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InsideSelf-Cleaning Paint 2Methane Escapes from the Arctic 2Flower Picks its Pollinator 3Nanoparticles Activate Neurons 3Milky Way Has Corrugated Rings 5Do Saunas Lower Cardiac Risk? 6
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BRIEFINGS
Scientific American Briefings consists of summaries of recent peer-reviewed articles from the scientific literature. It draws these
summaries from the journals of Nature Publishing Group, including Nature, Nature
Medicine, Nature Physics and the Nature Reviews journals.
Mariette DiChristina Senior Vice President and Editor-in-Chief,
Scientific American
Philip Yam Managing Editor, Online, Scientific American
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and President, Scientific American
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and Business Development, Scientific American
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Scientific American
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NANOMATERIALS
Self-cleaning paint works in oilA COATING that can be easily applied to various surfaces re-pels water and dirt, even when exposed to oil.
Other water-repellent paints stop working in oil and are easily scratched. To overcome this, Ivan Parkin at University College London and his colleagues cov-ered titanium dioxide nanoparti-cles with a hydrophobic polymer and suspended the particles in ethanol.
They sprayed or painted the suspension onto hard surfaces such as glass and steel, and dipped soft fabric materials into it. The coating repelled water and dirt, and did so even after being exposed to oil. Bonding the coating to surfaces using commercial adhesives made the film resistant to scratches from a knife and sandpaper.
The material could be useful in industrial applications that involve harsh and oily environ-ments, the authors say.
—Corie Lok, Nature
■ Science, doi: 10.1126/science.aaa0946 (2015)
BIOPHYSICS
Chameleons tune cells to change hueCHAMELEONS CHANGE color by tuning nanoscopic structures in their skin cells to reflect dif-ferent wavelengths of light.
Michel Milinkovitch and his colleagues at the University of Geneva, Switzerland, studied skin cells of the panther chame-leon (Furcifer pardalis) from Madagascar. They found that the lizards have two layers of spe-
cialized cells called iridophores. Each layer contains light-re-flecting guanine nanocrystals. By altering the spacing between the crystals in the upper layer, the cells shift from reflecting blue light to reflecting yellow or red wavelengths, which interact with the chameleon’s yellow pig-ments. This produces a change in color from green (pictured, top) to yellow–orange (bottom). The deeper layer consists of cells that reflect a broad set of wave-lengths, particularly those in the near-infrared range.
The first layer of cells allows the animals to quickly switch be-tween camouflage and an osten-tatious display to attract mates or expel a rival male, whereas the second layer provides thermal protection.
—Boer Deng, Nature
■ Nature Commun, doi: 10.1038/ncomms7368 (2015)
BIOGEOCHEMISTRY
Methane’s great Arctic escapeMETHANE IS moving from thawing Arctic soils into lakes and could be released into the at-mosphere. Methane is a potent greenhouse gas, so this mecha-nism might exacerbate future Arctic warming.
A team led by Adina Paytan of the University of California,
Santa Cruz, found that levels of methane were higher in soils around Toolik Lake, Alaska, than in the lake water itself. Geo-chemical measurements sug-gested that the methane is trans-ported from the soil’s active layer, which freezes and thaws every year, into the lake and then into the atmosphere.
If that pattern holds true for other northern lakes, soil could have a bigger role in sending methane into Arctic air than pre-viously thought.
—Alexandra Witze, Nature
■ Proc Natl Acad Sci USA, doi: 10.1073/pnas.1417392112 (2015)
MATERIALS
Liquid metal motor moves by itselfA TINY drop of liquid metal can propel itself for more than an hour without external help.
Millimeter-scale motors could find uses as sensors, pumps and drug carriers, but they often require external drivers such as electric fields. Jing Liu and his colleagues at Ts-inghua University in Beijing cre-ated a 60-microlitre liquid-metal motor that drove itself at around 5 centimeters per second by ‘eating’ aluminum.
The team applied flakes of alu-minum to droplets of an alloy of gallium and indium. A chemical reaction between the aluminum,
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Chameleons tune nanoscopic structures on their skin to reflect different wavelengths of light, enabling them to change from green (top) to yellow–orange (bottom).
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At Lake Toolik, Alaska, exogenous methane in groundwater affects the overall lake methane budget.
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A coating that can be easily applied to various surfaces repels water and dirt, even when exposed to oil, which may be useful in industrial settings that include harsh and oily environments. See page 2.
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Scientific American Briefings, Volume 4, Number 12, March 30, 2015, published weekly by Scientific American, a division of Nature America, Inc., 75 Varick Street, 9th Floor, New York, NY 10013-1917. Subscription rates: 1 year (50 issues) $79 (USD). Please send subscription correspondence, including change of e-mail and postal addresses to: Scientific American Briefings, Box 3187, Harlan, IA 51537. E-mail address for subscription inquires: [email protected]. E-mail address for general inquires: [email protected]. Subscription inquires: U.S. and Canada: 800-333-1199; other: +1-515-248-7684.
Copyright © 2015 Scientific American, a division of Nature America, Inc. All rights reserved.
BRIEFINGS
the alloy and a surrounding elec-trolyte propelled the metal beads around a Petri dish or through zig-zag and U-shaped channels.
The authors say that the work is a step towards creating a self-powered soft robot that can change shape according to its environment.
—Elizabeth Gibney, Nature
■ Adv Mater, doi: 10.1002/adma.201405438 (2015)
CHEMISTRY
Metal frame-work zaps nerve agentsA CRYSTALLINE compound cat-alyzes the destruction of a nerve agent much faster than other clean-up chemicals do.
Omar Farha and Joseph Hupp at Northwestern Univer-sity in Evanston, Illinois, and their colleagues studied a metal–organic framework (MOF) — a porous network of metal nodes linked by organic groups. They found that their zirconium-con-taining MOF broke down half of a simulant of the chemical war-fare agent DMNP in 15 minutes. Breakdown of 50% of the nerve agent GD took just 3 minutes.
Experiments and calculations showed that this MOF performs quickly because the zirconium ion active sites, which catalyze the breakdown reactions, are more easily reached by the nerve agents than in other MOFs.
—Corie Lok, Nature
■ Nature Mater, doi: 10.1038/nmat4238 (2015)
MARINE MICROBIOLOGY
Microbes lurk deep below the seaMICROBIAL LIFE may exist far deeper in the ocean floor than is often assumed.
Steven D’Hondt at the Uni-versity of Rhode Island in Narra-gansett and his colleagues sam-pled sediments across the southern Pacific Ocean. They found that oxygen, and microbes that require it, permeated depths of up to 75 meters below the sea floor — more than double previous estimates.
The team found that oxygen penetrates the entire sediment column where the sediment ac-cumulates slowly in a shallow layer. On this basis, the authors estimate that microbes that use oxygen may exist at low, but measurable, amounts throughout sediment in around 15–44% of the Pacific and in 9–37% of the global sea floor.
—Daniel Cressey, Nature
■ Nature Geosci, doi: 10.1038/ngeo2387 (2015)
ECOLOGY
Flowers choose the best pollinatorsA TROPICAL flower can turn on reproduction after it has been visited by a high-quality pollinator.
Matthew Betts of Oregon State University in Corvallis and his colleagues focused on the plant Heliconia tortuosa (pic-tured) and collected 148 of its pollinators, comprising six hum-mingbird species and one spe-cies of butterfly. The animals were cleaned of any pollen and introduced to aviaries con-taining flowers that had been
hand-pollinated. The plants showed signs of successful re-production only after their nectar had been drunk by hum-mingbird species with long curved beaks, such as the green hermit (Phaethornis guy; pic-tured). Hummingbirds without the specialized bills and butter-flies took in less nectar and failed to trigger reproduction.
Preferred birds also have the widest ranges, suggesting that the plants are boosting their chances of receiving pollen from distant flowers with more ge-netic diversity than nearby plants.
—Emma Marris, Nature
■ Proc Natl Acad Sci USA, doi: 10.1073/pnas.1419522112 (2015)
NEUROSCIENCE
Nanoparticles turn on neuronsGOLD NANOPARTICLES can be attached to neurons and used to stimulate the cells, without in-troducing any genes.
Current ‘optogenetic’ methods use light to excite spe-cific neurons, but genes must first be inserted into the cells to make them sensitive to light. To develop an alternative method, Francisco Bezanilla at the Uni-versity of Chicago in Illinois, David Pepperberg at the Univer-sity of Illinois at Chicago and their colleagues used molecules including antibodies to attach 20-nanometer-wide gold spheres to three different ion channels on the surface of cultured neu-
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rons. When the researchers flashed a millisecond pulse of light, the gold heated up, causing most of the neurons to fire. The same thing happened when they injected the nanoparticles into a specific region of a mouse brain slice.
—Alison Abbott, Nature
■ Neuron, doi: 10.1016/ j.neuron.2015.02.033 (2015)
EVOLUTION
Polyploid gainsTHE INDUCTION of polyploidy — that is, duplication or acquisi-tion of entire sets of chromo-somes — is a common event in the evolutionary histories of var-ious species. The evolutionary consequences of polyploidization have mostly been inferred based on correlations with adaptive transitions during evolution. A new study uses experimental evolution in yeast to directly demonstrate that polyploidy can promote adaptation.
Selmecki et al. used strains of Saccharomyces cerevisiae that were haploid (1N), diploid (2N) or tetraploid (4N) but were oth-erwise isogenic. For each ploidy type, cells expressing either yellow fluorescent protein (YFP) or cyan fluorescent protein (CFP) were mixed at a 50/50 ratio and used to seed >170 repli-cate cultures. These cultures were monitored by flow cytom-etry for up to 250 generations to test how rapidly the strains
adapted to the poor carbon source raffinose, as inferred by a skewing of the 50/50 colour ratio when a beneficial mutation arose and became positively se-lected in the cell population.
Overall, the tetraploid strains showed faster adaptation to this environment than the diploid or haploid strains. The authors’ simulation analysis suggested that this was caused by benefi-cial mutations occurring at a higher frequency and with greater effects on fitness.
Consistent with these hypoth-eses, sequencing of the strains confirmed that the evolving tet-raploid strains accumulated the most genetic diversity (com-prising focal mutations up to gains or losses of entire chromo-somes). Furthermore, the au-thors showed that introducing some of the identified beneficial mutation candidates into the ini-tial strains provided the greatest selective advantage to tetraploid cells.
Such effects on adaptation might also be relevant to poly-ploid pathogens or cancer cells.
—Darren J. Burgess, Nature
■ Nature, doi: 10.1038/nature14187 (2015)
ACUTE CORONARY SYNDROMES
Risks linked to NSAID use after heart attackASSOCIATION BETWEEN non-steroidal anti-inflammatory drug (NSAID) use and increased risk of serious bleeding has been as-sessed in patients who have ex-perienced a myocardial infarc-tion (MI). “Regardless of the an-tithrombotic treatment regimen, we found that addition of NSAIDs was associated with in-creased risks of bleeding,” con-clude the investigators from the retrospective Danish nationwide registry study. “Although it seems unlikely that physicians
can completely avoid prescrip-tion of NSAIDs, even among high-risk patients, these results highlight the importance of con-sidering the balance of benefits and risks before initiating any NSAID treatment.”
The study cohort consisted of 61,971 individuals aged ≥30 years (mean age 67.7 years) who were admitted to hospital with a first-time MI between 2002 and 2011. After discharge from hos-pital, the majority of patients were taking dual antiplatelet therapy (aspirin + clopidogrel; 64.9%), but some patients were taking single antithrombotic therapy (20.2%), triple anti-thrombotic therapy (8.5%), an oral anticoagulant and a single antiplatelet therapy (4.4%), or no antithrombotic therapy at all (2.0%). Median duration of follow-up was 3.5 years. Despite many medical authorities and societies (including the Danish Society of Cardiology) discour-aging NSAID use in patients with cardiovascular disease, one-third of the cohort made at least one prescription claim for NSAID treatment during follow-up.
The primary outcome of the study was bleeding events that required patient hospitalization and/or resulted in death. Com-pared with no use of NSAIDs, NSAID use was associated with increased risk of serious bleeding (HR 2.02, 95% CI 1.81–2.26). All types of NSAIDs, and all durations of their use, were associated with this increased bleeding risk. Notably, even
The concept behind attaching gold spheres to neurons.
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short-term NSAID use (0–3 days) was associated with substan-tially increased likelihood of se-rious bleeding (HR 3.37, 95% CI 2.57–4.41).
“Our results suggest that no safe treatment period exists,” highlight the investigators. “This is particularly worrying because in many countries ibu-profen is available without pre-scription in pharmacies and re-tail outlets.”
—Bryony M. Mearns, Nature Reviews Cardiology
■ JAMA, doi: 10.1001/jama.2015.0809 (2015)
ASTRONOMY
Milky Way has corrugated ringsTHE MILKY Way’s stars sprawl outwards in a series of concen-tric ripples, hinting that it might extend farther into space than was thought.
Data from the Sloan Digital Sky Survey confirm a previously known ring of stars at about 9,000 parsecs from the Sun. They also show another ring about 14,000 parsecs from the Sun, says a team led by Yan Xu of the National Astronomical Ob-servatories of China in Beijing. These rings each form a ripple, making our Galaxy corrugated rather than flat.
The ripples may have formed when a dwarf galaxy passed through the Milky Way, creating
rings of stars with its gravita-tional pull.
—Alexandra Witze, Nature
■ Astrophys J, doi: 10.1088/0004-637X/801/2/105 (2015)
MICROBIOTA
Sewage comes up smelling like roses for microbiota researchCHARACTERIZING THE human microbiome—to better under-stand its relationship with health and disease—is often achieved by assessing stool sam-ples from individuals. In a novel strategy to develop a population-based approach, Newton and col-leagues have used high-throughput 16S ribosomal (r)RNA sequencing to analyze sewage samples from 71 US cities.
Limited resources hamper the collection of enough indi-vidual samples to create mean-ingful population-level data. The investigators argue that sewage could be used as an alternative. Although only 15% of the sewage sample was of human origin, 97% of human fecal microbial rRNA oligotypes were identified. Having taken this into account when comparing sewage with in-dividual stool results, a compa-rable microbial community was found in both datasets.
Within datasets, less vari-ability existed between US city sewage samples than between individual stool samples. The main bacterial families found in each sewage sample were either Bacteroidaceae, Prevotellaceae or Lachnospiraceae plus Ruminococcaceae.
Could any population demo-graphics be associated with the sewage microbial profile? A small proportion of the vari-
ability between city samples pre-dicted (with an accuracy of 81–89%) whether the sample came from a lean or obese population.
The authors write that “com-parative sewage analysis pro-vides a unique opportunity to ex-plore the relationship between fecal communities and lifestyle or demographic differences in human populations”.
—Gillian Patman, Nature Reviews Gastroenterology &
Hepatology
■ mBio, doi: 10.1128/mBio.02574-14 (2015)
TRAUMATIC BRAIN INJURY
Cerebral blood flow linked to sports-related concussions THE RATE of restoration of normal cerebral blood flow (CBF) correlates with cognitive and behavioral outcomes after sports-related concussion, a new report in JAMA Neurology re-veals. In a study conducted in collegiate American footballers, Timothy Meier and colleagues found that incomplete resolution of CBF abnormalities by 1 month after concussion was associated with delayed return to play and more-severe initial mood symp-toms. The results indicate that CBF could provide a prognostic biomarker for recovery after concussion.
“A reduction of CBF, known as hypoperfusion, has been con-sistently demonstrated in pre-vious work in both animals and
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humans following more-severe forms of traumatic brain injury,” says Meier. “However, the time-frame for recovery of CBF fol-lowing sports-related concussion had not really been investigated, especially immediately postinjury.”
The investigators recruited 44 male athletes from an Amer-ican football team in the Na-tional Collegiate Athletic Associ-ation (NCAA) Division I. 17 of the participants sustained a concus-sion during play, and the re-maining 27 were included in the study as healthy controls.
Follow-up assessments were scheduled for 1 day, 1 week and 1 month after concussion. At each visit, CBF was measured by means of arterial spin labelling MRI, and the participants also underwent neuropsychiatric and cognitive evaluations. Of the ath-letes with concussion, 13 com-pleted all three of the assess-ments, and all 17 attended at least two of the three follow-up sessions. Assessment of concus-sion severity was based on be-havioral scores at the first post-concussion visit, and outcomes were categorized as good or poor, depending the time taken to return to play (≤14 days and >14 days, respectively).
In the athletes with concus-sion, reduced CBF was observed in the right dorsal midinsular cortex (dmIC) and superior tem-poral sulcus during the first week after injury. In most cases, CBF in these regions had re-turned to normal levels by 1 month after concussion. In a subset of participants, however, CBF in the dmIC remained below pre-injury levels at 1 month, and the persistent CBF impairment was associated with poor return-to-play outcomes, as well as symptoms of anxiety and depression at the initial assessment.
“These data suggest that mea-surement of CBF has clinical po-tential for the management of
concussed athletes,” concludes Meier. “As a next step, we are trying to initiate a large-scale program in Albuquerque, New Mexico, in which all NCAA Divi-sion I athletes would be scanned at the start of the season, during any concussive events, and at the end of the season.” The re-searchers are also hoping to ex-tend their studies to high-school athletes.
—Heather Wood, Nature Reviews Neurology
■ JAMA Neurol, doi: 10.1001/jamaneurol.2014.4778 (2015)
RISK FACTORS
Saunas and lower cardio-vascular mortalityINCREASED FREQUENCY and duration of sauna bathing is as-sociated with a reduced risk of sudden cardiac death (SCD), fatal coronary heart disease (CHD), and fatal cardiovascular disease (CVD). This finding comes from the prospective Finnish Kuopio Ischemic Heart Disease Risk Factor Study.
The investigators recruited 2,315 middle-aged men (aged 42–60 years) between March 1984 and December 1989 from Eastern Finland. During follow-up (mean 20.7 years), 601 partici-pants had a sauna once per week, 1,513 had a sauna 2–3 times per week, and 201 had a sauna 4–7 times per week. Also during this period, 190, 281, 407, and 929 participants died from SCD, CHD, CVD, or any cause, respectively. Compared with those who had a sauna once per week, men who had a sauna 2–3 times per week or 4–7 times per week had a significantly reduced risk of SCD (HR 0.78 and 0.37), fatal CHD (HR 0.77 and 0.52), fatal CVD (HR 0.73 and 0.50), and all-cause mortality (HR 0.76
and 0.60). Moreover, longer du-ration of sauna bathing (>19 min) was associated with a re-duced risk of SCD, fatal CHD, and fatal CVD (but not all-cause mortality) compared with shorter duration.
Long-term sauna bathing has been shown to lower blood pres-sure and enhance left ventric-ular and endothelial function. The investigators conclude that “sauna bathing is a recommend-able health habit”, but further studies involving women and those unaccustomed to sauna bathing are needed.
—Gregory B. Lim, Nature Reviews Cardiology
■ JAMA Intern Med, doi: 10.1001/jamainternmed.2014.8187 (2015)
ANTIBACTERIAL IMMUNITY
A pinch of saltWE ARE all familiar with the negative effects of a diet high in salt — from increased risk of car-diovascular disease to worsening of autoimmune disease — so why have humans evolved to store high levels of salt in the body, particularly in the skin? New evi-dence points to a role for salt in contributing to cutaneous anti-bacterial defenses.
In patients with bacterial skin infections, 23Na magnetic resonance imaging and 23Na spectroscopy showed that, inde-pendently of the diet, the skin of the infected leg had marked Na+ accumulation compared with the contralateral uninfected leg and that this was decreased after antibiotic treatment. Further-
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more, mice with skin wounds had an increased salt concentra-tion in the affected skin com-pared with intact skin. Thus, in both humans and mice, immune cells entering infected and/or in-flamed skin are exposed to a high-salt environment.
To test the effect of this in vitro, lipopolysaccharide (LPS)-activated bone marrow-derived mouse macrophages were cul-tured in high-salt medium (with a 40 mM increase in NaCl con-centration), which increased ni-
tric oxide synthase 2 (Nos2) ex-pression and the production of nitric oxide (NO) compared with culture in normal-salt medium. Increased Nos2 transcription was associated with increased histone H3 lysine 4 trimethyl-ation of the Nos2 gene in the presence of high salt levels.
Next, the authors showed that high salt levels augment macrophage activation by in-creasing LPS-induced activation of p38 mitogen-activated protein kinase (MAPK) and of nuclear factor of activated T cells 5 (NFAT5), of which Nos2 is a known target gene. Decreasing or increasing NFAT5 levels in LPS-stimulated macrophages in-hibited or promoted, respec-tively, the increased NO produc-tion in a high-salt environment.
The increased NO production by macrophages in high-salt me-dium promoted the elimination of intracellular Escherichia coli, and
of Leishmania major infection in a p38 MAPK- and NFAT5-depen-dent manner. In an in vivo model, mice fed a high-salt diet had im-proved resolution of a footpad in-fection with L. major compared with mice fed a low-salt diet, and this correlated with increased salt concentration in the skin and in-creased levels of Nfat5 mRNA and NOS2. This beneficial effect was mitigated in mice with a myeloid cell-specific deletion of Nfat5.
So a ‘pinch’ of endogenous salt really could be good for you in terms of skin defense. How-ever, given the health risks of in-creasing salt in the diet, local ap-plication of salt to infected tis-sues might be more suitable as an approach to therapeutically target this pathway.
—Kirsty Minton, Nature Reviews Immunology
■ Cell Metab, doi: 10.1016/ j.cmet.2015.02.003 (2015)
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