Editors' Choice

Science  16 Sep 2011:
Vol. 333, Issue 6049, pp. 1551
  1. Microbiology

    Light Interception

    1. Caroline Ash
    CREDIT: AGSTOCKUSA/ALAMY

    Aside from humankind's special demands, the Sun supplies most of the energy needed by marine and terrestrial organisms. Photosynthesis in leafy plants occurs via chlorophyll pigments, but many aquatic microorganisms can detect and capture sunlight with rhodopsin pigments. The surface of leaves, which is known as the phyllosphere, is an important habitat for pigmented microorganisms. Atamna-Ishmaeel et al. asked whether leaf-colonizing microorganisms, which in the total phyllosphere are estimated to number 1026, compete with or complement their supporting plants' ability to harvest light. In a metagenomic survey of a variety of wild plants, 156 microbial rhodopsin sequences were found, a quarter or more of which seemed to be sensory, and others energy-capturing, proton pumps. Moreover, all of the phyllosphere rhodopsins had the amino acid leucine at position 105 in the protein, indicating that they absorbed green light. In contrast, this position is occupied by glutamine in the marine rhodopsin-bearing microbes, and the pigment consequently absorbs blue light. This means that the phyllosphere microbes are unlikely to compete with their host plant's chlorophyll, but whether this complementarity is a signature of a mutualism is an open question.

    Environ. Microbiol. 13, 10.1111/j.1462-2920.2011.02554.x. (2011).

  2. Cell Signaling

    Getting the Message

    1. L. Bryan Ray

    Cells have a limited number of biochemical signaling pathways and thus have to use the same pathway to produce strikingly different biological outcomes. Andreu-Pérez et al. report a mechanism that allows cultured PC-12 cells (derived from rat brain cells) to respond to epidermal growth factor (EGF) by proliferating, but to respond to nerve growth factor (NGF) by differentiating. Both growth factors activate a cascade of protein kinases that begins with the protein kinase Raf and ends with activation of extracellular signal–regulated protein kinases (ERKs). The authors' results indicate that, in response to EGF, the strength and duration of signaling through ERKs are limited because the enzyme protein arginine-methyltransferase 5 (PRMT5) is activated and methylates Raf proteins, causing them to be more rapidly degraded in the cell. These events were missing in cells treated with NGF, in which PRMT5 was not activated. If methylation of Raf proteins was blocked by inactivation of PRMT5 or by expression of a Raf protein engineered to lack a site for methylation, EGF in fact created stronger, more prolonged signaling through ERK that produced differentiation rather than proliferation. Thus, protein methylation is another mechanism by which signaling pathways can be modulated to produce different outcomes.

    Sci. Signal. 4, ra58 (2011).

  3. Materials Science

    Tuning Plasmons

    1. Phil Szuromi

    Shifts in localized surface plasmon resonances (LSPRs) are often associated with analytical techniques—for example, monitoring the adsorption of molecules on gold thin films. Semiconductor nanoparticles can also exhibit LSPRs that can be tuned with changes in composition. Indium tin oxide (ITO) nanoparticles are transparent at visible wavelengths but can have LSPRs at near-infrared wavelengths. Garcia et al. were able to tune the LSPR of thin films of tin-doped ITO nanoparticles. The as-synthesized nanoparticles were coated with oleic acid, which would inhibit electrical contact between them, but after thin films were deposited, the coating was exchanged with formic acid. This thinner coating enabled electrochemical doping that could shift the LSPR to render previously transparent films strongly absorbing in the near-infrared. The authors suggest that such effects could be useful for controlling thermal transport in applications such as smart windows.

    Nano Lett. 11, 10.1021/nl202597n (2011).

  4. Microbiology

    Inside Job

    1. Caroline Ash

    Most plants only thrive in intimate associations with fungi—or arbuscular mycorrhizal (AM) fungi—and engage in mutualistic nutrient exchange with the plant. Some AM fungi have recently been discovered to have their own bacterial symbionts. Ghignone et al. have explored the genome of a newly discovered species of rod-shaped endobacterium that lives within vacuoles of the Gigaspora margarita AM fungus. The genome sequence of the endobacterium shows that it is unable to degrade starch or sugars, unlike the fungus, and indeed has a limited ability to import sugars from its host. What it can do, though, is obtain energy by breaking down amino acids extracted from fungal oligopeptides—and to alleviate this parasitism, the endobacterium has the capacity to synthesize vitamin B12 and thus potentially to donate this nutrient to its fungal host. This is not the symbiont's only trick, because, like the pathogen Salmonella, the bacterium possesses the genes for the syringe-like type III secretion system, by which means it may inject various effectors across the vacuole wall. This genome offers another glimpse into the nested interdependencies we are beginning to expect to see when we observe microorganisms closely.

    ISME J. 5, 10.1038/ismej.2011.110 (2011).

  5. Physics

    Spectroscopy on the Move

    1. Ian S. Osborne
    CREDIT: SINCLAIR ET AL., PHYS. REV. LETT. 107, 93002 (2011)

    Spectroscopy looks at the transitions between quantum mechanical energy levels in atoms, ions, and molecules. Matching the transition frequencies to the corresponding elemental structures is at the heart of chemical detection techniques to identify and distinguish compounds. The ultrahigh precision with which the transitions can be measured also provides a platform to test fundamental theories of physics by probing possible changes in the fundamental physical constants. Frequency combs—broadband spectra of light comprising precisely spaced “teeth” of extremely narrow linewidth—have revolutionized spectroscopy, allowing transitions to be picked out with great sensitivity. For applications in astronomy, however, such as identifying the chemical species in distant galaxies, the absorptions and emissions associated with particular transitions are affected by the Doppler shift, a consequence of the expanding universe that can complicate chemical assignment. As compensation, velocity modulation spectroscopy can be used to mimic the redshift of the retreating distant astronomical objects, but resolution has tended to be limited. Sinclair et al. have combined the precision of frequency combs with velocity modulation spectroscopy and thereby expanded the frontiers of high-resolution spectroscopy for astrophysical observations.

    Phys. Rev. Lett. 107, 93002 (2011).

  6. Psychology

    Damned with Feint Phrase

    1. Gilbert Chin

    The exponential growth of Facebook users reveals how humans thirst for social information, constantly seeking opinions voiced by friends about others, whether they are mutual friends or public figures. Psychological research has distilled much of social perception into the orthogonal dimensions of warmth and competence; furthermore, a halo effect—whereby holistic positive or negative judgments of people influence how they are rated on individual factors—has been widely reported. Kervyn et al. now show that a different pattern can emerge. When faced with a decision to welcome or rebuff an applicant to a travel tour or a workforce, subjects rated “outgoing” candidates lower on competence and “hard-working” candidates lower on warmth than generically positive applicants. That is, omitting information about one dimension, regardless of its saliency for the type of social grouping under consideration, resulted in negative inferences, which in turn led to a higher likelihood of rejection.

    J. Exp. Soc. Psychol. 47, 10.1016/j/jesp.2011.08.001 (2011).

  7. Astronomy

    Signs of the Sun's Passage

    1. Maria Cruz

    Recent models of the evolution of our galaxy suggest that the Sun's radial position in the Milky Way has changed during its history; in particular, the Sun may have formed closer to the galactic center, where stellar densities were higher, and then migrated outward to its current position. Through numerical simulations, Kaib et al. analyzed how the migration of the Sun through more crowded galactic environments would have affected the architecture of the Oort Cloud, the vast reservoir of icy bodies that surrounds the solar system from whence long-period comets are believed to come. Because of its location at the very edge of the solar system, the Oort Cloud's dynamics are highly sensitive to stellar and galactic gravitational perturbations. These would have been much stronger if the Sun were once deeper in the galaxy and would have affected the location of the inner edge of the Oort Cloud. A closer inner edge in the past may explain the unusual orbit of the trans-Neptunian dwarf planet Sedna, which is well beyond those of the giant planets and the Kuiper Belt (the other reservoir of comets, just beyond the orbit of Neptune) but inside the current inner edge of the Oort Cloud.

    Icarus 10.1016/j.icarus.2011.07.037 (2011).

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