Siderophore-Mediated microbial iron(III) uptake: An exercise in chiral recognition

Molecular recognition by microbial receptors for siderophores [natural iron(III) carriers] is examined with synthetic iron(III) carriers as structural probes. The iron(III) carriers have been designed to reproduce the two essential features of the natural siderophores: the capability to form octahedral iron(III) binding cavities and to fit specific membrane receptors. Specifically, analogs of tripodal ferrichrome and linear ferrioxamines have been prepared and examined. The ferrichrome analogs rely on C₃-symmetric binders that are assembled from triscarboxylates as anchors, amino acids as bridges, and terminal hydroxamate groups as binding sites. The ferrioxamine analogs are based on linear assemblies of three identical monomers, each derived from a chiral amino acid. The deliberate use of animo acid residues as variable building blocks enables us to systematically modify the molecules' envelopes and the preferred absolute configuration of the iron(III) complexes until optimal performance is reached. Examination of the synthetic analogs in Pseudomonas putida demonstrates that the domains around the iron(III) center and their chiral sense dictate the extent of recognition by the membrane receptors. It is also shown that the synthetic siderophore analogs may be designed to either exert a broader, or a more narrow range of microbial activity than the natural siderophores. The implications of these findings are discussed in relation to the possible design of species-specific antimicrobial agents. © 1993 Wiley-Liss, Inc.     

Build-up and decline ofRhizoctonia solani inoculum under field conditions

Summary Inoculum potential ofRhizoctonia solani Kühn was studied in an infested carnation field during two successive growth seasons. This inoculum potential was expressed as diseased carnation plants in the field and diseased bean seedlings planted in soil samples. Disease incidence in the field soil samples increased during the first season, up to 60% and 100%, respectively. Removing the carnation plants and keeping the soil wet for 45 days, resulted in a sharp decline in inoculum potential. Both inoculum potential and disease incidence in carnations were lower after plant removal. The use of either methyl bromide or vapam resulted in complete control of the disease and reduced inoculum potential. Results suggest possible reduction ofR. solani inoculum by maintaining the soil moist between growth periods.     

Effects of L-tryptophan on morphogenesis and growth in the early chick blastoderm

Summary Chick blastoderms, suppliedin vitro andin ovo with L-tryptophan at the primitive streak stage, showed in their continued development typical retardation of brain formation and somitogenesis in the embryo, whereas heart formation remained unaffected. In contrast to an overall reduction in size observed at the higher L-tryptophan concentrations, a moderate enlargement of the area opaca, compared with the controls, was found at the lower concentrations. This enlargement was combined with an increased flattening of the ectodermal area opaca cells and a reduction of the number of microvilli covering these cells. As a simultaneous supply of glucose could reduce, to some extent, the morphogenetic disturbances, these might partly be ascribed to a blocking of gluconeogenesis from L-tryptophan, but the overall reduction in size mentioned, together with the observation of a reduced decomposition of intracellular yolk granules in the L-tryptophan-treated blastoderms, indicates that impairment of intracellular yolk granule decomposition was the principal disturbance. The possible role of serotonin—probably formed from the L-tryptophan supplied—is suggested as a regulating factor in this connexion.     

Differential Siderophore Utilization and Iron Uptake by Soil and Rhizosphere Bacteria

The differential availabilities of the hydroxamate siderophores ferrioxamine B (FOB) and ferrichrome (FC) and the pseudobactin siderophores St3, 7NSK₂, and WCS 358 as sources of Fe for soil and rhizosphere bacteria were studied. About 20% of the total bacterial CFU from the rhizospheres of four plant species were able to use FOB as the sole Fe source in an Fe-deficient medium, while about 12, 10, 2, and > 1% were able to use FC and pseudobactins 7NSK₂, St3, and WCS 358, respectively. Of the 165 colonies isolated from plates containing pseudobactins, 64 were able to use the pseudobactin on which they were isolated as the sole Fe source in pure culture. Cross-feeding tests showed that almost all of these 64 strains were also able to use at least one of the other siderophores studied (pseudobactin, FOB, or FC). Pseudomonas putida StS2, Pseudomonas maltophilia 7NM1, and Vibrio fluvialis WS1, which were originally isolated on pseudobactins St3, 7NSK₂, and WCS 358, respectively, were selected for their ability to grow with pseudobactin St3 as the sole Fe source. They incorporated ⁵⁵Fe³⁺ mediated by pseudobactin St3 at various rates (71.5, 4, and 23 pmol/min/mg [dry weight] of cells, respectively). Similarly, P. putida St3 was shown to incorporate ⁵⁵Fe³⁺ mediated by FOB and FC. We suggest that the ability of bacteria to utilize a large variety of siderophores confers an ecological advantage.     

Utilization of lignocellulosic waste by the edible mushroom,Pleurotus

Lignocellulosic waste represents huge amounts of unutilized renewable resource. The use of the polysaccharides in the lignocellulosic complex is limited due to their high lignin content. White rot fungi are capable of selectively degrading lignin, thereby upgrading it. The focus of this article is on the potential utilization of edible mushrooms of the genus Pleurotus, via solid state fermentation, using cotton plant stalks as a substrate. This material poses agrotechnical problems since the stalks have a fibrous structure similar to that of hardwood. Potential uses for this material are as a fuel in rural areas, a substrate for mushrooms, an animal feed and substrate for paper making. In this study, degradation of cotton stalks by Pleurotus is described using chemical analyses and scanning electron microscopy. During four weeks of solid state fermentation, lignin content significantly decreased and in vitro digestibility was increased. The fermentation product was consumed by ruminants at a level of up to 40% of their diet.     

Possible involvement of putrescine in nucleolar formation in early embryos

Summary Continuous treatment of developing eggs of the polychete Ophryotrocha labronica with -methylornithine, which inhibits synthesis of putrescine, led to arrest of development at gastrulation. The present ultrastructural analysis suggests that the arrest of development is due to failure to form nuclei, and thus reveals a possible role for putrescine in nucleolar formation. Further support for this contention was provided by means of electron-microscopical autoradiography. It was found that newly synthesized putrescine, derived from administered ³H-ornithine, labeled the nucleoli intensely at the time of their normal appearance during gastrulation, the time at which the rate of endogenous putrescine synthesis is maximal. These observations have led to the conclusion that putrescine synthesis may be directly involved in formation of nucleoli.We thank Mrs Lena Olsson and Mrs Annagreta Petersen for excellent technical assistance. This investigation was supported by the Swedish Natural Science Research Council     

A facile and effective synthesis of dinucleotide 5'-triphosphates

We report on the successful synthetic procedure for the conversion of 5'-monophosphorylated 2'-deoxydinucleotides into their 5'-triphosphate derivatives in satisfactory to excellent yields. The activation of the terminal phosphate group was achieved under the Mukaiyama conditions in the presence of a nucleophilic catalyst. The reaction conditions (solvent, counter ions, activation time and reagent excess) were optimized for all dinucleotides.     

Breakdown of Inter-Hemispheric Connectivity Is Associated with Posttraumatic Symptomatology and Memory Impairment

Altered brain anatomy in specific gray-matter regions has been shown in patients with posttraumatic stress disorder (PTSD). Recently, white-matter tracts have become a focus of research in PTSD. The corpus callosum (CC) is the principal white-matter fiber bundle, crucial in relaying sensory, motor and cognitive information between hemispheres. Alterations in CC fibers have been reported in PTSD and might be assumed to underlie substantial behavioral and cognitive sequelae; however most diffusion tensor imaging (DTI) studies in adult-onset PTSD failed to address the clinical correlates between imaging and PTSD symptoms severity, behavioral manifestation and cognitive functions. In the current study we examined (a) to what extent microstructural integrity of the CC is associated with memory performance and (b) whether imaging and cognitive parameters are associated with PTSD symptom severity. DTI data were obtained and fractional anisotropy (FA) values were computed for 16 patients and 14 controls. PTSD symptom severity was assessed by employing the clinician administered PTSD scale (CAPS) and memory was tested using a task probing item and associative memory for words and pictures. Significant correlations were found between PTSD symptoms severity, memory accuracy and reaction-time to CC FA values in the PTSD group. This study demonstrates meaningful clinical and cognitive correlates of microstructural connectivity. These results have implications for diagnostic tools and future studies aimed at identifying individuals at risk for PTSD.     

Chemical characterization, antiproliferative and antiadhesive properties of polysaccharides extracted from Pleurotus pulmonarius mycelium and fruiting bodies

Mushroom polysaccharides are potent substances that exhibit antitumor and immunomodulatory properties. Studies comparing the chemical composition and antitumor-related activities of polysaccharides released by fungal strains under different growth conditions are not available. Thus, the present study compared polysaccharides extracts produced by Pleurotus pulmonarius from mycelium grown in liquid culture (ME) or fruiting bodies (FBE). Polysaccharides of both ME and FBE had a relatively high molecular mass. NMR spectroscopy indicated that ME glucan is an α-glucan whereas FBE glucan is a mixture of both α- and β-glucans. Glucose and galactose where the most prominent monosaccharide in both glucans. Treatment of several colon cancer cell lines expressing varying amounts of galectin-3 with the two fungal glucans inhibited their viability and significantly reduced their ability to adhere to the key component of the extracellular matrix, fibronectin, and to a human umbilical vein endothelial cell monolayer, in a time- and dose-dependent manner mainly in those cell lines expressing high amounts of galectin-3. We conclude that ME and FBE glucans may exert a direct antiproliferative effect on cancer cells expressing high galectin-3 concentrations and concomitantly downregulate tumor cell adherence, the latter being directly related to cancer progression and metastasis.