This Week in Science

Science  14 May 2004:
Vol. 304, Issue 5673, pp. 923
  1. Running on Asphalt


    Biological communities form in a variety of deep-sea settings, most notably associated with mid-ocean ridge hydrothermal systems, but also in other areas of hydrothermal vents and seeps on continental margins and off axis discharge from oceanic crust. They also occur locally in association with other food sources, such as decaying whale carcasses. MacDonald et al. (p. 999) now describe another process that provides fuel for life in the deep ocean—asphalt volcanism. A large area of solidified asphalt that flows in the southern Gulf of Mexico supports a deep-sea biota. The asphalt, associated with petroleum generation in the region, erupted on the sea floor at temperatures high enough to form prominent joints upon cooling, and solidifies upon contact with seawater. Such processes in asphalt volcanic fields may be widespread in the abyssal Gulf of Mexico, and perhaps in other areas with abundant petroleum resources.

  2. Loosely Connected Liquid Water?

    In an ice cube, the water molecules in the bulk are tetrahedrally coordinated and make both donor and acceptor hydrogen bonds, but the surface molecules have one free O-H group. Wernet et al. (p. 995, published online 1 April 2004; see the Perspective by Zubavicus and Grunze) have studied liquid water using near-edge x-ray fine-structure spectroscopy and nonresonant x-ray Raman scattering and find that most molecules (80 to 85%) look much like those on an ice surface; they form one strong donor and one strong acceptor hydrogen bond. The remainder are tetrahedrally coordinated. These findings are consistent with previous x-ray and neutron diffraction studies but appear to disagree with recent simulation studies that find a greater extent of tetrahedral bonding in the liquid phase.

  3. Linking Channels in Large-Pore Zeolites

    The usefulness of zeolites in processing the large hydrocarbons found in petroleum could likely be enhanced if their pores could be made larger. Many large-pore zeolites are known but they have systems of one-dimensional (1D) channels that do not intersect, which leads to diffusion limitations. Paillaud et al. (p. 990) now report that the incorporation of germanium as well as silicon during zeolite synthesis, under direction of an organic template, leads to thermally stable materials containing large-pore 2D channel networks. Aluminum can also be incorporated into these materials.

  4. Hydrothermal Routes to Higher Hydrocarbons

    Industrially, a process known as Fischer-Tropsch synthesis can be used to make higher hydrocarbons from carbon (coal) or carbon monoxide by reacting a fluid over an iron-cobalt catalyst at high temperatures. Whether (and where) such a reaction might produce higher hydrocarbons in the Earth has been uncertain. Foustoukos and Seyfried (p. 1002, published online 1 April 2004; see the Perspective by Sherwood Lollar) show experimentally that iron-chromium minerals (for example, chromite) can catalyze the production of propane from typical hydrothermal fluids. Similar reactions would be expected within the deeper layers of the oceanic crust and could provide higher hydrocarbons to hydrothermal vents and help feed their distinctive communities.

  5. Every Breath You Take...

    Despite decades of intensive research, the components of urban air pollution that cause the most damage to human health remain uncertain. A previous study showed that mice exposed for 10 weeks to ambient air at an industrial site near a major highway developed twice as many germline mutations at a genetic marker than did mice in a rural environment. By repeating the study with high-efficiency particulate-air filters, Somers et al. (p. 1008; see the Perspective by Samet et al.) identify the culprit mutagen as airborne particulate matter—microscopic, breathable particles of soot and dust that are often attached to toxic chemicals such as polycyclic aromatic hydrocarbons. Whether particulate air pollution poses a similar genetic risk in humans is not yet clear but merits further study.

  6. Regulating Phagosome Maturation

    Toll-like receptors (TLRs) play important roles in pathogen recognition. Now Blander and Medzhitov (p. 1014; see the cover and the Perspective by Watts) suggest an additional role for TLRs—the control of phagocytosis, the process by which cells engulf large particles, such as bacteria. TLR signaling was found to regulate phagosome maturation and phagolysosomal fusion in mouse macrophages through spatially restricted signaling pathways. The nature of the cargo appears to determine the fate of the phagosome, such that pathogens and apoptotic cells are delivered into separate phagosomes that undergo distinct modes of maturation.

  7. The Coast Is Clearing CO2


    The CO2 removed from the atmosphere by coastal seas has been shown in earlier studies to be disproportionately high for the area these seas cover, but those studies were not based on measurements over all seasons. Thomas et al. (p. 1005) conducted a yearlong campaign in the North Sea in order to assess and explain the air-sea flux of CO2 there. The North Sea took up approximately three times more CO2 per area unit than the ocean average, and is a remarkably efficient CO2 pump that transported 95% of the absorbed CO2 to the North Atlantic Ocean. Extrapolation of these data suggest that coastal seas worldwide remove 20% of the total CO2 absorbed by the ocean.

  8. Limiting the Red Queen's Domain?

    The Red Queen hypothesis accounts for the evolution of sex as a mechanism by which species can evolve more rapidly in response to interacting species. Sex would allow species to “run” as fast as they can and help them to keep abreast of surrounding species. Despite its widespread popularity, no general theoretical basis for the Red Queen hypothesis has been developed. Using a combination of analytical and numerical methods, Otto and Nuismer (p. 1018) explore the Red Queen hypothesis across a diverse array of coevolutionary genetic systems, types of ecological interactions, and parameter values. They find that the Red Queen fails, in most cases, to favor the evolution of sex and recombination.

  9. Subunits Solve Synaptic Secret


    Neuroscientist have long struggled with the conundrum that the same receptor can mediate opposing changes in synaptic efficacy, sometimes producing long-term potentiation (LTP) and sometimes producing long-term depression (LTD). Liu et al. (p. 1021; see the Perspective by Bliss and Schoepfer) found evidence in hippocampal brain slices for the presence of two mechanistically distinct plasticity mechanisms involving N-methyl-D-aspartate subtype glutamate (NMDA) receptors with different subunit compositions. LTP requires NMDA receptors that contain the NR2A subunit, whereas LTD requires NMDA receptors containing NR2B. The results provide a rationale for regional differences in plasticity and for developmental changes in the polarity of synaptic change.

  10. Memory Consolidation in Drosophila

    In Drosophila, a number of different memories have been described in recent years. However, the relation between these memories has not been fully clarified yet. Isabel et al. (p. 1024) show that long-term memory conditioning leads to the disappearance of anesthesia-resistant memory, another well-established form of consolidated memory. This finding contradicts the accepted models of memory consolidation in Drosophila and suggests that there are two forms of consolidated memory that are mutually exclusive.

  11. Through the Looking Glass?

    Cognitive development in humans takes a rather long time, but yields an apparently boundless and effortless variety of skills and flexible learning abilities. Disentangling this repertoire has been possible, in some cases, by studying the deficits produced by brain injury or disease. DeLoache et al. (p. 1027) have taken the approach of assessing the maturation of visuo-motor competency by observing errors of scale in children. Normally-developing young children were observed on occasion to attempt to perform actions that are impossible because of the extreme differences in the relative sizes of a child's body and a target object. For example, the child might attempt to sit on a doll's house chair or to wear a doll's clothes. This dissociation is consistent with dual-process theories that propose neurally and functionally distinct visual systems underlying perception and action.

  12. Controlling the Bacterial Cell Cycle

    Progression through the cell cycle requires the concerted action of a variety of protein regulators. Holtzendorff et al. (p. 983; published online 15 April 2004) have now identified a global cell cycle regulator, GcrA, in the bacterium Caulobacter crescentus. GcrA forms an oscillatory circuit with the previously known master regulator, CtrA. GcrA and CtrA directly regulate each other so that their concentrations oscillate out of phase temporally and spatially during the cell cycle to drive cell cycle progression and expression of polar differentiation factors.

  13. Concentrating After a Series of Moves

    Most techniques used to separate particles, including size exclusion chromatography and electrophoresis, suffer from resolution limits caused by particle dispersion. Even though these methods selectively change the path length of the migrating species, diffusion effects cause each particle to have its own path length. Huang et al. (p. 987) designed a fluidic channel with a series of posts, in which the gaps between posts is offset from one layer to the next, and where the rows of pillars are at a small angle relative to the flow direction. At high flow rates, particles that are small relative to the gap size zigzag through the posts, and overall take a path parallel to the flow direction. In contrast, larger particles are constantly driven toward one side of the channel in a staccato fashion. The separation appears to work both for hard and soft materials, and can also be used to concentrate particles within a solution.

  14. The Importance of Stretching

    For reactions of molecules with surfaces, the importance of how fast the molecule is moving normal to the surface (its translational kinetic energy) depends on how soon the reaction goes over the transition state to form products. If the barrier is “late,” that is, the transition state looks more like the products than the reactants, then translational energy can be less important than putting energy into vibrational modes. Smith et al. (p. 992) show that this nonstatistical situation occurs for the reaction of methane with the (111) surface of nickel. Putting energy in the ν 3 antisymmetric stretch was more effective for dissociating methane than putting the same amount of energy into increasing the molecule's velocity.

  15. Transcription, Chromatin Structure, and the Cell Cycle

    The conserved transcription factor TFIID is a multi-protein complex composed of the TATA binding protein (TBP) and multiple TBP-associated factors (TAFs). In Drosophila, the coactivator TAF1 contains two kinase domains; however, in vivo substrates for these kinase activities are unknown. Maile et al. (p. 1010) now show that the C-terminal region of TAF1 phosphorylates histone H2b at serine 33. Reducing the levels of TAF1 abolishes H2b phosphorylation, thereby reducing the transcription of an H2b- associated cell cycle regulator, and causes cell cycle arrest.