An excess of massive stars in the local 30 Doradus starburst.

The 30 Doradus star-forming region in the Large Magellanic Cloud is a nearby analog of large star-formation events in the distant universe. We determined the recent formation history and the initial mass function (IMF) of massive stars in 30 Doradus on the basis of spectroscopic observations of 247 stars more massive than 15 solar masses ([Formula: see text]). The main episode of massive star formation began about 8 million years (My) ago, and the star-formation rate seems to have declined in the last 1 My. The IMF is densely sampled up to 200 [Formula: see text] and contains 32 ± 12% more stars above 30 [Formula: see text] than predicted by a standard Salpeter IMF. In the mass range of 15 to 200 [Formula: see text], the IMF power-law exponent is [Formula: see text], shallower than the Salpeter value of 2.35.

Converting Wannier into Frenkel excitons in an inorganic/organic hybrid semiconductor nanostructure.

Electronic coupling between Wannier and Frenkel excitons in an inorganic/organic semiconductor hybrid structure is experimentally observed. Time-resolved photoluminescence and excitation spectroscopy directly demonstrate that electronic excitation energy can be transferred with an efficiency of up to 50% from an inorganic ZnO quantum well to an organic [2,2-p-phenylenebis-(5-phenyloxazol), alpha-sexithiophene] overlayer. The coupling is mediated via dipole-dipole-interaction analog to the Förster transfer in donor-acceptor systems.

Laser action of trions in a semiconductor quantum well.

We report on the observation of optical gain and lasing at the trion transition of n-doped ZnSe quantum wells. Specifically, the (stimulated) emission-absorption net rate of this transition is controlled by the difference of trion and electron occupation in momentum space. As the mass of the trion is larger than that of the electron, gain occurs on the low-energy side of the line center without degeneracy and inversion in the total particle numbers. The scenario is reminiscent of a three-level system. At higher injection levels, carrier heating sets on and limits the available gain to values of about 10(4) cm(-1).

Investigation on molar mass, solubility and enzymatic fragmentation of xylans by multi-detected SEC chromatography.

Four xylan samples from different origin were investigated, using a multi-detector, size exclusion, chromatographic system with two chromatographic column sets and mobile phases differing in the DMSO:water ratio. Molar mass distribution could be analysed best using a mobile phase of DMSO:water (90:10) with addition of 0.05 M LiBr, a system offering good solubilisation of the polymers and a proper chromatographic separation. SEC analysis in aqueous systems provided information on solubility and aggregation of xylans. A comparison of UV- and RI-signals in different systems gave further information on lignin impurities, which in some cases were involved in aggregation phenomena. Both analytical systems were applied to study the enzymatic fragmentation of xylans. Combining the information derived from the two systems can differentiate between the enzymatic degradation of the well-dissolved and the associated polymer fractions.

Role of virulence factors, cell components and adhesion in Helicobacter pylori-mediated iNOS induction in murine macrophages.

To investigate the mechanisms involved in Helicobacter pylori-mediated inducible nitric oxide synthase (iNOS) upregulation in mononuclear cells we cocultivated human THP-1 acute monocytic leukemia cells and murine J774A.1 professional macrophages with different H. pylori wild-type strains and mutants. We have shown that H. pylori-mediated iNOS induction in J774A.1 is independent of established virulence factors but dependent on direct interaction between bacteria and cells. In J774A.1, iNOS was equally upregulated by the wild-type strains J99, 26695, P12, and P1 as well as by mutants lacking the cag pathogenicity island, vacA, katA, alpAB genes and the hp0043 gene taking part in lipopolysaccharide biosynthesis when direct cell contact was allowed but not when bacteria and cells were separated by protein-permeable filter membranes. In contrast, iNOS was not induced in THP-1. This indicates that H. pylori-mediated iNOS induction in J774A.1 is independent of important virulence factors whereas cell contact is crucial which suggests a role of adhesion or phagocytosis.

Interaction of Helicobacter pylori with professional phagocytes: role of the cag pathogenicity island and translocation, phosphorylation and processing of CagA.

Chronic infection of the human gastric mucosa with Helicobacter pylori is a major cause of gastroduodenal pathologies, including peptic ulcerations, mucosa-associated lymphoid tissue (MALT) lymphoma and adenocarcinoma. Helicobacter pylori strains carrying the cag pathogenicity island, which encodes an active type IV protein secretion system (cag+ or type I strains), are preferentially associated with strong gastric inflammation and severe disease. We show here that cag+ H. pylori strains use the type IV secretion system to inject the bacterial protein CagA into various types of professional phagocytes, including human polymorphonuclear leucocytes (PMNs) and the human and murine macrophage cell lines THP-1 and J774A.1 CagA is rapidly tyrosine phosphorylated and proteolytically processed to generate a stable 35-45 kDa C-terminally tyrosine-phosphorylated protein fragment. H. pylori was efficiently ingested by the different types of phagocytic cells. A chromosomal deletion of the complete pathogenicity island had no significant effect on the rate of ingestion. Furthermore, the survival rate of H. pylori in the phagosome was unchanged between the wild type and a deletion mutant lacking the type IV secretion system. Thus, the type IV secretion system seems to be involved neither in active phagocytosis resistance nor in prolonged survival of the bacteria in phagocytic cells.

Systematic mutagenesis of the Helicobacter pylori cag pathogenicity island: essential genes for CagA translocation in host cells and induction of interleukin-8.

Helicobacter pylori (Hp) carries a type IV secretion system encoded by the cag pathogenicity island (cag-PAI), which is used to: (i) translocate the bacterial effector protein CagA into different types of eukaryotic cells; and (ii) induce the synthesis and secretion of chemokines, such as interleukin-8 (IL-8). The cag-PAI in Hp 26695 consists of 27 putative genes, six of which were identified as homologues to the basic type IV secretion system represented by the Agrobacterium tumefaciens virB operon. To define the role and contribution of each of the 27 genes, we applied a precise deletion/insertion mutagenesis procedure to knock out each individual gene without causing polar effects on the expression of downstream genes. Seventeen out of 27 genes were found to be absolutely essential for translocation of CagA into host cells and 14 out of 27 for the ability of Hp fully to induce transcription of IL-8. The products of hp0524 (virD4 homologue), hp0526 and hp0540 are absolutely essential for the translocation of CagA, but not for the induction of IL-8. In contrast, the products of hp0520, hp0521, hp0534, hp0535, hp0536 and hp0543 are not necessary for either translocation of CagA or for IL-8 induction. Our data argue against a translocated IL-8-inducing effector protein encoded by the cag-PAI. We isolated a variant of Hp 26695, which spontaneously switched off its capacity for IL-8 induction and translocation of CagA, but retained the complete cag-PAI. We identified a point mutation in gene hp0532, causing a premature translational stop in the corresponding polypeptide chain, providing a putative explanation for the defect in the type IV secretion system of the spontaneous mutant.

Genetic competence in Helicobacter pylori: mechanisms and biological implications.

Helicobacter pylori is naturally competent for genetic transformation. The comB locus, consisting of the open reading frames orf2, comB1, comB2, and comB3, is involved in natural transformation competence. Homologies of the ComB proteins with components of the type IV secretion apparatus (VirB9 and VirB10) from the Ti plasmid of Agrobacterium tumefaciens, as well as proteins involved in conjugation of plasmids RP1 and RP4, suggest a similar organization of DNA import (transformation) in H. pylori with well-known DNA export systems.

Translocation of Helicobacter pylori CagA into gastric epithelial cells by type IV secretion.

The Gram-negative bacterium Helicobacter pylori is a causative agent of gastritis and peptic ulcer disease in humans. Strains producing the CagA antigen (cagA(+)) induce strong gastric inflammation and are strongly associated with gastric adenocarcinoma and MALT lymphoma. We show here that such strains translocate the bacterial protein CagA into gastric epithelial cells by a type IV secretion system, encoded by the cag pathogenicity island. CagA is tyrosine-phosphorylated and induces changes in the tyrosine phosphorylation state of distinct cellular proteins. Modulation of host cells by bacterial protein translocation adds a new dimension to the chronic Helicobacter infection with yet unknown consequences.

Hydrolysis of xylans by enzyme systems from solid cultures of Trichoderma harzianum strains.

Xylanase activity was isolated from crude extracts of Trichoderma harzianum strains C and 4 grown at 28 degree C in a solid medium containing wheat bran as the carbon source. Enzyme activity was demonstrable in the permeate after ultrafiltration of the crude extracts using an Amicon system. The hydrolysis patterns of different xylans and paper pulps by xylanase activity ranged from xylose, xylobiose and xylotriose to higher xylooligosaccharides. A purified ss-xylosidase from the Trichoderma harzianum strain released xylose, xylobiose and xylotriose from seaweed, deacetylated, oat spelt and birchwood xylans. The purified enzyme was not active against acetylated xylan and catalyzed the hydrolysis of xylooligosaccharides, including xylotriose, xylotetraose and xylopentaose. However, the enzyme was not able to degrade xylohexaose. Xylanase pretreatment was effective for hardwood kraft pulp bleaching. Hardwood kraft pulp bleached in the XEOP sequence had its kappa number reduced from 13.2 to 8.9 and a viscosity of 20. 45 cp. The efficiency of delignification was 33%.

Hydrolysis of xylans by enzyme systems from solid cultures of Trichoderma harzianum strains

Xylanase activity was isolated from crude extracts of Trichoderma harzianum strains C and 4 grown at 28oC in a solid medium containing wheat bran as the carbon source. Enzyme activity was demonstrable in the permeate after ultrafiltration of the crude extracts using an Amicon system. The hydrolysis patterns of different xylans and paper pulps by xylanase activity ranged from xylose, xylobiose and xylotriose to higher xylooligosaccharides. A purified ß-xylosidase from the Trichoderma harzianum strain released xylose, xylobiose and xylotriose from seaweed, deacetylated, oat spelt and birchwood xylans. The purified enzyme was not active against acetylated xylan and catalyzed the hydrolysis of xylooligosaccharides, including xylotriose, xylotetraose and xylopentaose. However, the enzyme was not able to degrade xylohexaose. Xylanase pretreatment was effective for hardwood kraft pulp bleaching. Hardwood kraft pulp bleached in the XEOP sequence had its kappa number reduced from 13.2 to 8.9 and a viscosity of 20.45 cp. The efficiency of delignification was 33

Purification and characterization of a low-molecular-weight xylanase produced by acrophialophora nainiana

A low-molecular-weight xylanase activity (XynI) was isolated from the fungus Acrophialophora nainiana after growth in a solid medium containing wheat bran. XynI was purified to apparent homogeneity by ultrafiltration and gel filtration chromatography. The purified enzyme had a molecular weight value of approx. 17 kDa, as determined by SDS-PAGE. This enzyme was most active at 50 degreesC and pH 6.0. At 50 degreesC the half-life was 150 min. The apparent Km value for birchwood xylan was much lower than the Km value for oat spelt xylan. XynI was activated by L-cysteine, DTE, beta-mercaptoethanol, and L-tryptophan. XynI did not show significant sequence homology with other xylanases. The analysis of hydrolysis products of xylans and wood pulps showed that XynI was able to release xylooligomers ranging from X2 to X3 and X2 to X6, respectively. The enzyme was not active against acetylated xylan. A small amount of xylose was released from deacetylated, birchwood, and oat spelt xylans. The results obtained with enzymatic treatment of Kraft pulp indicated a reduction in the amount of chlorine compounds required for the process and enhanced brightness gain.

Purification and characterization of two arabinofuranosidases from solid-state cultures of the fungus Penicillium capsulatum.

Two arabinofuranosidases, termed Ara I and Ara II, from solid-state cultures of Penicillium capsulatum were purified to apparent homogeneity as judged by electrophoresis and isoelectric focusing. Each enzyme is a single subunit glycoprotein, and they have M(r)s and pIs of 64,500 and 4.15 (Ara I) and 62,700 and 4.54 (Ara II), respectively. Ara I is most active at pH 4.0 and 60 degrees C, while Ara II exhibits optimal activity at pH 4.0 and 55 degrees C. Ara I is the more thermostable, with its half-life at 70 degrees C and pH 4.0 being 17.5 min. By contrast, the half-life of Ara II is only 9 min at 60 degrees C and pH 4.0. Ara I has the lower Km and higher catalytic constant values with p-nitrophenyl-alpha-L-arabinofuranoside being used as the substrate. Arabinose, a competitive inhibitor (Ki, 16.4 mM) of Ara II, has no effect on Ara I activity at concentrations of up to 40 mM. Each enzyme catalyzes the release of arabinose from pectin, araban, and certain arabinose-containing xylans. The last activity is enhanced by pretreatment of the relevant substrates with xylanase, ferulic acid esterase, or combinations of these enzymes. Thus, arabinoxylooligosaccharides in which arabinose is the sole side chain substituent appear to be the preferred substrates. On the basis of the evidence cited above, each enzyme has been classified as an alpha-L-arabinofuranoside arabinofuranohydrolase (EC 3.2.1.79).

Purification and Characterization of the (alpha)-Glucuronidase from Thermoanaerobacterium sp. Strain JW/SL-YS485, an Important Enzyme for the Utilization of Substituted Xylans.

A cell-associated (alpha)-glucuronidase was purified to gel electrophoretic homogeneity from the thermophilic anaerobic bacterium Thermoanaerobacterium sp. strain JW/SL-YS485. This enzyme had a pI of 4.65, a molecular weight of 130,000, and two subunits; the molecular weight of each subunit was 74,000. The enzyme exhibited the highest level of activity at pH 5.4 and 60(deg)C, as determined by a 5-min assay. The K(infm) and k(infcat) values of the enzyme for 4-methylglucuronosyl xylobiose were 0.76 mM and 1,083 IU/(mu)mol, respectively. The Arrhenius energy was 26.4 kJ/mol. The specific activities of the enzyme with 4-O-methylglucuronosyl xylobiose, 4-O-methylglucuronosyl xylotriose, and 4-O-methylglucuronosyl xylotetraose were 8.4, 4.8, and 3.9 IU/mg, respectively. The purified (alpha)-glucuronidase and a (beta)-xylosidase purified from the same organism interacted synergistically to hydrolyze 4-methylglucuronosyl xylotetraose.

Matrix isolation applied to the 252Cf plasma-desorption mass spectrometry of underivatized oligosaccharides.

A number of different low molecular weight and volatile compounds have been tested and compared as matrices in 252Cf plasma-desorption mass spectrometry (PDMS) measurements of oligosaccharides. Some heteroaromatic amines (2-aminothiazole and 3-aminopyridine), hydroxyanthraquinones (alizarin and quinalizarin) and phthaleins (fluorescein) proved to be especially suited to enhancing the quasimolecular ion intensity of oligosaccharides. Discrimination effects could be reduced by matrix addition and thus, quantitative results of PDMS could be improved. Oligosaccharides with broad molecular weight distribution (dextrin 10 and dextran T 1.5) have been successfully analyzed by PDMS. The mass spectra obtained compared quite well with ion chromatograms of the respective oligosaccharides.