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     

Seasonality of phytoplankton in northern tundra ponds

Thermokarst ponds are the most abundant type of water body in the arctic tundra, with millions occurring in the coastal plains of Alaska, Northwest Territories and Siberia. Because ice covers of at least 2 m in thickness are formed at these latitudes, tundra ponds freeze solid every winter As a result, the growing season is shortened to a range of 60 to 100 days, during which time the photoperiod is altered to a prolonged light phase. Tundra ponds are generally close to neutral in pH and low in ions, contain dissolved gases near saturation and are nutrient poor. In low arctic ponds there are two phytoplankton biomass and primary production peaks, whereas they may be only one in the high arctic. Nanoplanktonic flagellates of the Chrysophyceae and Cryptophyceae dominate the maxima. The mid-summer decline in phytoplankton in the low arctic can be attributed to a combination of phosphorus limitation and heavy grazing pressure. The cryptomonad Rhodomonas minuta Skuja is one of the most widespread phytoplankters in tundra ponds. Because of the altered photoperiods, many species do not form resting spores prior to ice formation but survive freezing in the vegetative state.     

EFFECT OF TREE CANOPY REMOVAL BY GYPSY MOTH LARVAE ON THE MACROALGAE OF A RHODE ISLAND HEADWATER STREAM1

A spring-fed, headwater stream in central Rhode Island was examined during the period from June to October, 1979 to 1982. In the first two summers, a dense riparian canopy reduced the light penetration at the stream surface to a range of 5 to 18% of incident radiation. The lotic macroalgal community during this period was limited to 1 to 4 species covering < 1 to 35% of the stream bottom. However, in June and July, 1981, the surrounding leaf canopy was removed by a massive gypsy moth larval outbreak. Light penetration to the stream during this summer increased to 73% by early July, thereby resulting in a rise in water temperatures by 3.7°C. Even though there was a partial regrowth of leaves in late July and August of 1981, macroalgal cover values continued to rise to an early August peak of 80%. During the third summer, 88% of the macroalgal abundance could be attributed to illumination and water temperature. The filamentous diatom Funotia pectinalis ( O.F. Müll.) Rabh. was the predominant species in the midsummer of all four years, accounting for at least 60% of the total cover. In 1981. an important taxon was the desmid Hyalotheca dissiliens (S. Smith) Bréb., a species which was not seen in other years. A less severe gypsy moth defoliation occurred in 1982 but did not produce significant differences in light, temperature or macroalgal cover from 1979 and 1980. The results indicate that light and temperature can be limiting during the summer in spring-fed, headwater streams and that seed populations of some species are present in undetect-able levels during these periods of suboptimal growth conditions. In addition, it appears that stream macroalgal communities can be quite resilient, recovering rapidly following a major perturbation .     

Characteristics of softwater streams in Rhode Island II. Composition and seasonal dynamics of macroalgal communities

Forty stream segments in Rhode Island, U.S.A., were examined seasonally from June 1979 to March 1982. Thirty-nine species of macroalgae were collected, respresenting 25 genera. The composition of the lotic flora was 54% green algae, 31% red algae, 5% blue-green algae, 5% xanthophytes, 3% chrysophytes and 3% diatoms. The majority of these taxa (85%) were filamentous. From a biweekly examination of five stream segments, macroalgal communities could be grouped according to light regime. Species in unshaded streams exhibited little seasonality, whereas in streams shaded by one or more layers of riparian canopy, maxima in species numbers and abundance occurred during colder seasons. The most widespread and abundant species were the blue-green alga Phormidium retzii, the green alga Draparnaldia acuta, and the diatom Eunotia pectinalis. P. retzii and E. pectinalis were aseasonal annuals, while D. acuta was primarily a winter-spring form. It appears that pH is a major factor affecting broad geographic distribution patterns of stream macroalgae, whereas the light regime established by overhanging canopy is an important factor which influences localized abundance and seasonality of lotic macroalgal communities. Niche pre-emption appears to be a common mode of resource space division among stream macroalgae in Rhode Island. E. pectinalis is the strongly developed dominant in this drainage system.     

DISTRIBUTION AND SYSTEMATICS OF FRESHWATER CERAMIALES (RHODOPHYTA) IN NORTH AMERICA1

Twenty-five freshwater populations of Ceramiales were collected in North America, 24 of which were from the tropical rainforest region of Central America and the Caribbean. The streams tended to be moderate in mean current velocity (X?= 23.3 cm·S^?1) and maximum width (X?= 6.3 m) but high in temperature (X?= 23.1°C), pH (X?= 7.9), and specific conductance (X?= 320 μS·cm^?1). Three Bostrychia species were restricted to the Caribbean islands: B. moritziana (Sonder ex Kütz.) J. Ag. (syn. B. cornigera Mont. and B. radicans f. moliforme Post), with ecorticate indeterminate axes, monosiphonous ultimate branches, and cladohaptera; B. radicans (Mont.) Mont. (syn. B. leprieurii Mont and B. rivularis Harv.), with ecorticate and polysiphonous axes throughout and cladophaptera; and B. tenella (Lamour.) J. Ag., with corticate indeterminate axes, monosiphonous ultimate branches, and peripherohaptera. Ballia prieurii Kütz. was found in Belize and Costa Rica and was characterized by rebranched determinate laterals, opposite branching, and long apical cells (X?= 61 μm) and axial cells (X?= 43 μm). Caloglossa leprieurii (Mont.) J. Ag. was localized in Puerto Rico while. C. ogasawaerensis Okam. was collected only in Costa Rica. The two species were separated by site of branching (midrib vs. margin) and blade width (X?= 384 vs. 861 μm). Polysiphonia subtilissima Mont. from Florida and Jamaica had four pericentral cells, no cortication, rhizoids arising from pericentral cells, and branches initiated at trichoblast scars.     

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.     

DISTRIBUTION AND SYSTEMATICS OF THE FRESHWATER GENUS TUOMEYA (RHODOPHYTA,BATRACHOSPERMACEAE)1

Twenty-seven populations of Tuomeya, including the types of Tuomeya fluviatilis Harvey and Baileya americana Kützing, were analyzed from the entire known range of the genus: northern Newfoundland to northern Florida and east of the Mississippi River. Key morphological features were examined in detail since it has been recently proposed that Tuomeya should be reduced to a section of the genus Batrachospermum. Our observations confirmed the presence of several characteristics unique to Tuomeya: gametophyte development from a basal mass of undifferentiated cells rather than a chantransia stage, pseudoparenchymatous growth, and carpogonia with obliquely to perpendicularly attached trichogynes. Based on these findings, we conclude that the genus Tuomeya should be retained. Using multivariate morphometrics, two groupings were found that differed significantly in plant length (X = 14.1 and 24.1 mm, respectively). However, since there was no other morphometric, environmental, or geographic basis for separation of the groupings, only one species is recognized, T. americana (Kützing) Papenfuss. Populations tend to occur in large streams (>2.8 m wide) with low ion content (≤ 100 μS · cm^?1).