WASHINGTON – The Editorial Board of the Proceedings of the National Academy of Sciences (PNAS) has selected six papers published by PNAS in 2019 to receive the Cozzarelli Prize, an award that recognizes outstanding contributions to the scientific disciplines represented by the National Academy of Sciences (NAS). Papers were chosen from the more than 3,300 research articles that appeared in the journal last year and represent the six broadly defined classes under which the NAS is organized.

The annual Cozzarelli Prize acknowledges papers that reflect scientific excellence and originality. The award was established in 2005 as the Paper of the Year Prize and was renamed in 2007 to honor late PNAS Editor-in-Chief Nicholas R. Cozzarelli. The 2019 awards will be presented at the PNAS Editorial Board Meeting, and awardees will be recognized at an awards ceremony during the NAS Annual Meeting in Washington, DC.

2019 Cozzarelli Prize Recipients

Class I: Physical and Mathematical Sciences

"The end of ice I," by Daniel R. Moberg, Daniel Becker, Christoph W. Dierking, Florian Zurheide, Bernhard Bandow, Udo Buck, Arpa Hudait, Valeria Molinero, Francesco Paesani, and Thomas Zeuch

What is the minimum number of water molecules needed to form a stable ice crystal? To answer this question, Moberg et al. used infrared spectroscopic measurements of slow-cooled water droplets and molecular dynamics simulations. The authors identified the existence of ice in clusters of as few as 90 water molecules. The authors further determined that in clusters of fewer than 150 molecules, the equilibrium between ice and liquid occurs through oscillation of the clusters between crystalline and liquid phases. The results provide insight into the behavior of water under nanoscale confinement, which may occur in proteins and other materials.

Accompanying commentary: https://www.pnas.org/content/116/49/24383

Class II: Biological Sciences

"Mosaic origin of the eukaryotic kinetochore," by Eelco C. Tromer, Jolien J. E. van Hooff, Geert J. P. L. Kops, and Berend Snel

When eukaryotic cells evolved from prokaryotic ancestors, they vastly increased in complexity. How many of the typical eukaryotic features emerged during this process remains unclear. Tromer, van Hooff, et al. reconstructed the origin of one such feature, the kinetochore, a large proteinaceous structure that drives separation of chromosomes during cell division. The authors found that the proteins that make up the kinetochore are of mosaic origin: Some have relatives in different eukaryotic or prokaryotic cellular processes, whereas others are unique to the kinetochore. Nevertheless, many kinetochore proteins share part of their evolutionary trajectories, arising from ancient gene duplications within the kinetochore. The results suggest that the kinetochore originated by recruiting proteins globally and expanded by duplicating them locally, characterizing one of the modes by which key eukaryotic systems evolved.

Accompanying commentary: https://www.pnas.org/content/116/26/12596

Class III: Engineering and Applied Sciences

"Mechanics unlocks the morphogenetic puzzle of interlocking bivalved shells," by Derek E. Moulton, Alain Goriely, and Régis Chirat

Two groups of animals—brachiopods and bivalve mollusks—sport interlocking shells that help guard against predators and environmental perturbations. Each group is thought to have independently evolved bipartite shells more than 540 million years ago from a common ancestor lacking shells, and the two halves of each shell are secreted by distinct lobes of a membranous organ called the mantle. Moulton et al. used a mathematical model of shell growth to determine how the shell valves interlock tidily despite being formed separately. Seamless interlocking, the authors report, is a consequence of the geometry and physics of shell growth: Mechanical instability arising from the interaction of the soft mantle with the rigid shell edge and from the interaction between the mantle lobes results in a perfectly interlocking pattern. Moreover, the findings explain how fine-tuning the shell growth process produces the striking diversity of forms seen in shells.

Class IV: Biomedical Sciences

"Widespread soil bacterium that oxidizes atmospheric methane," by Alexander T. Tveit, Anne Grethe Hestnes, Serina L. Robinson, Arno Schintlmeister, Svetlana N. Dedysh, Nico Jehmlich, Martin von Bergen, Craig Herbold, Michael Wagner, Andreas Richter, and Mette M. Svenning

Atmospheric methane is a major contributor to global warming. Methane-oxidizing bacteria are an important biological sink for atmospheric methane, but no pure cultures of such microbes have been available. Tveit, Hestnes, et al. isolated a pure culture of a methane-oxidizing soil bacterium that can grow on air. The strain, which the authors named Methylocapsa gorgona MG08, oxidizes methane at atmospheric concentrations for use as a carbon and energy source. The strain is also capable of using carbon dioxide, carbon monoxide, dinitrogen, dioxygen, and hydrogen for energy conservation or biomass synthesis. The findings suggest that some microbes can satisfy their needs for energy, carbon, and nitrogen by relying solely on air.

Class V: Behavioral and Social Sciences

"Bioarchaeology of Neolithic Çatalhöyük reveals fundamental transitions in health, mobility, and lifestyle in early farmers," by Clark Spencer Larsen, Christopher J. Knüsel, Scott D. Haddow, Marin A. Pilloud, Marco Milella, Joshua W. Sadvari, Jessica Pearson, Christopher B. Ruff, Evan M. Garofalo, Emmy Bocaege, Barbara J. Betz, Irene Dori, and Bonnie Glencross

The human transition from foraging to farming began 10,000–11,000 years ago in Southwest Asia. To determine the impact of the transition on human lifestyle, health, and culture, Larsen et al. conducted a bioarchaeological investigation at Çatalhöyük (7100–5950 cal BCE), a large Neolithic site in south-central Turkey that was continuously inhabited for 1,150 years. Building on earlier investigations, the authors analyzed the influence of the environment, diet, and living circumstances on human health and well-being at this early farming settlement. The authors found that the transition to farming led to higher birth rates, which in turn led to crowded living conditions. Such conditions contributed to increased labor demands, risk of interpersonal violence, and exposure to disease, presaging similar changes in living conditions in settlements elsewhere. The study provides rich insights into human lifestyle changes wrought by early agriculture.

Accompanying commentary: https://www.pnas.org/content/116/28/13721

Class VI: Applied Biological, Agricultural, and Environmental Sciences 

"Economics of the disintegration of the Greenland ice sheet," by William Nordhaus

Concerns about impacts on large-scale earth systems have become pertinent to the scientific analysis of climate change. While the impacts are likely to be significant, there has been little work integrating the geophysical and economic aspects of the potential disintegration of the Greenland ice sheet (GIS). Nordhaus developed a model that integrated the economics and geophysics of the GIS to investigate melt paths that would occur under different climate policies. Weak climate policies would lead to ice-sheet melting beyond a threshold known as the Robinson upper tipping point, after which rebuilding is extremely slow even if warming reverses. Conversely, strong climate policies would stop GIS disintegration before melting reaches critical tipping points. The author notes that adding the damages from GIS disintegration contributes less than 5% to the social cost of carbon, or the price of emissions in a market context, because the slow melt rate puts damages into the distant future.

Accompanying commentary: https://www.pnas.org/content/116/25/12134

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