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Signatures of aestivation and migration in Sahelian malaria mosquito populations

Nature advance online publication 26 November 2014. doi:10.1038/nature13987

Authors: A. Dao, A. S. Yaro, M. Diallo, S. Timbiné, D. L. Huestis, Y. Kassogué, A. I. Traoré, Z. L. Sanogo, D. Samaké & T. Lehmann

During the long Sahelian dry season, mosquito vectors of malaria are expected to perish when no larval sites are available; yet, days after the first rains, mosquitoes reappear in large numbers. How these vectors persist over the 3–6-month long dry season has not been resolved, despite extensive research for over a century. Hypotheses for vector persistence include dry-season diapause (aestivation) and long-distance migration (LDM); both are facets of vector biology that have been highly controversial owing to lack of concrete evidence. Here we show that certain species persist by a form of aestivation, while others engage in LDM. Using time-series analyses, the seasonal cycles of Anopheles coluzzii, Anopheles gambiae sensu stricto (s.s.), and Anopheles arabiensis were estimated, and their effects were found to be significant, stable and highly species-specific. Contrary to all expectations, the most complex dynamics occurred during the dry season, when the density of A. coluzzii fluctuated markedly, peaking when migration would seem highly unlikely, whereas A. gambiae s.s. was undetected. The population growth of A. coluzzii followed the first rains closely, consistent with aestivation, whereas the growth phase of both A. gambiae s.s. and A. arabiensis lagged by two months. Such a delay is incompatible with local persistence, but fits LDM. Surviving the long dry season in situ allows A. coluzzii to predominate and form the primary force of malaria transmission. Our results reveal profound ecological divergence between A. coluzzii and A. gambiae s.s., whose standing as distinct species has been challenged, and suggest that climate is one of the selective pressures that led to their speciation. Incorporating vector dormancy and LDM is key to predicting shifts in the range of malaria due to global climate change, and to the elimination of malaria from Africa.

Structural biology: Photosynthetic complex in close-up

Nature advance online publication 26 November 2014. doi:10.1038/nature14072

Author: Ilme Schlichting

Photosystem II, a photosynthetic protein complex, is prone to X-ray damage during crystallography. A high-resolution structure of the undamaged complex now offers a detailed view of its catalytic centre.

Materials science: Breakthrough for protons

Nature advance online publication 26 November 2014. doi:10.1038/nature14074

Author: Rohit N. Karnik

The atomically thin material called graphene is impermeable to atoms as small as helium. The finding that protons can pass through it might enable new kinds of membrane to be developed and aid research into fuel cells.

Microbiology: A beacon for bacterial tubulin

Nature advance online publication 26 November 2014. doi:10.1038/nature14071

Author: Elizabeth J. Harry

The protein FtsZ forms a ring structure that constricts to allow bacterial cells to divide. A second protein, MapZ, has now been found to guide FtsZ to the correct mid-cell position in the bacterium Streptococcus pneumoniae.

Malaria: How vector mosquitoes beat the heat

Nature advance online publication 26 November 2014. doi:10.1038/nature14073

Author: Nora J. Besansky

Intensive longitudinal sampling of malaria mosquitoes in the African semi-desert reveals that three morphologically indistinguishable species have distinctive strategies for surviving the dry season.

Editorial Expression of Concern: Non-adaptive origins of interactome complexity

Nature advance online publication 26 November 2014. doi:10.1038/nature13141

Authors: Ariel Fernández & Michael Lynch

Native structure of photosystem II at 1.95 Å resolution viewed by femtosecond X-ray pulses

Nature advance online publication 26 November 2014. doi:10.1038/nature13991

Authors: Michihiro Suga, Fusamichi Akita, Kunio Hirata, Go Ueno, Hironori Murakami, Yoshiki Nakajima, Tetsuya Shimizu, Keitaro Yamashita, Masaki Yamamoto, Hideo Ago & Jian-Ren Shen

Photosynthesis converts light energy into biologically useful chemical energy vital to life on Earth. The initial reaction of photosynthesis takes place in photosystem II (PSII), a 700-kilodalton homodimeric membrane protein complex that catalyses photo-oxidation of water into dioxygen through an S-state cycle of the oxygen evolving complex (OEC). The structure of PSII has been solved by X-ray diffraction (XRD) at 1.9 ångström resolution, which revealed that the OEC is a Mn4CaO5-cluster coordinated by a well defined protein environment. However, extended X-ray absorption fine structure (EXAFS) studies showed that the manganese cations in the OEC are easily reduced by X-ray irradiation, and slight differences were found in the Mn–Mn distances determined by XRD, EXAFS and theoretical studies. Here we report a ‘radiation-damage-free’ structure of PSII from Thermosynechococcus vulcanus in the S1 state at a resolution of 1.95 ångströms using femtosecond X-ray pulses of the SPring-8 ångström compact free-electron laser (SACLA) and hundreds of large, highly isomorphous PSII crystals. Compared with the structure from XRD, the OEC in the X-ray free electron laser structure has Mn–Mn distances that are shorter by 0.1–0.2 ångströms. The valences of each manganese atom were tentatively assigned as Mn1D(iii), Mn2C(iv), Mn3B(iv) and Mn4A(iii), based on the average Mn–ligand distances and analysis of the Jahn–Teller axis on Mn(iii). One of the oxo-bridged oxygens, O5, has significantly longer distances to Mn than do the other oxo-oxygen atoms, suggesting that O5 is a hydroxide ion instead of a normal oxygen dianion and therefore may serve as one of the substrate oxygen atoms. These findings provide a structural basis for the mechanism of oxygen evolution, and we expect that this structure will provide a blueprint for the design of artificial catalysts for water oxidation.

Proton transport through one-atom-thick crystals

Nature advance online publication 26 November 2014. doi:10.1038/nature14015

Authors: S. Hu, M. Lozada-Hidalgo, F. C. Wang, A. Mishchenko, F. Schedin, R. R. Nair, E. W. Hill, D. W. Boukhvalov, M. I. Katsnelson, R. A. W. Dryfe, I. V. Grigorieva, H. A. Wu & A. K. Geim

Graphene is increasingly explored as a possible platform for developing novel separation technologies. This interest has arisen because it is a maximally thin membrane that, once perforated with atomic accuracy, may allow ultrafast and highly selective sieving of gases, liquids, dissolved ions and other species of interest. However, a perfect graphene monolayer is impermeable to all atoms and molecules under ambient conditions: even hydrogen, the smallest of atoms, is expected to take billions of years to penetrate graphene’s dense electronic cloud. Only accelerated atoms possess the kinetic energy required to do this. The same behaviour might reasonably be expected in the case of other atomically thin crystals. Here we report transport and mass spectroscopy measurements which establish that monolayers of graphene and hexagonal boron nitride (hBN) are highly permeable to thermal protons under ambient conditions, whereas no proton transport is detected for thicker crystals such as monolayer molybdenum disulphide, bilayer graphene or multilayer hBN. Protons present an intermediate case between electrons (which can tunnel easily through atomically thin barriers) and atoms, yet our measured transport rates are unexpectedly high and raise fundamental questions about the details of the transport process. We see the highest room-temperature proton conductivity with monolayer hBN, for which we measure a resistivity to proton flow of about 10 Ω cm2 and a low activation energy of about 0.3 electronvolts. At higher temperatures, hBN is outperformed by graphene, the resistivity of which is estimated to fall below 10−3 Ω cm2 above 250 degrees Celsius. Proton transport can be further enhanced by decorating the graphene and hBN membranes with catalytic metal nanoparticles. The high, selective proton conductivity and stability make one-atom-thick crystals promising candidates for use in many hydrogen-based technologies.

Conductive two-dimensional titanium carbide ‘clay’ with high volumetric capacitance

Nature advance online publication 26 November 2014. doi:10.1038/nature13970

Authors: Michael Ghidiu, Maria R. Lukatskaya, Meng-Qiang Zhao, Yury Gogotsi & Michel W. Barsoum

Safe and powerful energy storage devices are becoming increasingly important. Charging times of seconds to minutes, with power densities exceeding those of batteries, can in principle be provided by electrochemical capacitors—in particular, pseudocapacitors. Recent research has focused mainly on improving the gravimetric performance of the electrodes of such systems, but for portable electronics and vehicles volume is at a premium. The best volumetric capacitances of carbon-based electrodes are around 300 farads per cubic centimetre; hydrated ruthenium oxide can reach capacitances of 1,000 to 1,500 farads per cubic centimetre with great cyclability, but only in thin films. Recently, electrodes made of two-dimensional titanium carbide (Ti3C2, a member of the ‘MXene’ family), produced by etching aluminium from titanium aluminium carbide (Ti3AlC2, a ‘MAX’ phase) in concentrated hydrofluoric acid, have been shown to have volumetric capacitances of over 300 farads per cubic centimetre. Here we report a method of producing this material using a solution of lithium fluoride and hydrochloric acid. The resulting hydrophilic material swells in volume when hydrated, and can be shaped like clay and dried into a highly conductive solid or rolled into films tens of micrometres thick. Additive-free films of this titanium carbide ‘clay’ have volumetric capacitances of up to 900 farads per cubic centimetre, with excellent cyclability and rate performances. This capacitance is almost twice that of our previous report, and our synthetic method also offers a much faster route to film production as well as the avoidance of handling hazardous concentrated hydrofluoric acid.

MapZ marks the division sites and positions FtsZ rings in Streptococcus pneumoniae

Nature advance online publication 26 November 2014. doi:10.1038/nature13966

Authors: Aurore Fleurie, Christian Lesterlin, Sylvie Manuse, Chao Zhao, Caroline Cluzel, Jean-Pierre Lavergne, Mirita Franz-Wachtel, Boris Macek, Christophe Combet, Erkin Kuru, Michael S. VanNieuwenhze, Yves V. Brun, David Sherratt & Christophe Grangeasse

In every living organism, cell division requires accurate identification of the division site and placement of the division machinery. In bacteria, this process is traditionally considered to begin with the polymerization of the highly conserved tubulin-like protein FtsZ into a ring that locates precisely at mid-cell. Over the past decades, several systems have been reported to regulate the spatiotemporal assembly and placement of the FtsZ ring. However, the human pathogen Streptococcus pneumoniae, in common with many other organisms, is devoid of these canonical systems and the mechanisms of positioning the division machinery remain unknown. Here we characterize a novel factor that locates at the division site before FtsZ and guides septum positioning in pneumococcus. Mid-cell-anchored protein Z (MapZ) forms ring structures at the cell equator and moves apart as the cell elongates, therefore behaving as a permanent beacon of division sites. MapZ then positions the FtsZ ring through direct protein–protein interactions. MapZ-mediated control differs from previously described systems mostly on the basis of negative regulation of FtsZ assembly. Furthermore, MapZ is an endogenous target of the Ser/Thr kinase StkP, which was recently shown to have a central role in cytokinesis and morphogenesis of S. pneumoniae. We show that both phosphorylated and non-phosphorylated forms of MapZ are required for proper Z-ring formation and dynamics. Altogether, this work uncovers a new mechanism for bacterial cell division that is regulated by phosphorylation and illustrates that nature has evolved a diversity of cell division mechanisms adapted to the different bacterial clades.

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