The marine macroalgae of Helgoland (North Sea): an annotated list of records between 1845 and 1999

The earliest known records of marine macroalgae from Helgoland (German Bight, North Sea) date from the mid-19th century. Since then, 274 marine macroalgal species have been reported: 77 species of Chlorophycota, 100 species of Phaeophycota and 97 species of Rhodophycota. Additionally 11 species were only recorded as drift and 51 species as doubtful for Helgoland. The remains of the herbarium of Paul Kuckuck, the first curator for botany at the Helgoland Biological Station between 1892 and 1914, are still located there and consist of 173 macroalgal species from Helgoland. On comparing this 100-year-old herbarium and other old sources with recent macroalgal records, it became clear that changes in species composition have occurred. After World War II, several species such as Arthrocladia villosa, Corynophlaea crispa, Cutleria multifida, Eudesme virescens, Mesogloia vermiculata, Sporochnus pedunculatus, Antithamnion cruciatum, Apoglossum ruscifolium, Chondria dasyphylla, Helminthora divaricata, Jania rubens and Osmundea ramosissima were not found again. Other species such as Dictyota dichotoma, Leathesia difformis, Stictyosiphon soriferus, Helminthocladia calvadosii and Scinaia furcellata became very rare. Significantly, perhaps, most of these species have a heteromorphic life history with the appearance of the macroscopic phase restricted to (spring and) summer. Many new species of green algae were recorded for Helgoland after 1959, due to new substrata and the research activities of Peter Kornmann, curator for botany after 1959, and Paul-Heinz Sahling his technical assistant. Introductions of species during the considered time period were: Bonnemaisonia hamifera, Codium fragile, Mastocarpus stellatus and Sargassum muticum. Type material of the following species is located at the Marine Biological Station at Helgoland: Mikrosyphar porphyrae, Porphyra insolita and Ulva tenera. Received in revised form: 22 May 2000 Electronic Publication     

Arginine Depletion by Arginine Deiminase Does Not Affect Whole Protein Metabolism or Muscle Fractional Protein Synthesis Rate in Mice

Due to the absolute need for arginine that certain cancer cells have, arginine depletion is a therapy in clinical trials to treat several types of cancers. Arginine is an amino acids utilized not only as a precursor for other important molecules, but also for protein synthesis. Because arginine depletion can potentially exacerbate the progressive loss of body weight, and especially lean body mass, in cancer patients we determined the effect of arginine depletion by pegylated arginine deiminase (ADI-PEG 20) on whole body protein synthesis and fractional protein synthesis rate in multiple tissues of mice. ADI-PEG 20 successfully depleted circulating arginine (<1 μmol/L), and increased citrulline concentration more than tenfold. Body weight and body composition, however, were not affected by ADI-PEG 20. Despite the depletion of arginine, whole body protein synthesis and breakdown were maintained in the ADI-PEG 20 treated mice. The fractional protein synthesis rate of muscle was also not affected by arginine depletion. Most tissues (liver, kidney, spleen, heart, lungs, stomach, small and large intestine, pancreas) were able to maintain their fractional protein synthesis rate; however, the fractional protein synthesis rate of brain, thymus and testicles was reduced due to the ADI-PEG 20 treatment. Furthermore, these results were confirmed by the incorporation of ureido [¹⁴C]citrulline, which indicate the local conversion into arginine, into protein. In conclusion, the intracellular recycling pathway of citrulline is able to provide enough arginine to maintain protein synthesis rate and prevent the loss of lean body mass and body weight.     

High maternal species density mediates unidirectional heterospecific matings in Calopteryx damselflies

Hybridization is a well‐known phenomenon, but there are still relatively few studies addressing the question of reproductive isolation between related sympatric animal species with largely overlapping ranges. Population density, relative abundance, and operational sex ratio (OSR) are among the factors known to have an influence on the frequency of heterospecific matings in sympatric populations. Here we had two aims. First, we used microsatellite markers and field observations to study the frequency of hybrids, and backcrosses, and the rate of heterospecific matings between two sympatric damselfly species Calopteryx splendens (Harris, 1780) and Calopteryx virgo (Linné, 1758). Second, we investigated the role of population densities, relative abundances, and OSRs on conspecific and heterospecific mating rates. Altogether we genotyped 2104 individuals from both species and found four hybrids (0.19%), one of which was a backcross. Of all the 272 matings observed, 17 (6%) were between heterospecifics, and all of these were between a C. splendens male and a C. virgo female. In addition, all of the hybrids contained mitochondrial DNA (mtDNA) of C. virgo. We show that the population density of C. virgo, which was the maternal species of all the heterospecific matings and hybrid individuals, was the only significant factor covarying with the rate of the heterospecific matings. The OSRs did not correlate with the rate of con‐ or heterospecific matings. Studies on interspecific interactions in sympatric species can give information about the maintenance of reproductive isolation, and thus speciation. © 2012 The Linnean Society of London     

Enteral arginase II provides ornithine for citrulline synthesis

The synthesis of citrulline from arginine in the small intestine depends on the provision of ornithine. To test the hypothesis that arginase II plays a central role in the supply of ornithine for citrulline synthesis, the contribution of dietary arginine, glutamine, and proline was determined by utilizing multitracer stable isotope protocols in arginase II knockout (AII(-/-)) and wild-type (WT) mice. The lack of arginase II resulted in a lower citrulline rate of appearance (121 vs. 137 μmol·kg(-1)·h(-1)) due to a reduced availability of ornithine; ornithine supplementation was able to restore the rate of citrulline production in AII(-/-) to levels comparable with WT mice. There were significant differences in the utilization of dietary citrulline precursors. The contribution of dietary arginine to the synthesis of citrulline was reduced from 45 to 10 μmol·kg(-1)·h(-1) due to the lack of arginase II. No enteral utilization of arginine was observed in AII(-/-) mice (WT = 25 μmol·kg(-1)·h(-1)), and the contribution of dietary arginine through plasma ornithine was reduced in the transgenic mice (20 vs. 13 μmol·kg(-1)·h(-1)). Dietary glutamine and proline utilization were greater in AII(-/-) than in WT mice (20 vs. 13 and 1.4 vs. 3.7 μmol·kg(-1)·h(-1), respectively). Most of the contribution of glutamine and proline was enteral rather than through plasma ornithine. The arginase isoform present in the small intestinal mucosa has the role of providing ornithine for citrulline synthesis. The lack of arginase II results in a greater contribution of plasma ornithine and dietary glutamine and proline to the synthesis of citrulline.     

Rho proteins of plants--functional cycle and regulation of cytoskeletal dynamics

Rho-related ROP proteins are molecular switches that essentially regulate a wide variety of processes. Of central interest is their influence on the plant cytoskeleton by which they affect vital processes like cell division, growth, morphogenesis, and pathogen defense. ROPs switch between GTP- and GDP-bound conformations by strictly regulated nucleotide exchange and GTP-hydrolysis, and only the active GTP-form interacts with downstream effectors to ultimately provoke a biological response. However, the mode of action of the engaged regulators and effectors as well as their upstream and downstream interaction partners have long been largely unknown. As opposed to analogous systems in animals and fungi, plants use specific GTPase activating proteins (RopGAPs) with a unique domain composition and novel guanine nucleotide exchange factors (RopGEFs) with a probable link to cell surface receptors. Moreover, plants comprise novel effector molecules and adapters connecting ROPs to mostly unknown downstream targets on the route to the cytoskeleton. This review aims to summarize recent knowledge on the molecular mechanisms and reaction cascades involved in ROP dependent cytoskeletal rearrangements, addressing the structure and function of the unusual RopGAPs, RopGEFs and effectors, and the upstream and downstream pathways linking ROPs to cell receptor-like kinases, actin filaments, and microtubules.     

The phosphomimetic mutation of an evolutionarily conserved serine residue affects the signaling properties of Rho of plants (ROPs)

Plant ROP (Rho of plants) proteins form a unique subgroup within the family of Rho-type small G-proteins of eukaryotes. In this paper we demonstrate that the phosphomimetic mutation of a serine residue conserved in all Rho proteins affects the signaling properties of plant ROPs. We found that the S74E mutation in Medicago ROP6 and Arabidopsis ROP4 prevented the binding of these proteins to their plant-specific upstream activator the plant-specific ROP nucleotide exchanger (PRONE)-domain-containing RopGEF (guanine nucleotide exchange factor) protein and abolished the PRONE-mediated nucleotide exchange reaction in vitro. Structural modeling supported the hypothesis that potential phosphorylation of the S74 residue interferes with the binding of the PRONE-domain to the adjacent plant-specific R76 residue which plays an important role in functional ROP-PRONE interaction. Moreover, we show that while the binding of constitutively active MsROP6 to the effector protein RIC (ROP-interactive CRIB-motif-containing protein) was not affected by the S74E mutation, the capability of this mutated protein to bind and activate the RRK1 kinase in vitro was reduced. These observations are in agreement with the morphology of tobacco pollen tubes expressing mutant forms of yellow fluorescent protein (YFP):MsROP6. The S74E mutation in MsROP6 had no influence on pollen tube morphology and attenuated the phenotype of a constitutively active form of MsROP6. The presented Medicago and Arabidopsis data support the notion that the phosphorylation of the serine residue in ROPs corresponding to S74 in Medicago ROP6 could be a general principle for regulating ROP activation and signaling in plants.     

Biochemical characterization of UDP-Gal:GlcNAc-pyrophosphate-lipid β-1,4-Galactosyltransferase WfeD, a new enzyme from Shigella boydii type 14 that catalyzes the second step in O-antigen repeating-unit synthesis

The O antigen is the outer part of the lipopolysaccharide (LPS) in the outer membrane of Gram-negative bacteria and contains many repeats of an oligosaccharide unit. It contributes to antigenic variability and is essential to the full function and virulence of bacteria. Shigella is a Gram-negative human pathogen that causes diarrhea in humans. The O antigen of Shigella boydii type 14 consists of repeating oligosaccharide units with the structure [→6-d-Galpα1→4-d-GlcpAβ1→6-d-Galpβ1→4-d-Galpβ1→4-d-GlcpNAcβ1→]n. The wfeD gene in the O-antigen gene cluster of Shigella boydii type 14 was proposed to encode a galactosyltransferase (GalT) involved in O-antigen synthesis. We confirmed here that the wfeD gene product is a β4-GalT that synthesizes the Galβ1-4GlcNAcα-R linkage. WfeD was expressed in Escherichia coli, and the activity was characterized by using UDP-[³H]Gal as the donor substrate as well as the synthetic acceptor substrate GlcNAcα-pyrophosphate-(CH₂)₁₁-O-phenyl. The enzyme product was analyzed by liquid chromatography-mass spectrometry (LC-MS), high-performance liquid chromatography (HPLC), nuclear magnetic resonance (NMR), and galactosidase digestion. The enzyme was shown to be specific for the UDP-Gal donor substrate and required pyrophosphate in the acceptor substrate. Divalent metal ions such as Mn²⁺, Ni²⁺, and, surprisingly, also Pb²⁺ enhanced the enzyme activity. Mutational analysis showed that the Glu101 residue within a DxD motif is essential for activity, possibly by forming the catalytic nucleophile. The Lys211 residue was also shown to be required for activity and may be involved in the binding of the negatively charged acceptor substrate. Our study revealed that the β4-GalT WfeD is a novel enzyme that has virtually no sequence similarity to mammalian β4-GalT, although it catalyzes a similar reaction.Lipopolysaccharides (LPSs) consist of O-polysaccharide (O-antigenic) side chains covalently linked to a core polysaccharide and lipid A. LPSs are found in the outer membranes of Gram-negative bacteria, where they contribute to the structural integrity of the membrane and interact with the external environment (9, 10, 15). In the complex and dynamic microbial ecosystem of the human intestine, the communication between microorganisms and the gastrointestinal (GI) epithelium involves O-antigen and LPS binding molecules. Thus, the elimination of the O antigen may reduce virulence (2, 16, 21). Shigella is a genus of highly adapted bacterial pathogens that cause gastrointestinal disease, such as bacillary dysentery or shigellosis. A recent survey showed that shigellosis causes approximately 165 million cases of severe dysentery and more than 1 million deaths per year, mostly in children from developing countries (10). Shigella strains are categorized into four groups: S. boydii, S. dysenteriae, S. flexneri, and S. sonnei, each containing multiple subgroups of different serotypes, based on structural variations in their O antigens.O antigens consist of repeating units of oligosaccharides that are assembled individually, followed by the polymerization of units to form O antigens of different lengths. The glycosyltransferases involved in the biosynthesis of O antigens play a critical role in determining O-antigen structural diversity. The pentasaccharide repeating unit of S. boydii type 14 (B14) has the structure [→6-d-Galpα1→4-d-GlcpAβ1→6-d-Galpβ1→4-d-Galpβ1→4-d-GlcpNAcβ1→]n (12), suggesting the existence of five specific glycosyltransferases: a GlcNAc-phosphotransferase (WecA), three Gal-transferases, and a glucuronosyltransferase.Three distinct processes for the synthesis and translocation of O antigens have been described: the Wzx/Wzy-dependent pathway, the ATP binding cassette transporter-dependent process, and the synthase-dependent process (20, 25, 26). The biosynthesis of the S. boydii B14 O antigen that contains a variety of different sugar residues is expected to utilize the Wzy/Wzx-dependent pathway, where the synthesis of the repeating unit is initiated by WecA, catalyzing the transfer of sugar-phosphate (GlcNAcα-phosphate) from nucleotide sugar (UDP-GlcNAc) to a lipid carrier, undecaprenol-phosphate (Und-P), at the cytoplasmic side of the inner membrane. The wecA gene is present in the S. boydii B14 genome but outside the O-antigen gene cluster (1). The wecA gene is also involved in the synthesis of bacterial polysaccharides other than the O antigen. The extension of the chain is then mediated by specific glycosyltransferases that utilize nucleotide sugar donor substrates and are thought to be loosely associated with the inner membrane. In contrast, mammalian glycosyltransferases are usually membrane-bound proteins. Bacterial and mammalian glycosyltransferases, although they may have similar substrate specificities and form the same linkage, show significantly different amino acid sequences (4). Completed repeating units are then flipped across the membrane to the periplasmic side (by the flippase Wzx) and are polymerized (by Wzy) to form the O antigen under the control of a chain length regulator (Wzz). The repeating units are initially linked to the lipid carrier through GlcNAcα-phosphate. However, the S. boydii B14 O antigen has GlcNAc in the β linkage; thus, upon the polymerization of the completed repeating units, the linkage may be inverted, probably through the specific action of the polymerase Wzy. The entire polymer is then ligated to an outer core sugar based on lipid A. Upon completion, the LPS is extruded from the inner membrane and translocated to the outer membrane (19, 26). The latter-acting enzymes have multiple transmembrane regions that integrate them into the bacterial membranes.Genes involved in O-antigen biosynthesis are normally clustered between galF and gnd in Escherichia coli and Shigella and are classified into three different groups: (i) nucleotide sugar synthesis genes involved in the synthesis of donor substrates, (ii) glycosyltransferase genes, and (iii) O-antigen-processing genes, such as the flippase gene wzx and the polymerase gene wzy. The O-antigen gene cluster of B14 has been sequenced and analyzed (10). Four putative glycosyltransferase genes found in the B14 O-antigen synthesis gene cluster are wfeA, wfeB, wfeD, and wfeE. WfeD shares 38% identity and 57% similarity to the putative glycosyltransferase Orf9, which is involved in the synthesis of the E. coli O136 O antigen (our unpublished data). Since the O antigens of B14 and E. coli O136 share only one common linkage, d-Galpβ1→4-d-GlcpNAc (12, 23), wfeD was proposed to encode the galactosyltransferase (GalT) that transfers Gal to GlcNAcα-PP-Und in the β1-4 linkage, which is the second step in the biosynthetic pathway of the B14 O-antigen repeating unit.We have used biochemical approaches to assay the WfeD enzyme activity and to characterize this enzyme. The lipid carrier analog GlcNAcα-PO₃-PO₃-(CH₂)₁₁-O-phenyl [GlcNAc-PP-(CH₂)₁₁-OPh] has previously been used as a defined synthetic acceptor substrate for the characterization of glycosyltransferases from E. coli serotypes O7 (β1,3-GalT WbbD), O56 (β1,3-Glc-transferase WfaP), and O152 (β1,3-Glc-transferase WfgD) (6, 17). In this work, we showed that GlcNAc-PP-(CH₂)₁₁-OPh could also serve as an exogenous substrate for WfeD from B14. We were therefore able to prove that wfeD encodes a novel β1,4-GalT.     

Loss of a chloroplast encoded function could influence species range in kelp

Kelps are important providers and constituents of marine ecological niches, the coastal kelp forests. Kelp species have differing distribution ranges, but mainly thrive in temperate and arctic regions. Although the principal factors determining biogeographic distribution ranges are known, genomics could provide additional answers to this question. We sequenced DNA from two Laminaria species with contrasting distribution ranges, Laminaria digitata and Laminaria solidungula. Laminaria digitata is found in the Northern Atlantic with a southern boundary in Brittany (France) or Massachusetts (USA) and a northern boundary in the Arctic, whereas L. solidungula is endemic to the Arctic only. From the raw reads of DNA, we reconstructed both chloroplast genomes and annotated them. A concatenated data set of all available brown algae chloroplast sequences was used for the calculation of a robust phylogeny, and sequence variations were analyzed. The two Laminaria chloroplast genomes are collinear to previously analyzed kelp chloroplast genomes with important exceptions. Rearrangements at the inverted repeat regions led to the pseudogenization of ycf37 in L. solidungula, a gene possibly required under high light conditions. This defunct gene might be one of the reasons why the habitat range of L. solidungula is restricted to lowlight sublittoral sites in the Arctic. The inheritance pattern of single nucleotide polymorphisms suggests incomplete lineage sorting of chloroplast genomes in kelp species. Our analysis of kelp chloroplast genomes shows that not only evolutionary information could be gleaned from sequence data. Concomitantly, those sequences can also tell us something about the ecological conditions which are required for species well‐being.