Several aspects of the proposal, which aims to expand open access, require serious discussion and, in some cases, a rethink.
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CHEMISTRY
Layered material adsorbs radioactive strontium
Several options exist for removing radioactive strontium from nuclear waste. Sodium titanosilicate is a choice in acidic conditions, and antimony silicate for alkaline. However, an entire class of materials has hitherto been unexplored. Manolis Manos et al. report that the layered chalcogenide K2xMnxSn3−xS6 (x = 0.5–0.95), or KMS-1, is remarkably selective for strontium at both ends of the pH scale and competitive with commercial alternatives. KMS-1 forms hexagonal crystals of manganese, tin, and sulfur atoms, sandwiching disordered potassium ions that are free to exchange with ions in surrounding solvent. Among the radioactive ions present in nuclear waste, strontium is among the hardest to remove because of the overwhelming excess of competing nonradioactive ions such as sodium and magnesium. KMS-1 is strongly selective for strontium, possibly because strontium ions are softer Lewis acids than sodium and magnesium and are therefore more likely to associate with the sulfide ions. The authors tested KMS-1's capacity to adsorb strontium at low and high pH and found its “distribution coefficient,” a metric of adsorption, comparable with other alternatives at high pH and greatly superior at low pH. Bulk KMS-1 could be a cost-effective solution to selected nuclear waste problems, the authors say. — K.M.
Structure of layered manganese tin sulfide stuffed with strontium ions.
“Layered metal sulfides: Exceptionally selective agents for radioactive strontium removal” by Manolis J. Manos, Nan Ding, and Mercouri G. Kanatzidis (see pages 3696–3699)
ENGINEERING
Capillary forces and electric fields direct the formation of nanomaterials
Materials with microscopic structures such as microarray chips, electronic nanocircuitry, and nanofluid drug-delivery patches often rely on weak intermolecular forces to drive their assembly. An alternative to these forces, capillary action can bring particles in close contact with one another and cause them to arrange locally. However, capillary force-driven particle arrangement has several setbacks: The force can only be applied to large- or medium-sized particles (>10 μm). The spacing between particles cannot be easily adjusted with smaller particles, and the resulting material frequently contains defects. Nadine Aubry et al. overcame these complications by applying an external electric field perpendicular to the fluid interface on which the particles float. Glass grains, ranging in size from 2 to 80 μm, self-assembled and formed defect-free monolayers under the influence of the electric field, which ordered the particles by balancing attractive and repulsive forces. The hexagonal lattice spacing of the final material could be altered dynamically by varying the intensity of the electric field. The authors' manufacturing method will help spur the development of nanotechnologies that depend on precisely structured materials. — F.A.
Assembled monolayer with adjustable spacing.
“Micro- and nanoparticles self-assembly for virtually defect-free, adjustable monolayers” by N. Aubry, P. Singh, M. Janjua, and S. Nudurupati (see pages 3711–3714)
ENVIRONMENTAL SCIENCES
Probing microbial gene expression in seawater
Many microbial species that live in the ocean have not been cultivated in the laboratory. To study these elusive microbes, researchers have developed genomic methods for establishing genome content of these species from environmental samples, side-stepping the requirement of cultivation. This strategy, called “metagenomics,” reveals all the genes present in DNA but not those that are actually being expressed. Using a variation on genomic techniques, Jorge Frias-Lopez et al. have analyzed gene expression of the entire microbial community represented in seawater samples from the northern Pacific Ocean. From small quantities of isolated RNA transcripts, the authors determined that ≈50% of the isolated transcripts were unique and had never before been observed in ocean metagenomic surveys. They also detected expression of genes involved in key metabolic pathways—photosynthesis, carbon fixation, and nitrogen acquisition—as well as genes encoding unknown proteins. The authors say results demon-strate that analysis of microbial community transcripts, metatranscriptomics, can reveal important gene expression patterns and uncover new gene categories in microbial field samples, with important application in the study of diversity and genetic variability in natural microbial communities. — M.M.
Micrograph of marine microbial plankton.
“Microbial community gene expression in ocean surface waters” by Jorge Frias-Lopez, Yanmei Shi, Gene W. Tyson, Maureen L. Coleman, Stephan C. Schuster, Sallie W. Chisholm, and Edward F. DeLong (see pages 3805–3810)
MICROBIOLOGY
Sugar-coated gut bacteria
How surface molecules enable infectious microbes to succeed is a more thoroughly explored subject than how symbiotic bacteria use similar tactics to colonize a mammalian host. For example, the human symbiont Bacteroides fragilis, which aids its host in metabolizing carbohydrates and improving the immune system, expresses a variety of external polysaccharides on its capsule. These polysaccharides may have essential functions, say Cui Hua Liu et al., who report that B. fragilis has a highly regulated mechanism in place to ensure that at least one of its eight polysaccharides is expressed. Expression of seven of the eight polysaccharide biosynthesis operons is controlled by the invertase Mpi, which regulates expression by inverting promoters. The authors show that B. fragilis cultures fail to thrive when all polysaccharides are “off” at the same time. However, a new mutant strain emerges spontaneously from the culture, expressing a single polysaccharide, Psb. The authors found that the Psb promoter can be inverted by an enzyme related to Mpi. Although the strain expressing a single polysaccharide is capable of colonizing germ-free mice, it loses in competition with wild-type B. fragilis. Liu et al. suggest that polysaccharide variety on the bacterial surface may make some microbes more adaptable to changing conditions within the host intestine. — K.M.
Bacteroides fragilis surface capsule expression.
“Regulation of surface architecture by symbiotic bacteria mediates host colonization” by Cui Hua Liu, S. Melanie Lee, Jordan M. VanLare, Dennis L. Kasper, and Sarkis K. Mazmanian (see pages 3951–3956)
NEUROSCIENCE
Maturing brain network in adults
When a person is focused on performing a task, certain brain regions become more active. At the same time, other regions become less active. Collectively termed the “default network,” the less-active regions, many researchers argue, enable introspective mental activity. The default network is well connected in the adult brain, but not much is known about how the network develops in children. Damien Fair et al. provide a snapshot of the default network in early school-age children, 7–9 years old, that reveals much sparser connectivity than in the adult brain. The authors used blood oxygen level-dependent (BOLD) functional MRI to collect data on brain activity while subjects were at rest. To determine how brain regions were interconnected, they then cross-correlated the BOLD signals for all voxels. The authors found that, in the adult brain, the ventral medial prefrontal cortex (mPFC), an important part of the default network, was robustly connected to the rest of the network. In children, the ventral mPFC was isolated. Although some of the increasing connectivity of the default network with age may be due to myelination, much of the functional maturation has to do with “regional coactivation,” in which connections are strengthened with experience, the authors say. — K.M.
Functional connections are missing in children (Left) but are present in adults (Right).
“The maturing architecture of the brain's default network” by Damien A. Fair, Alexander L. Cohen, Nico U. F. Dosenbach, Jessica A. Church, Francis M. Miezin, Deanna M. Barch, Marcus E. Raichle, Steven E. Petersen, and Bradley L. Schlaggar (see pages 4028–4032)
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