A taxonomic study of Salix section Cordatae subsection Luteae (Salicaceae)

Salix sectionCordatae subsectionLuteae includes 10 taxa and occurs in most of North America. The taxa are here treated as four species, one with six varieties and another with two varieties. Six new combinations are proposed underSalix eriocephala.     

Anti-pathogenic Potential of Coral Associated Bacteria Isolated from Gulf of Mannar Against Pseudomonas aeruginosa

Infections of Pseudomonas aeruginosa are of great concern because of its increasing resistance towards conventional antibiotics. Quorum sensing system of P. aeruginosa acts as a global regulator of almost all the virulence factors and majorly its biofilm formation. In the present study, quenching of QS system of P. aeruginosa has been explained with bioactives from bacteria associated with the coral Acropora digitifera. Isolated bioactives inhibited the expression of various virulence traits of P. aeruginosa like biofilm formation, and the production of extracellular enzymes like protease and elastase. This study also emphasises the potential of coral associated bacteria in producing bioactive agents with anti-pathogenic properties.     

Pathogenic fungal dynamics in a fall population of the blackmargined aphid (Monellia caryella)

A fall population of the blackmargined aphid, Monellia caryella (Fitch) (Homoptera: Aphididae), was monitored daily for mortality caused by fungi and parasitoids. Three species of Entomophthorales fungi were found. Fungal-induced mortality was found to be correlated with minimum temperature. During the period when the minimum temperature was consistently above 8°C, fungal-induced mortality was positively correlated with the sum of hours of leaf-wetness on days 5, 6, and 7 before sampling. Parasitoid wasps killed fewer hosts than fungi and were not affected by environmental factors.

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Résumé La mortalité quotidienne provoquée par des parasitoïdes et des champignons sur une population automnale de M. caryella Fitch (Homopt. Aphididae) a été suivie à Byron (Géorgie, USA), avec enregistrement de la température, de la pluie et de l'humidité des feuilles. 3 espèces de champignons entomophthorales ont été trouvées: Neozygites sp., Entomophthora planchoniana et Erynia sp. 54% des pucerons morts étaient contaminés par Neozygites et 46% par E. planchoniana. Seuls 2 pucerons avaient été tués par Erynia sp. Les taux de mortalité quotidienne par champignons s'élevaient après les périodes pluvieuses et d'humidité des feuilles. La mortalité due au parasitisme était inférieure à la mortalité due aux champignons et ne semblait pas liée aux conditions écologiques. La discussion porte sur l'importance de la mortalité provoquée par les champignons sur la dynamique de la population de pucerons.

     

Experimental Exposures of Boreal Toads (Bufo boreas) to a Pathogenic Chytrid Fungus (Batrachochytrium dendrobatidis)

One of the major causes of worldwide amphibian declines is a skin infection caused by a pathogenic chytrid fungus (Batrachochytrium dendrobatidis). This study documents the interactions between this pathogen and a susceptible amphibian host, the boreal toad (Bufo boreas). The amount of time following exposure until death is influenced by the dosage of infectious zoospores, duration of exposure, and body size of the toad. The significant relation between dosage and the number of days survived (dose-response curve) supports the hypothesis that the degree of infection must reach a particular threshold of about 10⁷–10⁸ zoosporangia before death results. Variation in air temperature between 12°C and 23°C had no significant effect on survival time. The infection can be transmitted from infected to healthy animals by contact with water containing zoospores; no physical contact between animals is required. These results are correlated with observations on the population biology of boreal toads in which mortalities associated with B. dendrobatidis have been identified.     

Presence of myelin-like structures in tanniferous vascular parenchyma cells ofSalix dasyclados Wim.

Summary In the cambial region ofSalix dasyclados plants, extensive spherical formations of myelin-like lamellar configurations were found during the transit period between winter dormancy and reactivation of growth in early spring. The lamellar structures occurred in parenchyma cells containing tannins and were associated with spherosomes. Cytomembranes in tannin-containing cells appeared with negative contrast on electron micrographs, indicating the presence of tanniferous substances in the cytoplasm.Abbreviation R_G relative growth rate (% fresh weight increase per day)     

Presence and behaviour of B-chromosomes in Acanthophyllum laxiusculum (Caryophyllaceae)

Two karyotypic variants were recognized in populations of Acanthophyllum laxiusculum Schiman-Czeika. Variant A had 2N = 30 and variant B showed the presence of 0 to 3 B-chromosomes in addition to 2N = 30 chromosomes. Analysis of chromosome behaviour at meiosis showed that the presence of B-chromosomes increases chiasma frequency in A-chromosomes; this effect was higher for plants with odd numbers of B-chromosomes compared with plants with even numbers of B-chromosomes. Comparisons of variants A and B, suggests that B-chromosomes have an effect pollen stainability and seed production. It seems that the presence of B-chromosomes may increase pollen stainability and seed production in variant B.     

Pathogenic potential of six isolates of entomopathogenic nematodes (Rhabditida: Steinernematidae) from Vietnam

The potential of six Steinernema isolates, isolated from different provinces in Vietnam, was evaluated in the laboratory against Galleria mellonella and Spodoptera littoralis. Steinernema sangi and S. robustispiculum TN24 had the highest penetration rate in both hosts according to a penetration rate assay. The virulence assay showed that S. sangi had a high virulence to both hosts and along with isolate TN38 it was the most mobile among the isolates tested. The migration of S. sangi in sand columns with an insect host at the bottom was significantly higher than in sand columns without insect host. This Steinernema species was the only one that penetrated a host in 24h after migrating 10cm in sand columns at 25°C. Moreover, a multiplication assay showed that S. sangi produced a high number of infective juveniles in G. mellonella. However, all Steinernema isolates tested had low multiplication rates in S. littoralis.     

Regulation of CaCO(3) formation in coccolithophores

Coccolithophores impact the ocean carbon cycle principally through the generation of CO₂ during CaCO₃ production. Coccolithophore biomineralization has been examined most extensively in Pleurochrysis carterae and Emiliania huxleyi both of which produce mineralized scales—coccoliths—composed of elaborate calcite crystals attached to an underlying organic base plate. Calcification of preformed base plates is mediated by acidic polysaccharides and occurs in Golgi-derived structures known as mineralizing vesicles. In Pleurochrysis a high capacity calcium-binding polysaccharide PS2 is required for efficient nucleation of calcitic protocrystals. A galacturonomannan PS3 is required for the growth and transformation of the protocrystals into a massive double disc of calcite. The genes that regulate expression of the glycans have not yet been identified. In addition to the coccolith-bearing diploid phases, Pleurochrysis and Emiliania possess both haploid and diploid non-calcifying stages, which are self-perpetuating via binary fission. One non-calcifying Pleurochrysis phase fails to synthesis PS2 and spontaneously reverts to the mineralizing morphotype in laboratory cultures. As yet, there is little information on environmental factors that effect the expression or silencing of calcifying genes or favor the growth of calcifying over non-calcifying phases. These issues will need extensive investigation, if we are to appreciate the role of coccolithophores in the regulation of atmospheric CO₂ levels.     

Presence of sporangia of Frankia in the rhizosphere of Discaria (Rhamnaceae)

Discaria trinervis and Discaria americana are native actinorhizal plants in Argentina. Discaria seedlings growing in N-free liquid culture, inoculated with dry soils, developed Frankia colonies in the rhizosphere. The occurrence of hyphae, vesicles and sporangia characteristic of Frankia are described in these colonies. The presence of sporangia of Frankia has previously neither been reported in the genus Discaria, nor in the other genera of the tribe Colletieae inside root nodules or outside roots. The infective capacity of the colonies has been demonstrated.     

Inhibition of <Emphasis Type="Italic">Vibrio</Emphasis> biofilm formation by a marine actinomycete strain A66

China remains by far the largest aquaculture producer in the world. However, biofilms formed by pathogenic Vibrio strains pose serious problems to marine aquaculture. To provide a strategy for biofilm prevention, control, and eradication, extracts from 88 marine actinomycetes were screened. Thirty-five inhibited the biofilm formation of Vibrio harveyi, Vibrio vulnificus, and Vibrio anguillarum at a concentration of 2.5% (v/v). Thirty-three of the actinomycete extracts dispersed the mature biofilm. Six extracts inhibited the quorum-sensing system of V. harveyi by attenuating the signal molecules N-acylated homoserine lactones’ activity. Strain A66, which was identified as Steptomyces albus, both attenuated the biofilms and inhibited their quorum-sensing system. It is suggested that strain A66 is a promising candidate to be used in future marine aquaculture.     

The Presence of Actinidin (Cysteine Protease) and Recombinant Plasmids Carrying the Actinidin Gene Influence the Growth of Saccharomyces Cerevisiae

Actinidin is a protease found abundantly in the fruit of Actinidia chinensis or Kiwi fruit. The overproduction of this protein in microorganisms, especially using the yeast Saccharomyces cerevisiae, would be economically valuable as it would simplify the extraction and purification of the protein. It was observed, however, that the yeast growth rate was reduced by the presence of externally supplied actinidin in the growth medium. It was also observed that actinidin present in the yeast growth medium was partially degraded. Several actinidin-encoding gene variants have been cloned in a yeast expression and secretion vector. It was observed that different actinidin gene constructions influenced the growth rate of S. cerevisiae in complete media. Recombinant plasmids carrying only the mature actinidin-encoding DNA sequences reduced yeast transformability significantly and had the least stability. The results thus suggest that the presence of a recombinant plasmid carrying a gene of a potentially toxic protein may result in a deleterious effect on the host cell.     

Indole Affects Biofilm Formation in Bacteria

Biofilm is bacterial population adherent to each other and to surfaces or interfaces, often enclosed by a matrix. Various biomolecules contribute to the establishment of biofilms, yet the process of building a biofilm is still under active investigation. Indole is known as a metabolite of amino acid tryptophan, which, however, has recently been proved to participate in various aspects of bacterial life including virulence induction, cell cycle regulation, acid resistance, and especially, signaling biofilm formation. Moreover, indole is also proposed to be a novel signal involved in quorum sensing, a bacterial cooperation behavior sometimes concerning the biofilm formation. Here the signaling role and molecular mechanism of indole on bacterial biofilm formation are reviewed, as well discussed is its relation to bacterial living adaptivity.     

Gene flow inAgrostis tenuis (Poaceae)

The copper tolerance of both adult plants and their seedlings, ofAgrostis tenuis from sites within and outside, but neighbouring the Parys Mountain mine (North Wales) were studied. Intensive sampling was carried out along a line starting from the mine boundaries to a distance of five miles away in the direction of the prevailing wind, and of two miles in an upwind direction. The test have shown that mine populations are very tolerant. In outside populations on soils with reduced of very low copper content the mean tolerance level of the seedlings is considerably higher than that of corresponding adult plants, while both show a gradual decrease in tolerance with distance from the mine. The gene flow moves in the direction of the prevailing wind transfering tolerant characters from the mine to the normal populations. The selective pressures on the toxic soil of the mine are quite strong and permit ± tolerant plants only, while on normal soils these pressures are not so severe, so that populations may be rather heterogenous regarding their tolerance towards copper.     

Pseudomonas aeruginosa quorum sensing molecule N-(3 oxododecanoyl)-l-homoserine lactone disrupts epithelial barrier integrity of Caco-2 cells

Acyl-homoserine lactone (HSL) quorum sensing molecules play an important role in regulation of virulence gene expression in Pseudomonas aeruginosa. Here, we show that 3O-C(12)-HSL can disrupt barrier integrity in human epithelial Caco-2 cells as evidenced by decreased transepithelial electrical resistance (TER), increased paracellular flux, reduction in the expression and distribution of ZO-1 and occludin, and reorganization of F-actin. P. aeruginosa 3O-C(12)-HSL activate p38 and p42/44 kinases, and inhibition of these kinases partly prevented 3O-C(12)-HSL-induced changes in TER, paracellular flux and expression of occludin and ZO-1. These findings demonstrate that P. aeruginosa 3O-C(12)-HSL can modulate tight junction integrity of Caco-2 cells.     

<Emphasis Type="Italic">N</Emphasis>-acyl homoserine lactones are degraded via an amidolytic activity in <Emphasis Type="Italic">Comamonas</Emphasis> sp. strain D1

Abtsract Comamonas strain D1 enzymatically inactivates quorum-sensing (QS) signal molecules of the N-acyl homoserine lactone (N-AHSL) family, and exhibits the broadest inactivation range of known bacteria. It degrades N-AHSL with acyl-side chains ranging from 4 to 16 carbons, with or without 3-oxo or 3-hydroxy substitutions. N-AHSL degradation yields HSL but not N-acyl homoserine: strain D1 therefore harbors an amidohydrolase activity. Strain D1 is the fifth bacterium species in which an N-AHSL amidohydrolase is described. Consistent with its N-AHSL degradation ability, strain D1 efficiently quenches various QS-dependent functions in other bacteria, such as violacein production by Chromobacterium violaceum and pathogenicity and antibiotic production in Pectobacterium.     

Components of resistance of leaf rust (Melamspora laricii epitea Kleb./Melampsora ribesii-viminalis Kleb.) in Salix viminalis L.

Selection on partial resistance components, namely latent period, development rate of uredia and number and size of uredia, has been suggested as a means to achieve durable resistance. Three experiments were carried out in growth chambers to assess the impact of environmental and genetic factors on these components in the Salix-Melampsora host-pathogen system. They confirmed the environmental ability of the Melampsora-Salicaceae relationship and provided no definite answer on the possibility of attaining durable resistance through selection on partial resistance components. On the one hand, there is a large amount of heritable variation among clones for most components; on the other hand, all components were extremely sensitive to environmental conditions and isolates, making the development of standard selection methods difficult.