Characterization of Streptococcus pneumoniae 5-enolpyruvylshikimate 3-phosphate synthase and its activation by univalent cations.

The aroA gene (Escherichia coli nomenclature) encoding 5-enolpyruvylshikimate-3-phosphate (EPSP) synthase from the gram-positive pathogen Streptococcus pneumoniae has been identified, cloned and overexpressed in E. coli, and the enzyme purified to homogeneity. It was shown to catalyze a reversible conversion of shikimate 3-phosphate (S3P) and phosphoenolpyruvate (PEP) to EPSP and inorganic phosphate. Activation by univalent cations was observed in the forward reaction, with NH+4, Rb+ and K+ exerting the greatest effects. Km(PEP) was lowered by increasing [NH+4] and [K+], whereas Km(S3P) rose with increasing [K+], but fell with increasing [NH+4]. Increasing [NH+4] and [K+] resulted in an overall increase in kcat. Glyphosate (GLP) was found to be a competitive inhibitor with PEP, but the potency of inhibition was profoundly affected by [NH+4] and [K+]. For example, increasing [NH+4] and [K+] reduced Ki(GLP versus PEP) up to 600-fold. In the reverse reaction, the enzyme catalysis was less sensitive to univalent cations. Our analysis included univalent cation concentrations comparable with those found in bacterial cells. Therefore, the observed effects of these metal ions are more likely to reflect the physiological behavior of EPSP synthase and also add to our understanding of how to inhibit this enzyme in the host organism. As there is a much evidence to suggest that EPSP synthase is essential for bacterial survival, its discovery in the serious gram-positive pathogen S. pneumoniae and its inhibition by GLP indicate its potential as a broad-spectrum antibacterial target.     

Dynamic nuclear reorganization during genome remodeling of Tetrahymena

The single-celled ciliate Tetrahymena thermophila possesses two versions of its genome, one germline, one somatic, contained within functionally distinct nuclei (called the micronucleus and macronucleus, respectively). These two genomes differentiate from identical zygotic copies. The development of the somatic nucleus involves large-scale DNA rearrangements that eliminate 15 to 20 Mbp of their germline-derived DNA. The genomic regions excised are dispersed throughout the genome and are largely composed of repetitive sequences. These germline-limited sequences are targeted for removal from the genome by a RNA interference (RNAi)-related machinery that directs histone H3 lysine 9 and 27 methylation to their associated chromatin. The targeting small RNAs are generated in the micronucleus during meiosis and then compared against the parental macronucleus to further enrich for germline-limited sequences and ensure that only non-genic DNA segments are eliminated. Once the small RNAs direct these chromatin modifications, the DNA rearrangement machinery, including the chromodomain proteins Pdd1p and Pdd3p, assembles on these dispersed chromosomal sequences, which are then partitioned into nuclear foci where the excision events occur. This DNA rearrangement mechanism is Tetrahymena's equivalent to the silencing of repetitive sequences by the formation of heterochromatin. The dynamic nuclear reorganization that occurs offers an intriguing glimpse into mechanisms that shape nuclear architecture during eukaryotic development.     

Ciliate biology: dynamin goes nuclear

Dynamin and dynamin-related proteins (DRPs) mediate an array of membrane fission processes. A Tetrahymena DRP has adopted a new role, assisting in nuclear differentiation, a finding that further highlights these proteins - and this ciliate - as biological innovators.     

Degradation of Phthalic Acids by Denitrifying, Mixed Cultures of Bacteria

Mixed cultures of bacteria, enriched from aquatic sediments, grew anaerobically on all three isomers of phthalic acid. Each culture grew anaerobically on only one isomer and also grew aerobically on the same isomer. Pure cultures were isolated from the phthalic acid (o-phthalic acid) and isophthalic acid (m-phthalic acid) enrichments that grew aerobically on phthalic and isophthalic acids. Cell suspension experiments indicated that protocatechuate is an intermediate of aerobic catabolism. Pure cultures which grew aerobically on terephthalic acid (p-phthalic acid) could not be isolated from the enrichments, and neither could pure cultures that grew anaerobically on any of the isomers. Cell suspension experiments suggested that separate pathways exist for the aerobic and anaerobic oxidation of phthalic acids. Each enrichment culture used only one phthalic acid isomer under anaerobic conditions, but all isomers were simultaneously adapted for the anaerobic catabolism of benzoate. Cells grown anaerobically on a phthalic acid immediately attacked the isomer under anaerobic conditions, whereas there was a lag before aerobic breakdown occurred, and, for phthalic and terephthalic acids, chloramphenicol stopped aerobic adaptation but had no effect on anaerobic catabolism. This work suggests that phthalic acids are biodegradable in anaerobic environments.     

Acclimatization of Antarctic natural phytoplankton assemblages when exposed to solar ultraviolet radiation

The effects of solar ultraviolet radiation (UVR) on photosyntheticrates of natural assemblages of Antarctic phytoplankton weredetermined in both 1 day and 2 week incubations during australspring at Palmer Station, Antarctica. During the first day ofthe long-term incubations, photosynthetic rates were enhancedby     

A Systematic Review of Health System Barriers and Enablers for Antiretroviral Therapy (ART) for HIV-Infected Pregnant and Postpartum Women

Background

Despite global progress in the fight to reduce maternal mortality, HIV-related maternal deaths remain persistently high, particularly in much of Africa. Lifelong antiretroviral therapy (ART) appears to be the most effective way to prevent these deaths, but the rates of three key outcomes—ART initiation, retention in care, and long-term ART adherence—remain low. This systematic review synthesized evidence on health systems factors affecting these outcomes in pregnant and postpartum women living with HIV.

Methods

Searches were conducted for studies addressing the population of interest (HIV-infected pregnant and postpartum women), the intervention of interest (ART), and the outcomes of interest (initiation, adherence, and retention). Quantitative and qualitative studies published in English since January 2008 were included. A four-stage narrative synthesis design was used to analyze findings. Review findings from 42 included studies were categorized according to five themes: 1) models of care, 2) service delivery, 3) resource constraints and governance challenges, 4) patient-health system engagement, and 5) maternal ART interventions.

Results

Low prioritization of maternal ART and persistent dropout along the maternal ART cascade were key findings. Service delivery barriers included poor communication and coordination among health system actors, poor clinical practices, and gaps in provider training. The few studies that assessed maternal ART interventions demonstrated the importance of multi-pronged, multi-leveled interventions.

Conclusions

There has been a lack of emphasis on the experiences, needs and vulnerabilities particular to HIV-infected pregnant and postpartum women. Supporting these women to successfully traverse the maternal ART cascade requires carefully designed and targeted interventions throughout the steps. Careful design of integrated service delivery models is of critical importance in this effort. Key knowledge gaps and research priorities were also identified, including definitions and indicators of adherence rates, and the importance of cumulative measures of dropout along the maternal ART cascade.     

Homology modeling, simulation and molecular docking studies of catechol-2, 3-Dioxygenase from Burkholderia cepacia: Involved in degradation of Petroleum hydrocarbons

Catechol 2, 3-dioxygenase is present in several types of bacteria and undergoes degradation of environmental pollutants through an important key biochemical pathways. Specifically, this enzyme cleaves aromatic rings of several environmental pollutants such as toluene, xylene, naphthalene and biphenyl derivatives. Hence, the importance of Catechol 2, 3-dioxygenase and its role in the degradation of environmental pollutants made us to predict the three-dimensional structure of Catechol 2, 3-dioxygenase from Burkholderia cepacia. The 10ns molecular dynamics simulation was carried out to check the stability of the modeled Catechol 2, 3- dioxygenase. The results show that the model was energetically stable, and it attains their equilibrium within 2000 ps of production MD run. The docking of various petroleum hydrocarbons into the Catechol 2,3-dioxygenase reveals that the benzene, O-xylene, Toluene, Fluorene, Naphthalene, Carbazol, Pyrene, Dibenzothiophene, Anthracene, Phenanthrene, Biphenyl makes strong hydrogen bond and Van der waals interaction with the active site residues of H150, L152, W198, H206, H220, H252, I254, T255, Y261, E271, L276 and F309. Free energy of binding and estimated inhibition constant of these compounds demonstrates that they are energetically stable in their binding cavity. Chrysene shows positive energy of binding in the active site atom of Fe. Except Pyrene all the substrates made close contact with Fe atom by the distance ranges from 1.67 to 2.43 Å. In addition to that, the above mentioned substrate except pyrene all other made π-π stacking interaction with H252 by the distance ranges from 3.40 to 3.90 Å. All these docking results reveal that, except Chrysene all other substrate has good free energy of binding to hold enough in the active site and makes strong VdW interaction with Catechol-2,3-dioxygenase. These results suggest that, the enzyme is capable of catalyzing the above-mentioned substrate.     

Bathymetric adaptations of reef-building corals at davies reef,great barrier reef,Australia. II. Light saturation curves for photosynthesis and respiration

Light saturation (P-I) curves for oxygen production and consumption were constructed in the laboratory for corals collected from depths of 1 to 45 m on the southeastern (seaward) side of Davies Reef, Great Barrier Reef, Australia. This depth range represents a gradient of from 82.6 to 2.9% of surface light, which was measured as photosynthetic photon flux density (PPFD) between 400 and 700 nm. Adaptative changes in photokinetic parameters were observed over the entire range of light intensities. The compensation intensity (I_c), I_k, the intensity at which photosynthesis was 95% light saturated (I_0.95), and the respiration rate (?R), all decreased with decreasing light intensity. The maximal rate of photosynthesis when normalized on the basis of coral chlorophyll-a content (P_ma^g) tended to decrease with decreasing irradiance but the change was not statistically significant. The $\text{P}\text{R}$ ratio ($\text{P}{}_{\mathrm{m}}{}^{\mathrm{g}}\text{?R}$), the initial slope of a light saturation curve (α), and the maximum rate of photosynthesis when normalized by coral protein content (P_mp^g), all increased with decreasing light intensity. The logarithms of the values for each variable parameter were proportional to the logarithms of the fraction of the surface PPFD (T) transmitted to the depth at which the corals grew. This enabled changes in these parameters to be accurately estimated for corals growing at any depth on the reef. Comparison of experimental data with published values for “saturating” irradiance and P_ma^g, suggests that the endosymbiotic algae within reef-building corals are photosynthetically intermediate between classical “sun” and “shade” plants.