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The biofilm matrix can be considered to be a shared space for the encased microbial cells, comprising a wide variety of extracellular polymeric substances (EPS), such as polysaccharides, proteins, amyloids, lipids and extracellular DNA (eDNA), as well as membrane vesicles and humic-like microbially derived refractory substances. EPS are dynamic in space and time and their components interact in complex ways, fulfilling various functions: to stabilize the matrix, acquire nutrients, retain and protect eDNA or exoenzymes, or offer sorption sites for ions and hydrophobic substances. The retention of exoenzymes effectively renders the biofilm matrix an external digestion system influencing the global turnover of biopolymers, considering the ubiquitous relevance of biofilms. Physico-chemical and biological interactions and environmental conditions enable biofilm systems to morph into films, microcolonies and macrocolonies, films, ridges, ripples, columns, pellicles, bubbles, mushrooms and suspended aggregates — in response to the very diverse conditions confronting a particular biofilm community. Assembly and dynamics of the matrix are mostly coordinated by secondary messengers, signalling molecules or small RNAs, in both medically relevant and environmental biofilms. Fully deciphering how bacteria provide structure to the matrix, and thus facilitate and benefit from extracellular reactions, remains the challenge for future biofilm research.In this Review, Flemming et al. revisit our understanding of the biofilm matrix, focusing on the diversity of the extracellular polymeric substance components and novel aspects of mechanisms and consequences of their functional interactions.

Structures of voltage-gated sodium channelsIn “excitable” cells, like neurons and muscle cells, a difference in electrical potential is used to transmit signals across the cell membrane. This difference is regulated by opening or closing ion channels in the cell membrane. For example, mutations in human voltage-gated sodium (Nav) channels are associated with disorders such as chronic pain, epilepsy, and cardiac arrhythmia. Pan et al. report the high-resolution structure of a human Nav channel, and Shen et al. report the structures of an insect Nav channel bound to the toxins that cause pufferfish and shellfish poisoning in humans. Together, the structures give insight into the molecular basis of sodium ion permeation and provide a path toward structure-based drug discovery.Science, this issue p. eaau2486, p. eaau2596INTRODUCTIONThe nine subtypes of mammalian voltage-gated sodium (Nav) channels, Nav1.1 to Nav1.9, are responsible for the initiation and propagation of action potentials in specific excitable systems, among which Nav1.4 functions in skeletal muscle. Responding to membrane potential changes, Nav channels undergo sophisticated conformational shifts that lead to transitions between resting, activated, and inactivated states. Defects in Nav channels are associated with a variety of neurological, cardiovascular, muscular, and psychiatric disorders. In addition, Nav channels are targets for natural toxins and clinical therapeutics.Understanding the physiological and pathophysiological mechanisms of Nav channels requires knowing the structure of each conformational state. All eukaryotic Nav channels comprise a single polypeptide chain, the α subunit, that folds to four homologous repeats I to IV. Channel properties are modulated by one or two subtype-specific β subunits. Cryo–electron microscopy (cryo-EM) structures of two Nav channels, one from American cockroach and the other from electric eel, were resolved in two distinct conformations. However, the inability to record currents of either channel in heterologous systems prevented functional assignment of these structures. Structural elucidation of a functionally well-characterized Nav channel is required to establish a model for structure-function relationship studies.RATIONALEAfter extensive screening for expression systems, protein boundaries, chimeras, affinity tags, and combination with subtype-specific β subunits, we focused on human Nav1.4 in the presence of β1 subunit for cryo-EM analysis. The complex, which was transiently coexpressed in human embryonic kidney (HEK) 293F cells with BacMam viruses and purified through tandem affinity columns and size exclusion chromatography, was concentrated to ~0.5 mg/ml for cryo-EM sample preparation and data acquisition.RESULTSThe cryo-EM structure of human Nav1.4-β1 complex was determined to 3.2-Å resolution. The extracellular and transmembrane domains, including the complete pore domain, all four voltage-sensing domains (VSDs), and the β1 subunit, were clearly resolved, enabling accurate model building (see the figure).The well-resolved Asp/Glu/Lys/Ala (DEKA) residues, which are responsible for specific Na+ permeation through the selectivity filter, exhibit identical conformations to those seen in the other two Nav structures. A glyco-diosgenin (GDN) molecule, the primary detergent used for protein purification and cryo-EM sample preparation, penetrates the intracellular gate of the pore domain, holding it open to a diameter of ~5.6 Å. The central cavity of the pore domain is filled with lipid-like densities, which traverse the side wall fenestrations.Voltage sensing involves four to six Arg/Lys residues on helix S4 of the VSD. This helix moves “up” (away from the cytoplasm) in response to changes of the membrane potential, and this opens the channel finally. All four VSDs display up conformations. The movement of the gating charge residues is facilitated by coordination to acidic and polar residues on S1 to S3. The improved resolution allows detailed analysis of the coordination.The fast inactivation Ile/Phe/Met (IFM) motif on the short linker between repeats III and IV inserts into a hydrophobic cavity enclosed by the S6 and S4-S5 segments in repeats III and IV. Analysis of reported functional residues and disease mutations corroborates our recently proposed allosteric blocking mechanism for fast inactivation.CONCLUSIONThe structure provides important insight into the molecular basis for Na+ permeation, electromechanical coupling, asynchronous activation, and fast inactivation of the four repeats. It opens a new chapter for studying the structure-function relationships of Nav channels, affords an accurate template to map mutations associated with diseases such as myotonia and periodic paralysis hyperkalemic, and illuminates a path toward precise understanding and intervention with specific Nav channelopathies.Voltage-gated sodium (Nav) channels, which are responsible for action potential generation, are implicated in many human diseases. Despite decades of rigorous characterization, the lack of a structure of any human Nav channel has hampered mechanistic understanding. Here, we report the cryo–electron microscopy structure of the human Nav1.4-β1 complex at 3.2-Å resolution. Accurate model building was made for the pore domain, the voltage-sensing domains, and the β1 subunit, providing insight into the molecular basis for Na+ permeation and kinetic asymmetry of the four repeats. Structural analysis of reported functional residues and disease mutations corroborates an allosteric blocking mechanism for fast inactivation of Nav channels. The structure provides a path toward mechanistic investigation of Nav channels and drug discovery for Nav channelopathies.

In a many-body localized (MBL) quantum system, the ergodic hypothesis breaks down, giving rise to a fundamentally new many-body phase. Whether and under which conditions MBL can occur in higher dimensions remains an outstanding challenge both for experiments and theory. Here, we experimentally explore the relaxation dynamics of an interacting gas of fermionic potassium atoms loaded in a two-dimensional optical lattice with different quasiperiodic potentials along the two directions. We observe a dramatic slowing down of the relaxation for intermediate disorder strengths. Furthermore, beyond a critical disorder strength, we see negligible relaxation on experimentally accessible time scales, indicating a possible transition into a two-dimensional MBL phase. Our experiments reveal a distinct interplay of interactions, disorder, and dimensionality and provide insights into regimes where controlled theoretical approaches are scarce.

High-resolution transmission electron microscopy is an invaluable tool for looking at the crystalline structures of many materials. However, the need for high beam doses, especially as a sample is rotated to find the crystal axes, can lead to damage, particularly in fragile materials. Zhang et al. combined a state-of-the-art direct-detection electron-counting camera with ways to limit the overall electron dose to analyze delicate materials such as metal organic frameworks. With this approach, they could see the benzene rings in a UiO-66 linker and the coexistence of ligand-free (metal-exposing) and ligand-capped surfaces in UiO-66 crystals. Science , this issue p. 675 A direct-detection camera allows for high-resolution transmission electron microscopy imaging of beam-sensitive materials. High-resolution imaging of electron beam–sensitive materials is one of the most difficult applications of transmission electron microscopy (TEM). The challenges are manifold, including the acquisition of images with extremely low beam doses, the time-constrained search for crystal zone axes, the precise image alignment, and the accurate determination of the defocus value. We develop a suite of methods to fulfill these requirements and acquire atomic-resolution TEM images of several metal organic frameworks that are generally recognized as highly sensitive to electron beams. The high image resolution allows us to identify individual metal atomic columns, various types of surface termination, and benzene rings in the organic linkers. We also apply our methods to other electron beam–sensitive materials, including the organic-inorganic hybrid perovskite CH 3 NH 3 PbBr 3 .

Medium- and high-entropy alloys (M/HEAs) mix several principal elements with near-equiatomic composition and represent a model-shift strategy for designing previously unknown materials in metallurgy 1 – 8 , catalysis 9 – 14 and other fields 15 – 18 . One of the core hypotheses of M/HEAs is lattice distortion 5 , 19 , 20 , which has been investigated by different numerical and experimental techniques 21 – 26 . However, determining the three-dimensional (3D) lattice distortion in M/HEAs remains a challenge. Moreover, the presumed random elemental mixing in M/HEAs has been questioned by X-ray and neutron studies 27 , atomistic simulations 28 – 30 , energy dispersive spectroscopy 31 , 32 and electron diffraction 33 , 34 , which suggest the existence of local chemical order in M/HEAs. However, direct experimental observation of the 3D local chemical order has been difficult because energy dispersive spectroscopy integrates the composition of atomic columns along the zone axes 7 , 32 , 34 and diffuse electron reflections may originate from planar defects instead of local chemical order 35 . Here we determine the 3D atomic positions of M/HEA nanoparticles using atomic electron tomography 36 and quantitatively characterize the local lattice distortion, strain tensor, twin boundaries, dislocation cores and chemical short-range order (CSRO). We find that the high-entropy alloys have larger local lattice distortion and more heterogeneous strain than the medium-entropy alloys and that strain is correlated to CSRO. We also observe CSRO-mediated twinning in the medium-entropy alloys, that is, twinning occurs in energetically unfavoured CSRO regions but not in energetically favoured CSRO ones, which represents, to our knowledge, the first experimental observation of correlating local chemical order with structural defects in any material. We expect that this work will not only expand our fundamental understanding of this important class of materials but also provide the foundation for tailoring M/HEA properties through engineering lattice distortion and local chemical order. Atomic electron tomography is used to determine the 3D atomic positions and chemical species of medium- and high-entropy alloy nanoparticles and quantitatively characterize the local lattice distortion, strain tensor, twin boundaries, dislocation cores and chemical short-range order.

Radiocesium remediation is desirable for ecological protection, human health and sustainable development of nuclear energy. Effective capture of Cs + from acidic solutions is still challenging, mainly due to the low stability of the adsorbing materials and the competitive adsorption of protons. Herein, the rapid and highly selective capture of Cs + from strongly acidic solutions is achieved by a robust K + -directed layered metal sulfide KInSnS 4 (InSnS-1) that exhibits excellent acid and radiation resistance. InSnS-1 possesses high adsorption capacity for Cs + and can serve as the stationary phase in ion exchange columns to effectively remove Cs + from neutral and acidic solutions. The adsorption of Cs + and H 3 O + is monitored by single-crystal structure analysis, and thus the underlying mechanism of selective Cs + capture from acidic solutions is elucidated at the molecular level. The removal of radiocesium from acidic solutions is challenging. Here, the authors report the rapid and highly selective capture of cesium(I) from strongly acidic solutions by a robust layered metal sulfide.

Tropospheric nitrogen dioxide (NO2) column densities detected from space are widely used to infer trends in terrestrial nitrogen oxide (NO x ) emissions. We study changes in NO2 column densities using the Ozone Monitoring Instrument (OMI) over China from 2005 to 2015 and compare them with the bottom-up inventory to examine NO x emission trends and their driving forces. From OMI measurements we detect the peak of NO2 column densities at a national level in the year 2011, with average NO2 column densities deceasing by 32% from 2011 to 2015 and corresponding to a simultaneous decline of 21% in bottom-up emission estimates. A significant variation in the peak year of NO2 column densities over regions is observed. Because of the reasonable agreement between the peak year of NO2 columns and the start of deployment of denitration devices, we conclude that power plants are the primary contributor to the NO2 decline, which is further supported by the emission reduction of 56% from the power sector in the bottom-up emission inventory associated with the penetration of selective catalytic reduction (SCR) increasing from 18% to 86% during 2011–2015. Meanwhile, regulations for vehicles also make a significant contribution to NO x emission reductions, in particular for a few urbanized regions (e.g., Beijing and Shanghai), where they implemented strict regulations for vehicle emissions years before the national schedule for SCR installations and thus reached their NO2 peak 2–3 years ahead of the deployment of denitration devices for power plants.

The stacking between nanosheets is an intriguing and inevitable phenomenon in the chemistry of nano-interfaces. Two-dimensional metal-organic framework nanosheets are an emerging type of nanosheets with ultrathin and porous features, which have high potential in separation applications. Here, the stacking between single-layer metal-organic framework nanosheets is revealed to show three representative conformations with tilted angles of 8°, 14°, and 30° for Zr-1, 3, 5-(4-carboxylphenyl)-benzene framework as an example. Efficient untwisted stacking strategy by simple heating is proposed. A detailed structural analysis of stacking modes reveals the creation of highly ordered sub-nanometer micropores in the interspacing of untwisted nano-layers, yielding a high-resolution separator for the pair of para -/ meta -isomers over the twisted counterparts and commercial HP-5MS and VF-WAXMS columns. This general method is proven by additional nanosheet examples and supported by Grand Canonical Monte Carlo simulation. This finding will provide a synthetic route in the rational design of functionalities in two-dimensional metal-organic framework nanosheet. Metal-organic framework nanosheets are promising for separations, but interactions among them, affecting the performance, are largely unexplored. The authors reveal the favored stacking modes in a model system, and that untwisted restacking by thermal treatment improves isomer separation performance in gas chromatography capillary columns.

The sinking of organic particles formed in the photic layer is a main vector of carbon export into the deep ocean. Although sinking particles are heavily colonized by microbes, so far it has not been explored whether this process plays a role in transferring prokaryotic diversity from surface to deep oceanic layers. Using Illumina sequencing of the 16S rRNA gene, we explore here the vertical connectivity of the ocean microbiome by characterizing marine prokaryotic communities associated with five different size fractions and examining their compositional variability from surface down to 4,000 m across eight stations sampled in the Atlantic, Pacific, and Indian Oceans during the Malaspina 2010 Expedition. Our results show that the most abundant prokaryotes in the deep ocean are also present in surface waters. This vertical community connectivity seems to occur predominantly through the largest particles because communities in the largest size fractions showed the highest taxonomic similarity throughout the water column, whereas free-living communities were more isolated vertically. Our results further suggest that particle colonization processes occurring in surface waters determine to some extent the composition and biogeography of bathypelagic communities. Overall, we postulate that sinking particles function as vectors that inoculate viable particle-attached surface microbes into the deep-sea realm, determining to a considerable extent the structure, functioning, and biogeography of deep ocean communities.