N-octane diffusivity enhancement via carbon dioxide in silica slit-shaped nanopores – a molecular dynamics simulation

Equilibrium molecular dynamics simulations were conducted to study the competitive adsorption and diffusion of mixtures containing n-octane and carbon dioxide confined in slit-shaped silica pores of width 1.9 nm. Atomic density profiles substantiate strong interactions between CO₂ molecules and the protonated pore walls. Non-monotonic change in n-octane self-diffusion coefficients as a function of CO₂ loading was observed. CO₂ preferential adsorption to the pore surface is likely to attenuate the surface adsorption of n-octane, lower the activation energy for n-octane diffusivity, and consequently enhance n-octane mobility at low CO₂ loading. This observation was confirmed by conducting test simulations for pure n-octane confined in narrower pores. At high CO₂ loading, n-octane diffusivity is hindered by molecular crowding. Thus, n-octane diffusivity displays a maximum. In contrast, within the concentration range considered here, the self-diffusion coefficient predicted for CO₂ exhibits a monotonic increase with loading, which is attributed to a combination of effects including the saturation of the adsorption capacity of the silica surface. Test simulations suggest that the results are strongly dependent on the pore morphology, and in particular on the presence of edges that can preferentially adsorb CO₂ molecules and therefore affect the distribution of these molecules equally on the pore surface, which appears to be required to provide the effective enhancement of n-octane diffusivity.     

Methadone Maintenance Treatment Promotes Referral and Uptake of HIV Testing and Counselling Services amongst Drug Users and Their Partners

BackgroundMethadone maintenance treatment (MMT) reduces HIV risk behaviors and improves access to HIV-related services among drug users. In this study, we assessed the uptake and willingness of MMT patients to refer HIV testing and counseling (HTC) service to their sexual partners and relatives.MethodsHealth status, HIV-related risk behaviors, and HTC uptake and referrals of 1,016 MMT patients in Hanoi and Nam Dinh were investigated. Willingness to pay (WTP) for HTC was elicited using a contingent valuation technique. Interval and logistic regression models were employed to determine associated factors.ResultsMost of the patients (94.2%) had received HTC, 6.6 times on average. The proportion of respondents willing to refer their partners, their relatives and to be voluntary peer educators was 45.7%, 35.3%, and 33.3%, respectively. Attending MMT integrated with HTC was a facilitative factor for HTC uptake, greater WTP, and volunteering as peer educators. Older age, higher education and income, and HIV positive status were positively related to willingness to refer partners or relatives, while having health problems (mobility, usual care, pain/discomfort) was associated with lower likelihood of referring others or being a volunteer. Over 90% patients were willing to pay an average of US $17.9 for HTC service.ConclusionThe results highlighted the potential role of MMT patients as referrers to HTC and voluntary peer educators. Integrating HIV testing with MMT services and applying users’ fee are potential strategies to mobilize resources and encourage HIV testing among MMT patients and their partners.     

Investigating CFTR and KCa3.1 Protein/Protein Interactions

In epithelia, Cl^- channels play a prominent role in fluid and electrolyte transport. Of particular importance is the cAMP-dependent cystic fibrosis transmembrane conductance regulator Cl^- channel (CFTR) with mutations of the CFTR encoding gene causing cystic fibrosis. The bulk transepithelial transport of Cl^- ions and electrolytes needs however to be coupled to an increase in K⁺ conductance in order to recycle K⁺ and maintain an electrical driving force for anion exit across the apical membrane. In several epithelia, this K⁺ efflux is ensured by K⁺ channels, including KCa3.1, which is expressed at both the apical and basolateral membranes. We show here for the first time that CFTR and KCa3.1 can physically interact. We first performed a two-hybrid screen to identify which KCa3.1 cytosolic domains might mediate an interaction with CFTR. Our results showed that both the N-terminal fragment M1-M40 of KCa3.1 and part of the KCa3.1 calmodulin binding domain (residues L345-A400) interact with the NBD2 segment (G1237-Y1420) and C- region of CFTR (residues T1387-L1480), respectively. An association of CFTR and F508del-CFTR with KCa3.1 was further confirmed in co-immunoprecipitation experiments demonstrating the formation of immunoprecipitable CFTR/KCa3.1 complexes in CFBE cells. Co-expression of KCa3.1 and CFTR in HEK cells did not impact CFTR expression at the cell surface, and KCa3.1 trafficking appeared independent of CFTR stimulation. Finally, evidence is presented through cross-correlation spectroscopy measurements that KCa3.1 and CFTR colocalize at the plasma membrane and that KCa3.1 channels tend to aggregate consequent to an enhanced interaction with CFTR channels at the plasma membrane following an increase in intracellular Ca²⁺ concentration. Altogether, these results suggest 1) that the physical interaction KCa3.1/CFTR can occur early during the biogenesis of both proteins and 2) that KCa3.1 and CFTR form a dynamic complex, the formation of which depends on internal Ca²⁺.     

Effect of water stress on the lipid and fatty acid composition of cotton (Gossypium hirsutum) chloroplasts

In order to investigate the effects of water stress on the photosynthetic compartment, analysis of chloroplast polar lipids and their fatty acid composition was made. Cotton ( Gossypium hirsutum L. cv. Reba) plants were submitted to water stress by witholding irrigation. Chloroplasts were purified on a Percoll gradient and three fractions were collected: intact, apparently intact and broken chloroplasts. The percentage of broken chloroplasts increased with a decrease in leaf water potential, indicating a greater weakness of the membrane. Galactolipid content (expressed as mg lipid per mg chlorophyll), particularly digalactosyldiglyceride, decreased with decreasing water potential. Phospholipid content decreased in the broken chloroplast fraction. The fatty acid composition of chloroplasts was also affected. The perecentage of linolenic acid (18:3), the major fatty acid of thylakoids, decreased, whereas that of linoleic acid(18:2) and oliec acid (18:1) increased. An accumulation of fatty acids having less than 16 carbon atoms was also observed. These changes in the lipid and fatty acid composition of cotton chloroplasts under water stress might affect the properties of the thylakoid membrane and thereby the photosynthetic activity and the compartmentation of the leaf cells.     

Microorganisms as Possible Indicators of General Soil Pollution by Dioxin-Containing Defoliants

The diversity of microorganisms from soils treated in the past with various dosages of dioxin-containing defoliants was studied. Population alterations dependent on dioxin concentrations were elucidated. Soil fungi and, to a smaller extent, actinomycetes were found to be the most sensitive to dioxins.     

The νSaα Specific Lipoprotein Like Cluster (lpl) of S. aureus USA300 Contributes to Immune Stimulation and Invasion in Human Cells

All Staphylococcus aureus genomes contain a genomic island, which is termed νSaα and characterized by two clusters of tandem repeat sequences, i.e. the exotoxin (set) and ''lipoprotein-like'' genes (lpl). Based on their structural similarities the νSaα islands have been classified as type I to IV. The genomes of highly pathogenic and particularly epidemic S. aureus strains (USA300, N315, Mu50, NCTC8325, Newman, COL, JH1 or JH9) belonging to the clonal complexes CC5 and CC8 bear a type I νSaα island. Since the contribution of the lpl gene cluster encoded in the νSaα island to virulence is unclear to date, we deleted the entire lpl gene cluster in S. aureus USA300. The results showed that the mutant was deficient in the stimulation of pro-inflammatory cytokines in human monocytes, macrophages and keratinocytes. Purified lipoprotein Lpl1 was further shown to elicit a TLR2-dependent response. Furthermore, heterologous expression of the USA300 lpl cluster in other S. aureus strains enhanced their immune stimulatory activity. Most importantly, the lpl cluster contributed to invasion of S. aureus into human keratinocytes and mouse skin and the non-invasive S. carnosus expressing the lpl gene cluster became invasive. Additionally, in a murine kidney abscess model the bacterial burden in the kidneys was higher in wild type than in mutant mice. In this infection model the lpl cluster, thus, contributes to virulence. The present report is one of the first studies addressing the role of the νSaα encoded lpl gene cluster in staphylococcal virulence. The finding that the lpl gene cluster contributes to internalization into non-professional antigen presenting cells such as keratinocytes highlights the lpl as a new cell surface component that triggers host cell invasion by S. aureus. Increased invasion in murine skin and an increased bacterial burden in a murine kidney abscess model suggest that the lpl gene cluster serves as an important virulence factor.     

Taxonomic diversity of aerobic organotrophic bacteria from clean vietnamese soils and their capacity for oxidation of petroleum hydrocarbons

The dominant species and abundance of the cultured aerobic organotrophic bacteria were determined in the clean soils of the Republic of Vietnam. The total number of organotrophs varied from 2.0 × 10⁵ to 5.8 × 10⁸ CFU/g soil. A considerable fraction of the bacterial population (1.1 × 10⁵–9.5 × 10⁶ CFU/g soil) was able to utilize petroleum hydrocarbons as the sole carbon and energy source. Most of the organisms obtained in pure cultures were gram-positive bacteria; over 70% were hydrocarbon-oxidizing organisms. Analysis of 16S rRNA gene sequences resulted in tentative determination of the taxonomic position of 22 strains, with 12 belonging to the Firmicutes, 4, to the Proteobacteria, and 6 to the Actinobacteria. The most common bacteria capable of hydrocarbon oxidation belonged to the genera Acinetobacter, Bacillus, Brevibacillus, Chromobacterium, Cupriavidus, Gordonia, Microbacterium, Mycobacterium, and Rhodococcus. Some of the isolated Bacillus and Staphylococcus strains, as well as one Pseudomonas and one Sinomonas strain, did not utilize hydrocarbons. Gram-positive degraders, especially members of the order Actinomycetales, which exhibited high hydrocarbon-oxidizing activity, gained competitive advantage in the presence of hydrocarbons. This microbial group probably plays an important role in hydrocarbon degradation in tropical soils. Thus, Vietnamese soils, which had no history of petroleum contamination, support numerically significant and taxonomically diverse populations of h ydrocarbon-oxidizing bacteria.     

Electrochemically amplified molecular beacon biosensor for ultrasensitive DNA sequence-specific detection of Legionella sp

An electrochemically amplified molecular beacon (EAMB) biosensor is constructed using thiolated hairpin DNA-ferrocene probes on gold electrode. The switching from "on" to "off" states of individual probes in the presence of complementary DNA target influences the electrode potential, besides the current, owing to changes in surface density of the electroactive hairpin DNA-ferrocene probes. The EAMB biosensor demonstrates linear range over 8 orders of magnitude with ultrasensitive detection limit of 2.3 × 10(-14)M for the quantification of a 21-mer DNA sequence. Its applicability is tested against PCR amplicons derived from genomic DNA of live Legionella pneumophila. Excellent specificity down to one and three nucleotides mismatches in another strain of L. pneumophila and a different bacterium species, respectively, is demonstrated.