Fumarate metabolism and ATP production in Pseudomonas fluorescens exposed to nitrosative stress

Although nitrosative stress is known to severely impede the ability of living systems to generate adenosine triphosphate (ATP) via oxidative phosphorylation, there is limited information on how microorganisms fulfill their energy needs in order to survive reactive nitrogen species (RNS). In this study we demonstrate an elaborate strategy involving substrate-level phosphorylation that enables the soil microbe Pseudomonas fluorescens to synthesize ATP in a defined medium with fumarate as the sole carbon source. The enhanced activities of such enzymes as phosphoenolpyruvate carboxylase and pyruvate phosphate dikinase coupled with the increased activities of phospho-transfer enzymes like adenylate kinase and nucleoside diphophate kinase provide an effective strategy to produce high energy nucleosides in an O₂-independent manner. The alternate ATP producing machinery is fuelled by the precursors derived from fumarate with the aid of fumarase C and fumarate reductase. This metabolic reconfiguration is key to the survival of P. fluorescens and reveals potential targets against RNS-resistant organisms.     

Microtubules are an intracellular target of the plant terpene citral

Citral is a component of plant essential oils that possesses several biological activities. It has known medicinal traits, and is used as a food additive and in cosmetics. Citral has been suggested to have potential in weed management, but its precise mode of action at the cellular level is unknown. Here we investigated the immediate response of plant cells to citral at micromolar concentrations. It was found that microtubules of Arabidopsis seedlings were disrupted within minutes after exposure to citral in the gaseous phase, whereas actin filaments remained intact. The effect of citral on plant microtubules was both time‐ and dose‐dependent, and recovery only occurred many hours after a short exposure of several minutes to citral. Citral was also able to disrupt animal microtubules, albeit less efficiently. In addition, polymerization of microtubules in vitro was inhibited in the presence of citral. Taken together, our results suggest that citral is a potent, volatile, anti‐microtubule compound.     

The Earliest Lead Object in the Levant

In the deepest section of a large complex cave in the northern Negev desert, Israel, a bi-conical lead object was found logged onto a wooden shaft. Associated material remains and radiocarbon dating of the shaft place the object within the Late Chalcolithic period, at the late 5^th millennium BCE. Based on chemical and lead isotope analysis, we show that this unique object was made of almost pure metallic lead, likely smelted from lead ores originating in the Taurus range in Anatolia. Either the finished object, or the raw material, was brought to the southern Levant, adding another major component to the already-rich Late Chalcolithic metallurgical corpus known to-date. The paper also discusses possible uses of the object, suggesting that it may have been used as a spindle whorl, at least towards its deposition.     

On the Apportionment of Population Structure

Measures of population differentiation, such as F_ST, are traditionally derived from the partition of diversity within and between populations. However, the emergence of population clusters from multilocus analysis is a function of genetic structure (departures from panmixia) rather than of diversity. If the populations are close to panmixia, slight differences between the mean pairwise distance within and between populations (low F_ST) can manifest as strong separation between the populations, thus population clusters are often evident even when the vast majority of diversity is partitioned within populations rather than between them. For any given F_ST value, clusters can be tighter (more panmictic) or looser (more stratified), and in this respect higher F_ST does not always imply stronger differentiation. In this study we propose a measure for the partition of structure, denoted E_ST, which is more consistent with results from clustering schemes. Crucially, our measure is based on a statistic of the data that is a good measure of internal structure, mimicking the information extracted by unsupervised clustering or dimensionality reduction schemes. To assess the utility of our metric, we ranked various human (HGDP) population pairs based on F_ST and E_ST and found substantial differences in ranking order. E_ST ranking seems more consistent with population clustering and classification and possibly with geographic distance between populations. Thus, E_ST may at times outperform F_ST in identifying evolutionary significant differentiation.     

A GxxxG-like Motif within HIV-1 Fusion Peptide Is Critical to Its Immunosuppressant Activity,Structure, and Interaction with the Transmembrane Domain of the T-cell Receptor

To thrive in the human body, HIV fuses to its target cell and evades the immune response via several mechanisms. The fusion cascade is initiated by the fusion peptide (FP), which is located at the N-terminal of gp41, the transmembrane protein of HIV. Recently, it has been shown that the HIV-1 FP, particularly its 5–13 amino acid region (FP_5–13), suppresses T-cell activation and interacts with the transmembrane domain (TMD) of the T-cell receptor (TCR) complex. Specific amino acid motifs often contribute to such interactions in TMDs of membrane proteins. Using bioinformatics and experimental studies, we report on a GxxxG-like motif (AxxxG), which is conserved in the FP throughout different clades and strains of HIV-1. Biological activity studies and FTIR spectroscopy revealed that HIV FP_5–13-derived peptides, in which the motif was altered either by randomization or by a single amino acid shift, lost their immunosuppressive activity concomitant with a loss of the β-sheet structure in a membranous environment. Furthermore, fluorescence studies revealed that the inactive mutants lost their ability to interact with their target site, namely, the TMD of TCRα, designated CP. Importantly, lipotechoic acid activated macrophages (lacking TCR) were not affected by FP, further demonstrating the specificity of the immunosuppressant activity of CP. Finally, although the AxxxG WT and the GxxxG analog both associated with the CP and immunosuppressed T-cells, the AxxxG WT but not the GxxxG analog induced lipid mixing. Overall, the data support an important role for the AxxxG motif in the function of FP and might explain the natural selection of the AxxxG motif rather than the classical GxxxG motif in FP.     

Lower leaf gas‐exchange and higher photorespiration of treated wastewater irrigated Citrus trees is modulated by soil type and climate

Water quality, soil and climate can interact to limit photosynthesis and to increase photooxidative damage in sensitive plants. This research compared diffusive and non‐diffusive limitations to photosynthesis as well as photorespiration of leaves of grapefruit trees in heavy clay and sandy soils having a previous history of treated wastewater (TWW) irrigation for >10 years, with different water qualities [fresh water (FW) vs TWW and sodium amended treated wastewater (TWW + Na)] in two arid climates (summer vs winter) and in orchard and lysimeter experiments. TWW irrigation increased salts (Na⁺ and Cl⁻), membrane leakage, proline and soluble sugar content, and decreased osmotic potentials in leaves of all experiments. Reduced leaf growth and higher stomatal and non‐stomatal (i.e. mesophyll) limitations were found in summer and on clay soil for TWW and TWW + Na treatments in comparison to winter, sandy soil and FW irrigation, respectively. Stomatal closure, lower chlorophyll content and altered Rubisco activity are probable causes of higher limitations. On the other hand, non‐photochemical quenching, an alternative energy dissipation pathway, was only influenced by water quality, independent of soil type and season. Furthermore, light and CO₂ response curves were investigated for other possible causes of higher non‐stomatal limitation. A higher proportion of non‐cyclic electrons were directed to the O₂ dependent pathway, and a higher proportion of electrons were diverted to photorespiration in summer than in winter. In conclusion, both diffusive and non‐diffusive limitations contribute to the lower photosynthetic performance of leaves following TWW irrigation, and the response depends on soil type and environmental factors.     

Significance of SIMS microscopy for the radioiodine detection in animal and human thyroid tissue.

We defined the SIMS conditions for radioiodine detection in animal and man thyroid follicles, in tissue sections (3 microns) chemically fixed and resin embedded. Two radioisotopes were tested: 125I and 129I, of high (14 mCi 125I micrograms-1) and low specific activity (1.07 10(-6) mCi 129I micrograms-1). In animal study, Wistar rats fed a normal iodine diet (10 micrograms 127I day-1) were injected ip 24 h before sacrifice either with 125I (7 10(-3) micrograms) or with 129I at a dose identical to iodine diet (10 micrograms) or 3 times higher (30 micrograms). No SIMS signal of 125I was obtained in vivo due to its too low concentration, while radioiodine distribution was evidenced with both doses of 129I. Local concentration of previously stored 127I in follicular lumen was not modified, when compared to control (4.14 +/- 0.03 micrograms/mg, m +/- SE), by 125I or 129I at a dose of 10 micrograms, but was nearly doubled with 129I at a dose of 30 micrograms, proof of a pharmacological effect on thyroid iodine regulation. In human study 129I was excluded due to its long half-life (1.6 10(7) years), and 125I was tested only in vitro on two surgical specimens of normal perinodular thyroid tissue maintained in mini-organ culture for 48 h in presence of 100 microCi/ml of 125I. The 125I was detectable, its concentration was 1,000-fold higher than that of 127I (1.5 +/- 0.004 micrograms/mg). For both in vivo and in vitro studies, a positive correlation exists between newly organified radioiodine (125I or 129I) and previously stored iodine (127I).(ABSTRACT TRUNCATED AT 250 WORDS)