experimental approach. Surprisingly, neutrophils extended chemotactic pseudopodia toward Escherichia coli and S. Typhimurium, but not toward S. Typhi. Bacterial-guided chemotaxis was dependent on the presence of complement component 5a (C5a) and C5a receptor (C5aR). Deletion of S. Typhi capsule biosynthesis genes markedly enhanced the chemotactic response of neutrophils in vitro. Furthermore, deletion of capsule biosynthesis genes heightened the association of S. Typhi with neutrophils in vivo through a C5aR-dependent mechanism. Collectively, these data suggest that expression of the virulence-associated (Vi) capsular polysaccharide of S. Typhi obstructs bacterial-guided neutrophil chemotaxis.     

Gene Cluster Involved in the Biosynthesis of Griseobactin,a Catechol-Peptide Siderophore of Streptomyces sp. ATCC 700974

The main siderophores produced by streptomycetes are desferrioxamines. Here we show that Streptomyces sp. ATCC 700974 and several Streptomyces griseus strains, in addition, synthesize a hitherto unknown siderophore with a catechol-peptide structure, named griseobactin. The production is repressed by iron. We sequenced a 26-kb DNA region comprising a siderophore biosynthetic gene cluster encoding proteins similar to DhbABCEFG, which are involved in the biosynthesis of 2,3-dihydroxybenzoate (DHBA) and in the incorporation of DHBA into siderophores via a nonribosomal peptide synthetase. Adjacent to the biosynthesis genes are genes that encode proteins for the secretion, uptake, and degradation of siderophores. To correlate the gene cluster with griseobactin synthesis, the dhb genes in ATCC 700974 were disrupted. The resulting mutants no longer synthesized DHBA and griseobactin; production of both was restored by complementation with the dhb genes. Heterologous expression of the dhb genes or of the entire griseobactin biosynthesis gene cluster in the catechol-negative strain Streptomyces lividans TK23 resulted in the synthesis and secretion of DHBA or griseobactin, respectively, suggesting that these genes are sufficient for DHBA and griseobactin biosynthesis. Griseobactin was purified and characterized; its structure is consistent with a cyclic and, to a lesser extent, linear form of the trimeric ester of 2,3-dihydroxybenzoyl-arginyl-threonine complexed with aluminum under iron-limiting conditions. This is the first report identifying the gene cluster for the biosynthesis of DHBA and a catechol siderophore in Streptomyces.Iron is an essential element for the growth and proliferation of nearly all microorganisms. In the presence of oxygen, the soluble ferrous iron is readily oxidized to its ferric form, which exists predominantly as a highly insoluble hydroxide complex at neutral pH. To overcome iron limitation, many bacteria synthesize and secrete low-molecular-weight, high-affinity ferric iron chelators, called siderophores (38, 53). Following the chelation of Fe³⁺ in the medium, the iron-siderophore complex is actively taken up by its cognate ABC transport system, and Fe³⁺ is subsequently released by reduction to Fe²⁺ and/or by hydrolysis of the siderophore (28, 32, 36). The three main classes of siderophores contain catecholates, hydroxamates, or (α-hydroxy-)carboxylates as iron-coordinating ligands, but mixed siderophores and siderophores containing other functional groups, such as diphenolates, imidazoles, and thiazolines, have also been found (16, 38).Siderophores containing peptide moieties are synthesized by proteins belonging to the nonribosomal peptide synthetase (NRPS) family (16, 38). These multimodular enzymes function as enzymatic assembly lines in which the order of the modules usually determines the order of the amino acids incorporated into the peptide (19, 34). Each module contains the complete information for an elongation step combining the catalytic functions for the activation of the amino acid by the adenylation (A) domain, the tethering of the corresponding adenylate to the terminal thiol of the enzyme-bound 4′-phosphopantetheinyl (4′-PP) cofactor by the peptidyl carrier protein (PCP) domain, and the formation of the peptide bond by the condensation (C) domain (26, 34, 52). At the end, the product is released by the C-terminal thioesterase (TE) domain by hydrolysis or by cyclization via intramolecular condensation. Each adenylation domain recognizes a specific amino acid, and its substrate specificity can be predicted by its sequence. An NRPS specificity-conferring code consisting of 10 nonadjacent amino acid residues in the A domain has been proposed (49). Exceptions to the “colinearity-rule” (19) have been discovered. For example, in the biosynthesis of the siderophores enterobactin and bacillibactin, all the modules in the NRPS are used iteratively, and the TE domain stitches the chains together into a cyclic product (35, 45). Enterobactin is the trilactone of 2,3-dihydroxybenzoyl-serine, and bacillibactin is the lactone of 2,3-dihydroxybenzoyl-glycyl-threonine.The typical siderophores produced by streptomycetes are desferrioxamines (24), and the genes encoding the enzymes for their biosynthesis have been identified (5). Recently, structurally different siderophores have been reported to be coproduced with desferrioxamines in some species, e.g., coelichelin in Streptomyces coelicolor (9, 30) and enterobactin in Streptomyces tendae (18). The genes encoding the proteins for the biosynthesis of enterobactin in S. tendae remain unknown.Here we describe the gene cluster for the biosynthesis of a new siderophore, named griseobactin, produced by Streptomyces sp. strain ATCC 700974 and some strains of Streptomyces griseus. By sequencing two cosmids isolated from a Streptomyces sp. strain ATCC 700974 genomic library, we assigned the encoded proteins to enzymes that convert chorismate to 2,3-dihydroxybenzoate (DHBA), and to proteins involved in nonribosomal peptide biosynthesis and in the export, uptake, and utilization of siderophores. Knockout mutagenesis and heterologous expression confirmed the requirement of this gene cluster for the biosynthesis of griseobactin. This is the first report on the identification of the genes responsible for DHBA and catechol siderophore biosynthesis in Streptomyces.     

Dermal application of nitric oxide releasing acidified nitrite-containing liniments significantly reduces blood pressure in humans

Vascular ischemic diseases, hypertension, and other systemic hemodynamic and vascular disorders may be the result of impaired bioavailability of nitric oxide (NO). NO but also its active derivates like nitrite or nitroso compounds are important effector and signal molecules with vasodilating properties. Our previous findings point to a therapeutical potential of cutaneous administration of NO in the treatment of systemic hemodynamic disorders. Unfortunately, no reliable data are available on the mechanisms, kinetics and biological responses of dermal application of nitric oxide in humans in vivo. The aim of the study was to close this gap and to explore the therapeutical potential of dermal nitric oxide application. We characterized with human skin in vitro and in vivo the capacity of NO, applied in a NO-releasing acidified form of nitrite-containing liniments, to penetrate the epidermis and to influence local as well as systemic hemodynamic parameters. We found that dermal application of NO led to a very rapid and significant transepidermal translocation of NO into the underlying tissue. Depending on the size of treated skin area, this translocation manifests itself through a significant systemic increase of the NO derivates nitrite and nitroso compounds, respectively. In parallel, this translocation was accompanied by an increased systemic vasodilatation and blood flow as well as reduced blood pressure. We here give evidence that in humans dermal application of NO has a therapeutic potential for systemic hemodynamic disorders that might arise from local or systemic insufficient availability of NO or its bio-active NO derivates, respectively.