Chlamydia trachomatis Infection of Endocervical Epithelial Cells Enhances Early HIV Transmission Events

Chlamydia trachomatis causes a predominantly asymptomatic, but generally inflammatory, genital infection that is associated with an increased risk for HIV acquisition. Endocervical epithelial cells provide the major niche for this obligate intracellular bacterium in women, and the endocervix is also a tissue in which HIV transmission can occur. The mechanism by which CT infection enhances HIV susceptibility at this site, however, is not well understood. Utilizing the A2EN immortalized endocervical epithelial cell line grown on cell culture inserts, we evaluated the direct role that CT-infected epithelial cells play in facilitating HIV transmission events. We determined that CT infection significantly enhanced the apical-to-basolateral migration of cell-associated, but not cell-free, HIV_BaL, a CCR5-tropic strain of virus, across the endocervical epithelial barrier. We also established that basolateral supernatants from CT-infected A2EN cells significantly enhanced HIV replication in peripheral mononuclear cells and a CCR5+ T cell line. These results suggest that CT infection of endocervical epithelial cells could facilitate both HIV crossing the mucosal barrier and subsequent infection or replication in underlying target cells. Our studies provide a mechanism by which this common STI could potentially promote the establishment of founder virus populations and the maintenance of local HIV reservoirs in the endocervix. Development of an HIV/STI co-infection model also provides a tool to further explore the role of other sexually transmitted infections in enhancing HIV acquisition.     

Staff Nurses’ Perceptions and Experiences about Structural Empowerment: A Qualitative Phenomenological Study

The aim of the study reported in this article was to investigate staff nurses’ perceptions and experiences about structural empowerment and perceptions regarding the extent to which structural empowerment supports safe quality patient care. To address the complex needs of patients, staff nurse involvement in clinical and organizational decision-making processes within interdisciplinary care settings is crucial. A qualitative study was conducted using individual semi-structured interviews of 11 staff nurses assigned to medical or surgical units in a 600-bed university hospital in Belgium. During the study period, the hospital was going through an organizational transformation process to move from a classic hierarchical and departmental organizational structure to one that was flat and interdisciplinary. Staff nurses reported experiencing structural empowerment and they were willing to be involved in decision-making processes primarily about patient care within the context of their practice unit. However, participants were not always fully aware of the challenges and the effect of empowerment on their daily practice, the quality of care and patient safety. Ongoing hospital change initiatives supported staff nurses’ involvement in decision-making processes for certain matters but for some decisions, a classic hierarchical and departmental process still remained. Nurses perceived relatively high work demands and at times viewed empowerment as presenting additional. Staff nurses recognized the opportunities structural empowerment provided within their daily practice. Nurse managers and unit climate were seen as crucial for success while lack of time and perceived work demands were viewed as barriers to empowerment.     

The molecular mechanism of the bicarbonate effect at the plastoquinone reductase site of photosynthesis

It has been known for some time that bicarbonate reverses the inhibition, by formate under HCO₃ ^--depletion conditions, of electron transport in thylakoid membranes. It has been shown that the major effect is on the electron acceptor side of photosystem II, at the site of plastoquinone reduction. After presenting a historical introduction, and a minireview of the bicarbonate effect, we present a hypothesis on how HCO₃ ^- functions in vivo as (a) a proton donor to the plastoquinone reductase site in the D1-D2 protein; and (b) a ligand to Fe²⁺ in the Q_A-Fe-Q_B complex that keeps the D1-D2 proteins in their proper functional conformation. They key points of the hypothesis are: (1) HCO₃ ^- forms a salt bridge between Fe²⁺ and the D2 protein. The carboxyl group of HCO₃ ^- is a bidentate ligand to Fe²⁺, while the hydroxyl group H-bonds to a protein residue. (2) A second HCO₃ ^- is involved in protonating a histidine near the Q_B site to stabilize the negative charge on Q_B. HCO₃ ^- provides a rapidly available source of H⁺ for this purpose. (3) After donation of a H⁺, CO₃ ^2- is replaced by another HCO₃ ^-. The high pKa of CO₃ ^2- ensures rapid reprotonation from the bulk phase. (4) An intramembrane pool of HCO₃ ^- is in equilibrium with a large number of low affinity sites. This pool is a H⁺ buffering domain functionally connecting the external bulk phase with the quinones. The low affinity sites buffer the intrathylakoid [HCO₃ ^-] against fluctuations in the intracellular CO₂. (5) Low pH and high ionic strength are suggested to disrupt the HCO₃ ^- salt bridge between Fe²⁺ and D₂. The resulting conformational change exposes the intramembrane HCO₃ ^- pool and low affinity sites to the bulk phase.Two contrasting hypotheses for the action of formate are: (a) it functions to remove bicarbonate, and the low electron transport left in such samples is due to the left-over (or endogenous) bicarbonate in the system; or (b) bicarbonate is less of an inhibitor and so appears to relieve the inhibition by formate. Hypothesis (a) implies that HCO₃ ^- is an essential requirement for electron transport through the plastoquinones (bound plastoquinones Q_A and Q_B and the plastoquinone pool) of photosystem II. Hypothesis (b) implies that HCO₃ ^- does not play any significant role in vivo. Our conclusion is that hypothesis (a) is correct and HCO₃ ^- is an essential requirement for electron transport on the electron acceptor side of PS II. This is based on several observations: (i) since HCO₃ ^-, not CO₂, is the active species involved (Blubaugh and Govindjee 1986), the calculated concentration of this species (220 M at pH 8, pH of the stroma) is much higher than the calculated dissociation constant (Kd) of 35–60 M; thus, the likelihood of bound HCO₃ ^- in ambient air is high; (ii) studies on HCO₃ ^- effect in thylakoid samples with different chlorophyll concentrations suggest that the left-over (or endogenous) electron flow in bicarbonate-depleted chloroplasts is due to left-over (or endogenous) HCO₃ ^- remaining bound to the system (Blubaugh 1987).Abbreviations DCMU 3-(3,4-dichlorophenyl)-1, 1-dimethylurea (common name: diuron) - PSII photosystem II - Q_A first plastoquinone electron acceptor of PSII - Q_B second plastoquinone acceptor of PS II     

Characterization of the histamine releasing effect of neurotensin in the rat heart

Bolus injections of neurotensin (NT) in the rat perfused heart elicited a transient, dose-dependent histamine release. The histamine releasing effect of NT appears to be independent of the heart rate and coronary perfusion pressure and it was not influenced by atropine, propanolol, prazosin, methysergide, ketanserin, indomethacin, morphine, lidocaine or by removal of the atria. However, it was potentiated by adenosine, inhibited by sub-stimulatory concentrations of NT and the mast cell membrane stabilizing drug cromoglycate but was unaltered by the calcium antagonist verapamil. The absence of calcium in the heart perfusate suppressed the histamine releasing effect of NT. These results suggest that the histamine releasing effect of NT in the rat heart results from a direct effect on ventricular mast cells and is calcium-dependent.     

Colorimetric determination of catechol siderophores in microbial cultures

A highly sensitive spectrophotometric method for the selective detection of catechol compounds such as catechol siderophores (e.g., enterobactin) is described. The basis of the method involves the ability of the vicinal aromatic hydroxyl groups under acidic conditions to bring about a reduction of Fe3+ (from ferric ammonium citrate) to Fe2+. Detection of Fe2+ in the presence of Fe3+ is made with 1,10-phenanthroline under previously established conditions. The assay mixture is heated at 60 degrees C for 1 h to accelerate the development of color which is subsequently measured at 510 nm. The Beer-Lambert law is obeyed over the range of 0.16 to 60 microM 2,3-dihydroxybenzoic acid. Compared to the Arnow nitration method, the assay is more responsive, is approximately seven times more sensitive, and is effective with catechols substituted at positions 3 and 4. The method gives positive results with catechols such as DL-DOPA, L-dopamine, (+/-)-epinephrine, and DL-norepinephrine. Very rapid color development is obtained with ascorbic acid and p-diols, while m-diols are poorly detected. Low degrees of reactivity are shown by hydroxylamino and hydroxamate compounds. Phenolic, sulfydryl, indolyl, and quinonyl derivatives do not interfere with the reaction. The method has been adapted to determine catechol compounds in the culture medium of bacterial cells grown at different iron concentrations.     

Two outer membrane transport systems for vitamin B12 in Salmonella typhimurium.

The involvement of an outer membrane transport component for vitamin B12 uptake in Salmonella typhimurium, analogous to the btuB product in Escherichia coli, was investigated. Mutants of S. typhimurium selected for resistance to bacteriophage BF23 carried mutations at the btuB locus (butBS) (formerly called bfe, at the analogous map position as the E. coli homolog) and were defective in high-affinity vitamin B12 uptake. The cloned E. coli btuB gene (btuBE) hybridized to S. typhimurium genomic DNA and restored vitamin B12 transport activity to S. typhimurium btuBS mutants. An Mr-60,000 protein in the S. typhimurium outer membrane was repressed by growth with vitamin B12 and was eliminated in a btuBS mutant. The btuBS product thus appears to play the same role in vitamin B12 transport by S. typhimurium as does the E. coli btuBE product. A second vitamin B12 transport system that is not present in E. coli was found by cloning a fragment of S. typhimurium DNA that complemented btuB mutants for vitamin B12 utilization. In addition to this plasmid with a 6-kilobase insert of S. typhimurium DNA, vitamin B12 utilization by E. coli btuB strains required the btuC and btuD products, necessary for transport across the cytoplasmic membrane, but not the btuE or tonB product. The plasmid conferred low levels of vitamin B12-binding and energy-dependent transport activity but not susceptibility to phage BF23 or utilization of dicyanocobinamide. The cloned S. typhimurium DNA encoding this new transport system did not hybridize to the btuBE gene or to E. coli chromosomal DNA and therefore does not carry the S. typhimurium btuBS locus. Increased production of an Mr -84,000 polypeptide associated with the outer membrane was seen. The new locus appears to be carried on the large plasmid in most S. typhimurium strains. Thus S. typhimurium possesses both high- and low-affinity systems for uptake of cobalamins across the outer membrane.     

Novel Miscanthus hybrids: Modelling productivity on marginal land in Europe using dynamics of canopy development determined by light interception

New biomass crop hybrids for bioeconomic expansion require yield projections to determine their potential for strategic land use planning in the face of global challenges. Our biomass growth simulation incorporates radiation interception and conversion efficiency. Models often use leaf area to predict interception which is demanding to determine accurately, so instead we use low-cost rapid light interception measurements using a simple laboratory-made line ceptometer and relate the dynamics of canopy closure to thermal time, and to measurements of biomass. We apply the model to project the European biomass potentials of new market-ready hybrids for 2020–2030. Field measurements are easier to collect, the calibration is seasonally dynamic and reduces influence of weather variation between field sites. The model obtained is conservative, being calibrated by crops of varying establishment and varying maturity on less productive (marginal) land. This results in conservative projections of miscanthus hybrids for 2020–2030 based on 10% land use conversion of the least (productive) grassland and arable for farm diversification, which show a European potential of 80.7–89.7 Mt year⁻¹ biomass, with potential for 1.2–1.3 EJ year⁻¹ energy and 36.3–40.3 Mt year⁻¹ carbon capture, with seeded Miscanthus sacchariflorus × sinensis displaying highest yield potential. Simulated biomass projections must be viewed in light of the field measurements on less productive land with high soil water deficits. We are attempting to model the results from an ambitious and novel project combining new hybrids across Europe with agronomy which has not been perfected on less productive sites. Nevertheless, at the time of energy sourcing issues, seed-propagated miscanthus hybrids for the upscaled provision of bioenergy offer an alternative source of renewable energy. If European countries provide incentives for growers to invest, seeded hybrids can improve product availability and biomass yields over the current commercial miscanthus variety.     

Toward the brave new zoo: Species program planning for reproductive technology development

This article outlines some of the advantages inherent in domestic animal reproductive technology development and compares them to the disadvantages in such development in wildlife species. Species program planning (as proposed by the American Association of Zoological Parks and Aquariums' Species Survival Plan) is offered as an important first step in organizing appropriate research toward reproductive technology development in wildlife species.