Volume 531 Number 7592

Editorials

Future present p.7

A young global-sustainability platform deserves time to find its feet.

doi: 10.1038/531007b

Unintended consequences p.7

After the introduction of a clumsily worded new rule, the UK government should move quickly to reassure scientists that they can continue to advise policymakers.

doi: 10.1038/531007a

Brain power p.8

As brain stimulation finds non-medical uses, now is the time to consider its implications.

doi: 10.1038/531008a

News

News Features

Can fracking power Europe? p.22

Several countries hope to unleash vast natural-gas reserves through fracking, but drilling attempts have been disappointing.

doi: 10.1038/531022a

News & Views

Reactions triggered electrically p.38

Single-molecule experiments have revealed that chemical reactions can be controlled using electric fields — and that the reaction rate is sensitive to both the direction and the strength of the applied field. See Letter p.88

doi: 10.1038/531038a

Mitochondria in the second act p.39

A large phylogenomics study reveals that the symbiotic event that led to the emergence of organelles known as mitochondria may have occurred later in the evolution of complex cells than was thought. See Letter p.101

doi: 10.1038/nature16876

Dawn of a new astronomy p.40

The discovery of gravitational waves from a merging black-hole system opens a window on the Universe that promises to test gravity at its strongest, and to reveal many surprises about black holes and other astrophysical systems.

doi: 10.1038/nature17306

Dietary fat promotes intestinal dysregulation p.42

In mice, a high-fat diet has now been found to induce intestinal progenitor cells to adopt a more stem-cell-like fate, altering the size of the gut and increasing tumour incidence. See Article p.53

doi: 10.1038/531042a

Cosmic rays beyond the knees p.43

The development of a radio technique for detecting cosmic rays casts fresh light on the origins of some of these accelerated particles, and suggests that they might have travelled much farther than was previously thought. See Letter p.70

doi: 10.1038/531043a

Stem cells make the bowel nervous p.44

In Hirschsprung disease, the enteric nervous system (ENS) is missing from the distal bowel. It emerges that postnatal transplantation of stem-cell-derived ENS precursors can prevent death in a mouse model of the disease. See Letter p.105

doi: 10.1038/nature16877

Articles

Priming and polymerization of a bacterial contractile tail structure p.59

A combination of X-ray crystallography, electron microscopy, functional assays and time-lapse fluorescence microscopy shows that a protein of previously unknown function, TssA, forms a dodecameric complex that interacts with components of the tube and sheath of the type VI secretion system of bacteria, and that it primes and coordinates biogenesis of both the tail tube and the sheath.

doi: 10.1038/nature17182

Structural basis of outer membrane protein insertion by the BAM complex p.64

Two crystal structures of the Escherichia coli β-barrel assembly machinery (BAM complex) are presented, one of which includes all five subunits (BamA–BamE), in two distinct conformational states; together with functional assays and molecular dynamics stimulations, these structures help to generate a model for outer membrane protein insertion.

doi: 10.1038/nature17199

Letters

A large light-mass component of cosmic rays at 1017–1017.5 electronvolts from radio observations p.70

Cosmic rays are the highest-energy particles found in nature. Measurements of the mass composition of cosmic rays with energies of 1017–1018 electronvolts are essential to understanding whether they have galactic or extragalactic sources. It has also been proposed that the astrophysical neutrino signal comes from accelerators capable of producing cosmic rays of these energies. Cosmic rays initiate air showers—cascades of secondary particles in the atmosphere—and their masses can be inferred from measurements of the atmospheric depth of the shower maximum (Xmax; the depth of the air shower when it contains the most particles) or of the composition of shower particles reaching the ground. Current measurements have either high uncertainty, or a low duty cycle and a high energy threshold. Radio detection of cosmic rays is a rapidly developing technique for determining Xmax (refs 10, 11) with a duty cycle of, in principle, nearly 100 per cent. The radiation is generated by the separation of relativistic electrons and positrons in the geomagnetic field and a negative charge excess in the shower front. Here we report radio measurements of Xmax with a mean uncertainty of 16 grams per square centimetre for air showers initiated by cosmic rays with energies of 1017–1017.5 electronvolts. This high resolution in Xmax enables us to determine the mass spectrum of the cosmic rays: we find a mixed composition, with a light-mass fraction (protons and helium nuclei) of about 80 per cent. Unless, contrary to current expectations, the extragalactic component of cosmic rays contributes substantially to the total flux below 1017.5 electronvolts, our measurements indicate the existence of an additional galactic component, to account for the light composition that we measured in the 1017–1017.5 electronvolt range.

doi: 10.1038/nature16976

Controlling spin relaxation with a cavity p.74

By coupling donor spins in silicon to a superconducting microwave cavity and tuning the spins to the cavity resonance, the rate of spin relaxation is increased by three orders of magnitude compared to that of detuned spins; in such a regime, spontaneous emission of radiation is the dominant mechanism of spin relaxation.

doi: 10.1038/nature16944

Condensation on slippery asymmetric bumps p.78

A surface engineering approach is described that is inspired by the water-condensation capability of the bumps on desert beetles, the droplet transportation facilitated by cactus spines and the slippery coating of the pitcher plant, to produce a structure with many water-harvesting applications.

doi: 10.1038/nature16956

Stable amorphous georgeite as a precursor to a high-activity catalyst p.83

Hydroxycarbonate minerals such as zincian malachite and aurichalcite are well known precursors to catalysts for methanol-synthesis and low-temperature water–gas shift reactions; here, a supercritical antisolvent method is used to prepare highly stable georgeite—a hydroxycarbonate mineral that has hitherto been ignored because of its rarity, but which is found to be a superior catalyst precursor.

doi: 10.1038/nature16935

Electrostatic catalysis of a Diels–Alder reaction p.88

Theory suggests that many chemical reactions (not simply, as is often thought, redox reactions) might be catalysed by an applied electric field; experimental evidence for this is now provided from single-molecule studies of the formation of carbon–carbon bonds in a Diels–Alder reaction.

doi: 10.1038/nature16989

Evidence from cyclostomes for complex regionalization of the ancestral vertebrate brain p.97

The brain of the hagfish, a cyclostome related to the lamprey, develops domains equivalent to the median ganglionic eminence and the rhombic lip, resembling the brains of gnathostomes (jawed vertebrates), suggesting that brain regionalization in jawed vertebrates occurred before the divergence of cyclostomes and gnathostomes more than 500 million years ago.

doi: 10.1038/nature16518