In This Issue
APPLIED PHYSICAL SCIENCES
Unusual property of supercooled water
Despite the ubiquity of water, many of its physical properties are still not fully understood. Sow-Hsin Chen et al. have found that supercooled water, kept in a liquid state despite being well below its freezing point, violates the Stokes–Einstein relation and undergoes a glass-like, fragile-to-strong transition around the temperature of 225 K. The Stokes–Einstein relation ties together diffusion, viscosity, and temperature and is typically accurate for normal- and high-temperature liquids. Chen et al. confined water samples in a nanosized pore to prevent it from freezing at very cold temperatures, providing experimental access to liquid water at temperatures at which it is normally solid cubic ice. The authors found a well defined decoupling of transport properties of water, which implies a breakdown of the Stokes–Einstein relation. They also used the measurements to study water’s fragile-to-strong transition temperature, which they found to be ≈225 K. At this temperature, water’s hydrogen-bonding structure changes, marking a phase change from low-density liquid to high-density liquid. The Stokes–Einstein relation broke down in different ways on each side of the transition temperature. The authors say their results support the hypothesis that normal water exists as a mixture of these two liquid phases. — P.D.
“The violation of the Stokes–Einstein relation in supercooled water” by Sow-Hsin Chen, Francesco Mallamace, Chung-Yuan Mou, Matteo Broccio, Carmelo Corsaro, Antonio Faraone, and Li Liu (see pages 12974–12978)
ECOLOGY
Bacterial biodiversity predicted by ocean conditions
Environmental factors such as temperature, nutrient availability, and interspecies competition play a major role in animal and plant biodiversity. Although bacteria contribute to a wide variety of ecosystem processes, the effects of these factors on bacterial biodiversity have not been well understood. By studying the ocean waters off the southern coast of California, Jed Fuhrman et al. show that marine bacterioplankton exhibit strong patterns in distribution and abundance associated with oceanic environmental factors. Over 4.5 years, the authors took monthly water samples, filtered them free of eukaryotes, categorized the remaining bacteria into taxonomic units by DNA fingerprinting, and tested the samples for a suite of oceanographic environmental variables including temperature, salinity, dissolved oxygen, chlorophyll, bacterial heterotrophic production, and nutrients. Fuhrman et al. found that these factors had predictive values; the environmental conditions could predict the distribution and abundance of sets of bacterial taxonomic units, and, conversely, the diversity of the taxonomic units predicted not only the month the sample was collected but also the likely environmental conditions at the time of collection. These results demonstrate that bacterial communities operate much like animal and plant communities, in which the biodiversity of an ecosystem relies on environmental cues. — F.A.
Ocean environment and bacterial diversity.
“Annually reoccurring bacterial communities are predictable from ocean conditions” by Jed A. Fuhrman, Ian Hewson, Michael S. Schwalbach, Joshua A. Steele, Mark V. Brown, and Shahid Naeem (see pages 13104–13109)
MEDICAL SCIENCES
Bone marrow progenitor cells contribute to blood vessels
Endothelial progenitor cells play an important role in vascular development and repair and have potential uses in targeted therapies. Alexis Bailey et al. have isolated common myeloid (CMP) and granulocyte/macrophage (GMP) progenitors that can give rise to vascular endothelial cells. To discern endothelial progenitor activity in distinct bone marrow populations, Bailey et al. fractionated genetically tagged myeloid progenitors according to cell surface marker expression. After transplanting the cells into irradiated mice, myeloid progenitor cells, the differentiated progeny of hematopoietic stem cells, were found to produce endothelial cells. This differentiation occurred independent of cell fusion between the transplanted myeloid cells and host endothelial cells. The liver portal veins of recipient animals contained up to 1.3% donor-derived endothelial cells when transplanted with CMPs or GMPs. In addition, nonirradiated mice that were surgically joined (from shoulder to thigh) for 12 weeks, separated, and then analyzed 4–6 months later displayed nearly 4% donor-derived endothelial cells. Because myeloid progenitor cells can infiltrate both healthy and diseased tissues, these findings may aid in the treatment of vascular diseases by providing clues to vessel regeneration. — F.A.
Endothelial cell derived from stem cell progeny.
“Myeloid lineage progenitors give rise to vascular endothelium” by Alexis S. Bailey, Holger Willenbring, Shuguang Jiang, Daniel A. Anderson, David A. Schroeder, Melissa H. Wong, Markus Grompe, and William H. Fleming (see pages 13156–13161)
NEUROSCIENCE
Examining spontaneous and evoked neuron rewiring
During development, neurons must make connections with other cells to properly relay signals and wire a functioning brain. Jean-Vincent Le Bé and Henry Markram investigated how neurons choose their targets and found a high degree of plasticity, or ability to rewire connections. Neuronal axons extend to all neighboring dendrites numerously and with equal affinity, suggesting that neurons may not preferentially grow toward a specific receiver, but instead they stand ready for a connection to any dendrite at any time. To test this idea, Le Bé and Markram measured neuronal connections in the brains of rats and found that, within hours, new connections were spontaneously formed and old ones were discontinued many times, at all points along a specific neuron. To specifically evoke neuronal rewiring, glutamate was used, and its application increased the rate of new connections, suggesting that this connection rate is subject to modulation. After some time, weaker connections disappeared, and the connection rate returned to baseline levels. The authors hypothesize that new experiences trigger an increase in network connections that are then pruned as they are tested with repeated experience, shaping pathways in a Darwinian fashion. — T.D.
Assessing neuronal connections.
“Spontaneous and evoked synaptic rewiring in the neonatal neocortex” by Jean-Vincent Le Bé and Henry Markram (see pages 13214–13219)
PHARMACOLOGY
Galantamine protects against organophosphorus poisoning
Organophosphorus compounds (OPs) include the deadly nerve agents soman and sarin, which have been used in insecticides and biochemical warfare. These toxicants irreversibly inhibit the acetylcholinesterase enzyme, leading to loss of muscle control and adverse CNS effects, followed by coma and death. Galantamine, which is approved for use in treating Alzheimer’s disease, reversibly inhibits acetylcholinesterase in the brain and the periphery and prevents seizures and neurodegeneration. Edson Albuquerque et al. studied the ability of galantamine to counteract OP toxicity in guinea pigs. The authors found that the guinea pigs survived acute exposure to lethal doses of OPs when given moderate doses of galantamine plus atropine before or after the exposure. Galantamine appeared more effective than pyridostigmine, the currently approved regimen for soldiers, and less toxic than huperzine. Albuquerque et al. say the galantamine/atropine combination may be a safe and effective countermeasure against OP intoxication. — P.D.
Galantamine-treated cells protected against degeneration.
“Effective countermeasure against poisoning by organophosphorus insecticides and nerve agents” by Edson X. Albuquerque, Edna F. R. Pereira, Yasco Aracava, William P. Fawcett, Maristela Oliveira, William R. Randall, Tracey A. Hamilton, Robert K. Kan, James A. Romano, Jr., and Michael Adler (see pages 13220–13225)
