This Week in Science

Science  16 Apr 2021:
Vol. 372, Issue 6539, pp. 250
  1. Fire Ecology

    Carbon cycling after boreal forest fire

    1. Andrew M. Sugden

    A burned black spruce forest in Alaska quickly recovers, with deciduous species dominating after fires that burn deep.

    PHOTO: MICHELLE C. MACK

    Wildfire activity has been increasing in the boreal forests of the Northern Hemisphere, releasing carbon into the atmosphere from biomass and soil, with potential feedback to climate warming. In a long-term study, Mack et al. analyzed wildfire impacts on the carbon balance of boreal forest in Alaska, with particular focus on forest-regeneration patterns. After fire, the species composition in most of the study sites changed from black spruce to a mixture of conifers and deciduous broadleaf tree species. The stands that had shifted to deciduous dominance stored fivefold more soil carbon than stands that returned to black spruce dominance. Therefore, the functional traits of deciduous trees compensated for the combustion loss of soil carbon, pointing to a potential mitigation of the feedback effect of boreal forest fire to climate warming.

    Science, this issue p. 280

  2. Paleontology

    Estimating dinosaur abundance

    1. Sacha Vignieri

    Estimating the abundance of a species is a common practice for extant species and can reveal many aspects of its ecology, evolution, and threat level. Estimating abundance for species that are extinct, especially those long extinct, is a much trickier endeavor. Marshall et al. used a relationship established between body size and population density in extant species to estimate traits such as density, distribution, total biomass, and species persistence for one of the best-known dinosaurs, Tyrannosaurus rex, revealing previously hidden aspects of its population ecology.

    Science, this issue p. 284

  3. Signal Transduction

    Circuit design for control of metabolism

    1. L. Bryan Ray

    A transcriptional control mechanism in yeast that allows cells to respond to changes in nutrient concentrations works very much like a household light-dimmer switch. That is, the system separately controls whether gene expression is “on” or “off” and the extent of gene expression. The galactose-responsive pathway is activated when yeast need to switch from metabolizing glucose to metabolizing galactose. Ricci-Tam et al. found that, rather than using two separate elements for the switch and dimmer controls, yeast use a single transcription factor, Gal4p, separately regulating its abundance (through transcriptional regulation) and its catalytic activity (through interaction with a protein-binding partner). Such regulation may be common and can allow responses to the environment on physiological and evolutionary time scales.

    Science, this issue p. 292

  4. Membranes

    One-step purification and desalination

    1. Marc S. Lavine

    The purification of water for drinking purposes can require multiple filtration steps and technologies to remove contaminants such as salts and heavy metals. Some contaminants could have value if recovered, but these are often discharged in the waste streams. Uliana et al. describe a general approach for the fabrication of robust, tunable, adsorptive membranes through the incorporation of porous aromatic framework (PAF) nanoparticles into ion exchange membranes such as those made from sulfonated polymers. Salts are removed using a series of cation and anion exchange membranes, and the PAF particles can be selected to capture specific target ions, such as those of copper, mercury, or iron. This allows for simultaneous desalination and decontamination of the water.

    Science, this issue p. 296

  5. Quantum Networks

    A three-node quantum network

    1. Ian S. Osborne

    Future quantum networks will provide the means to develop truly secure communication channels and will have applications in many other quantum-based technologies. Pompili et al. present a three-node remote quantum network based on solid-state spin qubits (nitrogen-vacancy centers in diamond) coupled by photons. The implementation of two quantum protocols on the network. entanglement distribution and entanglement swapping, illustrates a key platform for exploring, testing, and developing multinode quantum networks and quantum protocols.

    Science, this issue p. 259

  6. 2D Materials

    Twisted and nematic

    1. Jelena Stajic

    Electrons in quantum materials can break rotational symmetry even when the underlying crystal lattice does not. This phenomenon, called nematicity, has been observed in many unconventional superconductors. Cao et al. found that magic-angle twisted bilayer graphene, in which superconductivity was recently discovered, also exhibits nematicity. The breaking of rotational symmetry was observed through transport measurements, which exhibited characteristic anisotropy.

    Science, this issue p. 264

  7. Tumor Immunology

    Sequence of immunotherapy matters

    1. Dan A. Erkes

    Immune checkpoint blockade is clinically successful in various cancer types, yet many treated patients relapse. Determining effective combination therapies that induce systemic antitumor immunity is crucial. Immune checkpoint blockade combined with local radiation can improve antitumor responses, but it remains unclear how the sequence of these therapies alters efficacy. Wei et al. used mouse tumor models to demonstrate that treatment with anti–PD-1 after stereotactic body radiation therapy (SBRT) elicited superior systemic antitumor immunity, abscopal effects, and protection compared with anti–PD-1 given before SBRT. These data were correlated with improved intratumoral CD8+ T cell responses and decreased CD8+ T cell death in local and distant tumors. This work provides preclinical rationale for giving anti–PD-1 after SBRT in patients with cancer.

    Sci. Immunol. 6, eabg0117 (2021).

  8. Imaging

    Pathogen-specific PET

    1. Caitlin Czajka

    Enterobacterales infections can affect diverse locations within the body, and multidrug-resistant strains are difficult to diagnose and treat. Ordonez et al. used an 18F-labeled sugar alcohol as a bacteria-specific imaging agent to detect and monitor infections in patients. Positron emission tomography (PET)/computerized tomography imaging showed selective uptake of the tracer in Enterobacterales infections as opposed to other types of inflammation or cancer. Signal was reduced in sites of drug-susceptible infections in patients after treatment with antibiotics. The authors also showed that the imaging agent could differentiate bacterial infection from severe acute respiratory syndrome coronavirus 2 in a hamster model, supporting its use for bacteria-specific imaging.

    Sci. Transl. Med. 13, eabe9805 (2021)

  9. Quantum Computing

    Combatting noise on the platform

    1. Phil Szuromi

    The potential of quantum computers to solve problems that are intractable for classical computers has driven advances in hardware fabrication. In practice, the main challenge in realizing quantum computers is that general, many-particle quantum states are highly sensitive to noise, which inevitably causes errors in quantum algorithms. Some noise sources are inherent to the current materials platforms. de Leon et al. review some of the materials challenges for five platforms for quantum computers and propose directions for their solution.

    Science, this issue p. eabb2823

  10. Microbial Genomics

    Mining wild animal microbiomes

    1. Laura M. Zahn

    We have only just begun to examine the multitude of bacteria associated with other organisms. Levin et al. sampled the feces of 184 wild animals, including fish, birds, and mammals, from four different continents to survey the diversity of gut bacteria (see the Perspective by Lind and Pollard). They discovered more than 1000 previously undescribed bacterial species and identified factors that correlate with the composition, diversity, and functional content of the microbiota. Supporting the association of specific bacteria with animal lifestyle, they identified proteases, some previously undescribed, from the gut of griffon vultures that can break down toxins that may be present in their carrion diet.

    Science, this issue p. eabb5352; see also p. 238

  11. Neuroscience

    Recording many neurons for a long time

    1. Peter Stern

    The ultimate aim of chronic recordings is to sample from the same neuron over days and weeks. However, this goal has been difficult to achieve for large populations of neurons. Steinmetz et al. describe the development and testing of Neuropixels 2.0. This new electrophysiological recording tool is a miniaturized, high-density probe for both acute and long-term experiments combined with sophisticated software algorithms for fully automatic post hoc computational stabilization. The technique also provides a strategy for extending the number of recorded sites beyond the number of available recording channels. In freely moving animals, extremely large numbers of individual neurons could thus be followed and tracked with the same probe for weeks and occasionally months.

    Science, this issue p. eabf4588

  12. Neurodevelopment

    More is not always better

    1. Pamela J. Hines

    Mutations in X-linked genes usually affect male individuals more than females, but the opposite characterizes the Protocadherin-19 gene (PCDH19) on the X chromosome. Mutations in the PCDH19 cell-adhesion molecule cause cognitive impairment, affecting females more than males. Hoshina et al. studied mice with PCDH19 mutations, showing that a mismatch between PCDH19 and another cell-adhesion molecule causes trouble when mossy fibers of the brain are forming synapses (see the Perspective by Shohayeb and Cooper). In the heterozygous setting, mutant PCDG19 sequesters the partner cell-adhesion molecule into dysfunctional complexes. In the hemizygous setting, as in males, enough of that partner cell-adhesion molecule roams free to make functional interactions.

    Science, this issue p. eaaz3893; see also p. 235

  13. Coronavirus

    Patterns and bottlenecks

    1. Caroline Ash

    A year into the severe acute respiratory syndrome coronavirus 2 pandemic, we are experiencing waves of new variants emerging. Some of these variants have worrying functional implications, such as increased transmissibility or antibody treatment escape. Lythgoe et al. have undertaken in-depth sequencing of more than 1000 hospital patients' isolates to find out how the virus is mutating within individuals. Overall, there seem to be consistent and reproducible patterns of within-host virus diversity. The authors observed only one or two variants in most samples, but a few carried many variants. Although the evidence indicates strong purifying selection, including in the spike protein responsible for viral entry, the authors also saw evidence for transmission clusters associated with households and other possible superspreader events. After transmission, most variants fizzled out, but occasionally some initiated ongoing transmission and wider dissemination.

    Science, this issue p. eabg0821

  14. Gut Physiology

    Goblet cell diversity

    1. Caroline Ash

    An adult human has a gut surface area averaging 30 square meters that is bombarded daily by xenobiotics and microorganisms. Mucus synthesized by goblet cells supplies a protective barrier coating. Nyström et al. discovered that goblet cells are not all the same along the length of the gut; rather, they form different functional populations depending on location. Small-intestine mucus is laced with antimicrobial peptides and is permeable to small molecules; downstream, thicker mucus is generated that excludes bacteria and xenobiotics. Mucus oozes in thick plumes from goblet cells within the crypts to shield the stem cell niche. Between the crypts lie highly differentiated goblet cells producing permeable mucus. Together, both types of mucus form a network that shelters the gut epithelium. If, however, the intercrypt goblet cells become dysfunctional, the exposed epithelium is exposed to bacteria and vulnerable to developing colitis.

    Science, this issue p. eabb1590

  15. Quantum Simulation

    A minimal Weyl semimetal

    1. Jelena Stajic

    Many compounds have now been identified as Weyl semimetals, materials with an unusual electronic band structure characterized by the so-called Weyl points. Weyl points always appear in pairs, but the solid-state materials studied so far have at least four. Wang et al. engineered a Weyl semimetallic state with the minimum number of Weyl points (two) in a gas of ultracold atoms trapped in an optical lattice (see the Perspective by Goldman and Yefsah). To do that, the researchers had to create three-dimensional spin-orbit coupling in this system. The relative simplicity of the resulting band structure will make it easier to observe the unusual effects associated with this state.

    Science, this issue p. 271; see also p. 234

  16. Paleontology

    Paleontology for conservation

    1. Sacha Vignieri

    Human activities are leading to broad species and system declines. Prevention of such declines has led us to focus on either protection for species or protection for ecosystem function. Looking at past patterns of species and system change can help to inform our understanding of the long-term impacts of these strategies. Blanco et al. studied mammals from the last 21 million years on the Iberian Peninsula, finding long periods of functional stasis, even in the face of taxonomic variability (see the Perspective by Roopnarine and Banker). Functional ecosystems were more resistant to ecosystem collapse.

    Science, this issue p. 300; see also p. 237

  17. Magnetism

    A gapped spin liquid

    1. Jelena Stajic

    Quantum spin liquids avoid conventional magnetic ordering down to the lowest temperatures. Among the candidates for this state of matter, organic salts such as κ-(BEDT-TTF)2Cu2(CN)3 have been prominent. Miksch et al. studied this material using electron spin resonance to elucidate the nature of its ground state. Instead of the expected gapless state, the temperature dependence of spin susceptibility suggests the formation of a spin gap.

    Science, this issue p. 276

  18. Ocean Microbiology

    Genomes reveal nutrient stress patterns

    1. Michael A. Funk

    Within the surface ocean, nitrogen, iron, and phosphorous can all be limiting nutrients for phytoplankton depending on location. Ustick et al. used the prevalence of Prochlorococcus genes involved in nutrient acquisition to develop maps of inferred nutrient stress across the global ocean (see the Perspective by Coleman). They found broad patterns of limitation consistent with an Earth system model and nutrient addition experiments. Leveraging metagenomic data in this manner is an appealing approach that will help to expand our understanding of the biogeochemistry in the vast open ocean.

    Science, this issue p. 287; see also p. 239

  19. Kinases

    mTORC2 marks kinases for maturity

    1. Wei Wong

    The activity of AGC family kinases such as Akt and protein kinase C (PKC) requires multiple phosphorylation events at different sites. Baffi et al. identified an evolutionarily conserved motif in Akt and PKC called the target of rapamycin (TOR) interaction motif (TIM), the phosphorylation of which by the kinase TOR in the mammalian target of rapamycin complex 2 (mTORC2) was required for activation. Phosphorylation of the PKC TIM by mTORC2 abolished the dimerization of newly synthesized PKC, ultimately leading to full activity. These results highlight a potential negative effect of TOR kinase inhibitors that are currently in clinical development.

    Sci. Signal. 14, eabe4509 (2021).

  20. Materials Science

    Changing the balance

    1. Joseph C. Prestigiacomo

    Compensated semimetals feature unusual material properties and exotic quantum states of matter that are mediated by an equal number of positive and negative charge carriers. Chatterjee et al. discovered that the balance of carriers in lutetium antimonide (LuSb) can be tuned by confining them to ultrathin epitaxial films, showing that positively charged holes disappear as the film thickness is reduced to a few monolayers. A novel two-dimensional hole gas was also observed at the interface of the films when bond mismatched to a semiconducting gallium antimonide substrate. Using this approach, the authors have provided insights into the origin of the nonsaturating magnetoresistance in semimetallic LuSb.

    Sci. Adv. 10.1126/sciadv.abe8971 (2021).

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