Frequency-resolved intramolecular excimer fluorescence study of lipid bilayer and nonbilayer phases

Frequency-domain fluorescence intensity decays of the intramolecular excimer forming (DipyPE) in a fully hydrated dioleoyl-phosphatidylethanolamine (DOPE) suspension have been measured at the monomer (395 nm) and excimer (475 nm) emissions and at different temperatures (0-30°C). A classical Birks (two-state) and a new three-state kinetics models were used to analyze the frequency-domain data. The three-state model allowed us to resolve various intramolecular dynamics parameters of DipyPE in the host DOPE suspension. Those parameters are the excimer association (K_dm) and dissociation (K_md) rate constants, effective concentration (C), and lateral diffusion rate (f) of the pyrene moieties in the DipyPE. In contrast, only CK_dm and K_md were determined based on the two-state model. We observed that K_dm declined while C increased abruptly at ∼12°C, the known thermotropic lamellar liquid crystalline-to-inverted hexagonal (L_α-H_II) phase transition temperature of DOPE. No abrupt changes in K_md and f were observed at all temperatures. We concluded that the rotation of the lipid acyl chains is hindered and the free volume available for the lipid terminal methyl ends is reduced as the lipid membrane enters the highly curved H_II phase from the planar L_α phase.     

Molecular Detection and Pathogenicity Assay of Plasmodiophora brassicae in Chicken Manure

To determine the relationship between animal excreta and the occurrence of clubroot disease of cruciferous crops caused by Plasmodiophora brassicae, chickens were fed with resting spores of the pathogen. Their faeces were collected and used to inoculate crucifers. This study proved that both fresh and composted manures could induce clubroot and the presence of the pathogen in the manure was confirmed by PCR amplification. However, composting had detrimental effects on the virulence of the resting spores in the manure. When the temperature was over 32°C, the incidence and severity of clubroot declined with the increase in the exposure time of resting spores to high temperature and the pathogenicity was completely lost when the spores were kept at 48°C for 6 h. The control measures for the clubroot disease were discussed.     

Flexibility and ligand exchange in a buried cavity mutant of T4 lysozyme studied by multinuclear NMR

The Leu99-->Ala mutant of T4 lysozyme contains a large internal cavity in the core of its C-terminal domain that is capable of reversibly binding small hydrophobic compounds. Although the cavity is completely buried, molecules such as benzene or xenon can exchange rapidly in and out. The dynamics of the unliganded protein have been compared to the wild-type protein by measuring the NMR spin relaxation rates of backbone amide and side chain methyl nuclei. Many residues surrounding the cavity were found to be affected by a chemical exchange process with a rate of 1500 +/- 200 s(-1), which is quenched upon addition of saturating amounts of the ligand xenon. The relationship between the structure, dynamics, and energetics of the T4 lysozyme mutant is discussed.     

Parity and age composition for Anopheles darlingi root (Diptera: Culicidae) and Anopheles albitarsis Lynch-Arribálzaga (Diptera: Culicidae) of the northern Amazon Basin, Brazil.

Parity and age composition for Anopheles darlingi and Anopheles albitarsis in the northern Amazon Basin, Brazil, were investigated. Anopheline ovaries and ovarioles were examined in order to determine whether hourly and seasonal parity status for the vectors An. albitarsis and An. darlingi would vary in two different landscapes (forest and savanna/forest) where malaria is endemic in the northern Amazon Basin. A total of 1,199 anophelines (535 An. darlingi and 664 An. albitarsis) was dissected for parity status, ovariole dilatations, and follicular stages. The total number of nulliparous and parous females for both species varied by time of collection, locality, and season. During the rainy season for the first two h of collection, more nulliparous An. albitarsis and An. darlingi females were collected in the first hour (18:00-19:00), but during the second hour (19:00-20:00) more parous females of both species were captured. During the dry season in Copaíbas, more parous females of An. albitarsis were observed in the first hour while more nulliparous females were observed in the second hour. Nulliparous and parous females of both species for both hours were not significantly different at Road 19 in the dry season. This location was characterized by a forest malaria pattern of transmission with higher numbers of parous females and population stability in the dry season. In Copaíbas, the density and parity of An. darlingi increased during the rainy season, and it could be classified as an alluvial malaria pattern of transmission. For Copaíbas, control measures would be more successful if adopted at the transition from dry to rainy season. Further investigation on longitudinal spatio-temporal change in longevity and survival rates would help us to clarify differences in vector competence for An. darlingi and An. albitarsis and add to the understanding of differences regarding prevailing landscapes in malaria epidemiology in the northern Amazon Basin.     

Characterization of low-pathogenicity H5N1 avian influenza viruses from North America

Wild-bird surveillance in North America for avian influenza (AI) viruses with a goal of early identification of the Asian H5N1 highly pathogenic AI virus has identified at least six low-pathogenicity H5N1 AI viruses between 2004 and 2006. The hemagglutinin (HA) and neuraminidase (NA) genes from all 6 H5N1 viruses and an additional 38 North American wild-bird-origin H5 subtype and 28 N1 subtype viruses were sequenced and compared with sequences available in GenBank by phylogenetic analysis. Both HA and NA were phylogenetically distinct from those for viruses from outside of North America and from those for viruses recovered from mammals. Four of the H5N1 AI viruses were characterized as low pathogenicity by standard in vivo pathotyping tests. One of the H5N1 viruses, A/MuteSwan/MI/451072-2/06, was shown to replicate to low titers in chickens, turkeys, and ducks. However, transmission of A/MuteSwan/MI/451072-2/06 was more efficient among ducks than among chickens or turkeys based on virus shed. The 50% chicken infectious dose for A/MuteSwan/MI/451072-2/06 and three other wild-waterfowl-origin H5 viruses were also determined and were between 10(5.3) and 10(7.5) 50% egg infective doses. Finally, seven H5 viruses representing different phylogenetic clades were evaluated for their antigenic relatedness by hemagglutination inhibition assay, showing that the antigenic relatedness was largely associated with geographic origin. Overall, the data support the conclusion that North American H5 wild-bird-origin AI viruses are low-pathogenicity wild-bird-adapted viruses and are antigenically and genetically distinct from the highly pathogenic Asian H5N1 virus lineage.     

Silica Nanohybrid Membranes with High CO2 Affinity for Green Hydrogen Purification

An effective separation of CO₂ from H₂ can be achieved using currently known polyethylene oxide (PEO)‐based membranes at low temperatures but the CO₂ permeability is inadequate for commerical operations. For commercial‐scale CO₂/H₂ separation, CO₂ permeability of these membranes must be significantly enhanced without compromising CO₂/H₂ selectivity. We report here exceptional CO₂/H₂ separation properties of a nanohybrid membrane comprising polyethylene glycol methacrylate (PEGMA) grafts on an organic‐inorganic membrane (OIM) consisting of a low molecular weight polypropylene oxide (PPO)‐PEO‐PPO diamine and 3‐glycidyloxypropyltrimethoxysilane (GOTMS), an alkoxysilane. The CO₂ gas permeability of this nanohybrid membrane can reach 1990 Barrer with a CO₂/H₂ selectivity of 11 at 35 °C for a mixed gas mixture comprising 50% CO₂ ‐ 50% H₂ at 3.5 atm. The transformation of the inorganic silica phase from a well‐dispersed network of finely defined nanoparticles to rough porous clusters appears to be responsible for this OIM membrane exceeding the performance of other state‐of‐the‐art PEO‐based membranes.     

Time-resolved fluorescence and fourier transform infrared spectroscopic investigations of lateral packing defects and superlattice domains in compositionally uniform cholesterol/phosphatidylcholine bilayers

Time-resolved fluorescence and Fourier transform infrared spectroscopies were used to investigate the lateral organization of lipids in compositionally uniform and fully equilibrated 1-palmitoyl-2-oleoyl-phosphatidylcholine/cholesterol (POPC/CHOL) liposomes prepared by a recently devised low-temperature trapping method. Independent fluorescence decay lifetime and rotational dynamics parameters of diphenylhexatriene (DPH) chain-labeled phosphatidylcholine (DPH-PC) in these liposomes were recovered from the time-resolved fluorescence measurements as a function of cholesterol molar fraction (X(CHOL)) at 23 degrees C. The results indicate significantly greater lifetime heterogeneity, shorter average lifetime, rotational correlation time, and lower order parameter of the DPH moiety at X(CHOL) approximately 0.40 and 0.50 as compared to the adjacent cholesterol concentrations. Less prominent changes were also detected at, for example, X(CHOL) approximately 0.20 and 0.33. These X(CHOL)'s coincide with the "critical" X(CHOL)'s predicted by the previously proposed superlattice (SL) model, thus indicating that POPC and cholesterol molecules tend to form SL domains where the components tend to be regularly distributed. The data also support another prediction of the SL model, namely that lateral packing defects coexist with the ordered SL domains. It appears that unfavorable interaction of the DPH-moiety of DPH-PC with cholesterol results in a preferential partition of DPH-PC to the defect regions. Fourier transform infrared analysis of the native lipid O=P=O, C=O, and C-H vibrational bands of POPC/CHOL liposomes in the absence of DPH-PC revealed an increase in the conformational order of the acyl chains and a decrease in the conformational order (or increased hydration) of the interfacial and headgroup regions at or close to the predicted critical X(CHOL)'s. This provides additional but probe-independent evidence for SL domain formations in the POPC/CHOL bilayers. We propose that the defect regions surrounding the putative SL domains could play an important role in modulating the activity of various membrane-associated enzymes, e.g., those regulating the lipid compositions of cell membranes.     

Actinomyces hongkongensis sp. nov. a novel Actinomyces species isolated from a patient with pelvic actinomycosis

A bacterium was isolated from the pus of a patient with pelvic actinomycosis. The cells were strictly anaerobic, straight, non-sporulating, Gram-positive rods. It grows on sheep blood agar as non-haemolytic, pinpoint colonies after 24 hours of incubation at 37 degrees C in anaerobic environment. It is non-motile and does not produce catalase. 16S ribosomal RNA (rRNA) gene sequencing showed that there were 6.6% difference between the 16S rRNA gene sequence of the bacterium that of Actinomyces marimammalium (GenBank Accession no. AJ276405), a new species described in 2001, isolated from two seals and a porpoise. For these reasons a new species, Actinomyces hongkongensis sp. nov., is proposed, for which HKU8(T) is the type strain. Further studies should be performed to ascertain the potential of this bacterium to become an important cause of actinomycosis.     

Induction of Defense-Related Responses in Cf9 Tomato Cells by the AVR9 Elicitor Peptide of Cladosporium fulvum Is Developmentally Regulated

The AVR9 elicitor from the fungal pathogen Cladosporium fulvum induces defense-related responses, including cell death, specifically in tomato (Lycopersicon esculentum Mill.) plants that carry the Cf-9 resistance gene. To study biochemical mechanisms of resistance in detail, suspension cultures of tomato cells that carry the Cf-9 resistance gene were initiated. Treatment of cells with various elicitors, except AVR9, induced an oxidative burst, ion fluxes, and expression of defense-related genes. Agrobacterium tumefaciens-mediated transformation of Cf9 tomato leaf discs with Avr9-containing constructs resulted efficiently in transgenic callus formation. Although transgenic callus tissue showed normal regeneration capacity, transgenic plants expressing both the Cf-9 and the Avr9 genes were never obtained. Transgenic F₁ seedlings that were generated from crosses between tomato plants expressing the Avr9 gene and wild-type Cf9 plants died within a few weeks. However, callus cultures that were initiated on cotyledons from these seedlings could be maintained for at least 3 months and developed similarly to callus cultures that contained only the Cf-9 or the Avr9 gene. It is concluded, therefore, that induction of defense responses in Cf9 tomato cells by the AVR9 elicitor is developmentally regulated and is absent in callus tissue and cell-suspension cultures, which consists of undifferentiated cells. These results are significant for the use of suspension-cultured cells to investigate signal transduction cascades.