This Week in Science

Science  28 Jan 2011:
Vol. 331, Issue 6016, pp. 375
  1. Digesting Grass


      Identification of additional enzymes that can degrade cellulose efficiently should help in the development of biofuels on an industrial scale. Uncultured microorganisms living in cow rumen are highly effective at degrading plant cell walls. Hess et al. (p. 463) used metagenomics and single-genome sequencing to assemble draft genomes from microbes adhering to rumen-incubated switchgrass to identify nearly 28,000 genes related to known biomass-degrading families. Ninety candidate carbohydrate-degrading enzymes were synthesized and their activity analyzed against 10 different substrates, including the biofuel crops miscanthus and switchgrass. The data set greatly expands the repertoire of full-length genes available for use in industrial biotechnology.

    1. Nickels High and Low

        Certain transition metal complexes undergo a phenomenon termed spin crossover, in which a rise in temperature shifts the proportion of valence electrons that share the same spin orientation, and thus drive magnetic response. However, the collective shift across an ensemble of molecules in solution tends to be gradual and has been difficult to harness in switching applications such as contrast variation in magnetic resonance imaging. Venkataramani et al. (p. 445) present an alternative magnetic switching scheme, in which a photoresponsive ligand is used to modulate the electronic structure of a nickel complex. Isomerizations driven by different wavelengths of light selectively push the ligand onto or off the nickel ion, thereby inducing a high or low spin state. Up to 75% of the ensemble could thus be switched rapidly between magnetically active and passive states at room temperature.

      1. Ecology ↔ Evolution

          Ecology and evolution are fundamentally connected. ecological processes drive patterns of natural selection and thus shape evolutionary trajectories. The possibility that evolutionary change could also influence ecological processes is much less clear; it has often been assumed that evolutionary change takes too long to impact ecology. Schoener (p. 426) reviews how evolutionary change can in fact be extremely rapid, occurring over ecological time scales. Rapid evolutionary changes can thus give feedback on ecology and impact ecological processes such as population growth, community structure, and productivity.

        1. The Pneumococcus Game

            Pneumonia and meningitis caused by Streptococcus pneumoniae have accounted for millions of deaths through the ages. The Spanish strain is a globally occurring, multiply antibiotic-resistant lineage that has been exceptionally troublesome. Isolates of this lineage have been collected since 1984 from diverse geographic origins. Croucher et al. (p. 430, see the cover; see the Perspective by Enright and Spratt) have now used high-throughput sequencing technology to dissect serotype 23F's detailed evolution. The bacterium appears to respond to public health measures with extraordinary genetic agility, using a variety of recombination and base substitutions that can turn over three-quarters of the genome, enabling the pathogen to evade the effects of vaccines and antibiotics.

          1. Decoding a Childhood Cancer

              The identification of recurrent genetic changes in human tumors can provide important mechanistic insights into how tumors arise and, ideally, prompt new ideas for effective therapies. To date, this “cancer genomics” strategy has been applied only to adult cancers. Parsons et al. (p. 435, published online 16 December) now catalog the genetic alterations present in medulloblastoma, a brain tumor that mainly affects children. Interestingly, there were 5 to 10 times fewer genetic alterations in these tumors compared with solid tumors that typically affect adults. Among the most frequently mutated genes were two coding for enzymes that methylate histones, as well as genes affecting signaling pathways critical for normal brain development.

            1. Understanding Mysterious Order

                CREDIT: OKAZAKI ET AL.

                The heavy fermion compound URu2Si2 enters an ordered phase below 17.5 kelvin but, despite 25 years of extensive study, the exact nature of this phase remains a mystery. Using very pure, small specimens, Okazaki et al. (p. 439) found that the magnetic susceptibility in the ordered phase breaks the fourfold rotational symmetry of the URu2Si2 crystal, which suggests that the hidden order is an electronic nematic state.

              1. Laser Backfire

                  Standoff detection is an important method to monitor or probe regions that are otherwise inaccessible to direct sampling techniques. Dogariu et al. (p. 442) report the observation of high-gain infrared lasing in air from the focal region of an ultraviolet laser. The backward-directed infrared laser light could then be used as a remote spectroscopic tool that samples the air on its return path back to the sender position. The technique should find a range of applications—from the detection of greenhouse gas emissions and pollution to the detection of potentially hazardous and explosive materials.

                1. Reaction of Hydrogen Isotopes, Great and Small

                    Kinetic isotope effects reveal mechanistic insight into chemical reactions. Larger isotope ratios often lead to larger changes in rate, and, commonly, the largest ratio is 2—for the substitution of deuterium for hydrogen. Fleming et al. (p. 448; see the Perspective by Alexander) compared results for the simplest chemical reaction, of an H atom with H2, for two hydrogen isotopes created with positive and negative muons, which provide an unprecedentedly large mass ratio of 36. At 500 kelvin, the relative reaction rates measured agreed with those calculated using variational transition state theory.

                  1. Warmest in 2000 Years

                      Although the climate warming of the past century has occurred nearly everywhere, the Arctic shows the greatest temperature increase. Most of the heat transported to the Arctic comes from the Atlantic Ocean, which has warmed greatly over the past 150 years. How did the temperature of Arctic inflow from the Atlantic vary before anthropogenic climate warming began? Spielhagen et al. (p. 450) present a record of oceanic temperature variations for the last 2000 years, which shows that Atlantic water entering the Arctic through the Fram Strait is warmer than it has been in two millennia. This unprecedented warming is likely to represent a key factor in the apparent transition toward an ice-free Arctic Ocean.

                    1. Before the Mediterranean Exodus

                        Modern humans originated in Africa and then spread to Eurasia and beyond. The timing and locations of their emigration have been uncertain; genetic and archaeological data support an exodus along the Mediterranean by 60,000 years ago, but earlier attempts may have occurred, for example, in response to the massive Toba volcanic eruption about 75,000 years ago. Armitage et al. (p. 453; see the news story by Lawler) now describe artifacts from about 100,000 years ago found in eastern Arabia, indicating that modern humans were already there by then. This location would have allowed access to the Fertile Crescent and India as sea level dropped. The findings suggest that there may indeed have been an early exodus of modern humans from Africa.

                      1. Predatory Synergism

                          CREDIT: PIOVIA-SCOTT ET AL.

                          Synergies between species, in which the combined effect of multiple species is greater than the sum of their individual effects, link biodiversity to ecosystem function, but these synergies may be sensitive to external influences. Piovia-Scott et al. (p. 461) investigated how a synergy between two very different predator species in the Bahamas was affected by the influx of resources from the adjacent ocean. Adding seaweed to entire small islands (simulating the natural marine-to-terrestrial energy transfer that occurs during storms) eliminated the synergistic effect of two predators—lizards and ants—on arthropod herbivores and their food plants, increasing the overall rate of herbivory.

                        1. Parasite Replication Trigger

                            Apicomplexan parasites, including Toxoplasma gondii and the malaria parasite Plasmodium falciparum, actively invade host cells. Little is known about the signals that govern initiation of replication once the parasite is intracellular. Apical membrane antigen 1 (AMA1) is released onto the parasite surface during invasion and cleaved by intramembrane proteolysis, mediated by a rhomboid-like serine protease, ROM4. Santos et al. (p. 473, published online 23 December; see the Perspective by Cowman and Tonkin) used conditional expression of Toxoplasma ROM4 to show that ROM4 activity is not essential for invasion, but instead is required for subsequent replication of the intracellular parasite. Furthermore, transgenic expression of the cleaved cytoplasmic tail of AMA1 alone—either from the Toxoplasma AMA1 or from its P. falciparum ortholog—completely restored the replicative capacity of the intracellular parasites. Thus, intramembrane cleavage of AMA1 is required to trigger parasite replication within the host cell.

                          1. Bigger Beats Smaller

                              Social cooperation has been the subject of intense experimental investigation, both in humans and in other animals, and recent studies have detailed the developmental origins of these representations in human children and infants. Thomsen et al. (p. 477) now document the appearance of social dominance awareness in infants before the end of the first year. Infants were found to be capable of representing the conflicting goals of two cartoon characters, appearing to use size as a cue to predict which character will win.

                            1. So Hungry I Could Eat Myself

                                Autophagy is a process by which eukaryotic cells engulf and breakdown cellular components to provide new substrates for metabolism. Egan et al. (p. 456, published online 23 December; see the Perspective by Hardie) report a biochemical mechanism by which low energy stores in a cell can be linked to autophagy. The authors searched for targets of the adenosine monophosphate–activated protein kinase (AMPK), which is activated when cellular concentrations of adenosine triphosphate are depleted. AMPK was found to regulate another protein kinase, ULK1, which functions in regulation of autophagy. Cells engineered so that ULK1 could not be phosphorylated by AMPK failed to respond properly to starvation, had decreased autophagy, and were prone to starvation-induced cell death.

                              1. MALT Lymphomagenesis Revisited

                                  Mucosa-associated lymphoid tissue (MALT) lymphoma, a type of B cell lymphoma, is associated with chronic inflammation. Many patients are successfully treated with antibiotics; however, patients whose lymphomas express the API2-MALT1 fusion oncoprotein as a result of a chromosomal translocation are resistant to this therapy. API2-MALT1–driven lymphomagenesis is associated with deregulated canonical nuclear factor κB (NF-κB) signaling; however, Rosebeck et al. (p. 468) now demonstrate that noncanonical NF-κB signaling may also play a role. API2-MALT1, but not wildtype MALT1, cleaved the noncanonical NF-κB signaling intermediate, NF-κB–inducing kinase (NIK) driving constitutive noncanonical NF-κB signaling. API2-MALT1–expressing cells exhibited great resistance to apoptosis and enhanced integrin-mediated adhesion, both of which were NIK-dependent. Tumor samples from patients with API2-MALT1–expressing tumors expressed higher levels of noncanonical NF-κB genes compared with API2-MALT1–negative tumors. Thus, both canonical and noncanonical NF-κB signaling are likely to contribute to MALT lymphomagenesis.

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