American Scientist

In this roundup, digital features editor Katie L. Burke summarizes notable recent developments in scientific research, selected from reports compiled in the free electronic newsletter Sigma Xi SmartBrief. Online: https://www.smartbrief.com/sigmaxi/index.jsp

Smallest Life on Earth Discovered

Although the existence of ultrasmall bacteria was suspected, no microscopy or DNA had demonstrated their existence. Now they have been imaged by researchers at the US Department of Energy and the University of California, Berkeley, using a powerful cryogenic transmission electron microscope. The tiny bacteria have a volume of just 0.009 cubic microns—so small that 150 could fit inside a single Escherichia coli. Although they have densely packed spirals that appear to be DNA, as well as a small number of ribosome, the cells may rely on other microbes for some metabolic functions. These bacteria were found in groundwater and are thought to be diverse and common, belonging to three phyla that are poorly studied. The researchers next want to figure out what role the tiny organisms play in microbial communities and ecosystems, as well as what limits the function of the smallest living cells.

Luef, B., et al. Diverse uncultivated ultra-small bacterial cells in groundwater. Nature Communications doi:10.1038/ncomms7372 (February 27)

Ocean Vents on a Saturn Moon

A new study mounts evidence that Enceladus, one of Saturn’s 62 moons, has hydrothermal vents at the bottom of its ice-covered ocean—the first sign of such activity found outside Earth. Some leading theories posit that life emerged around such vents, so the presence of hydrothermal activity on another world is tantalizing. Although the vents cannot be observed directly, Sean Hsu of the University of Colorado, Boulder, and his team showed that silicon-rich dust ejected in plumes from Enceladus’s south pole could have formed only under specific thermal and chemical conditions. The researchers say that the silica must be leached from the moon’s core through hot seawater and then expelled toward the surface. A separate study also finds a surprising abundance of methane in the plumes, a possible (though far from certain) signature of biological activity.

Bouquet, A., O. Mousis, J. H. Waite, and S. Picaud. Possible evidence for a methane source in Enceladus’ ocean. Geophysical Research Letters doi:10.1002/14GL063013 (March 11)

Hsu, H.-W., et al. Ongoing hydrothermal activities within Enceladus. Nature 519:207 (March 12)

Malaria Infection and Blood Type

People with type O blood are less likely to die from severe malaria, but the reasons why have eluded researchers. The disease, which killed almost 600,000 people worldwide in 2013 according to the World Health Organization, is fatal when the malaria parasite causes red blood cells to stick to blood vessels, blocking blood flow. Mats Wahlgren of Karolinska Institutet in Sweden and his colleagues used data from experiments in cell culture and animals to show that the parasite secretes a protein called RIFIN that bonds to the surface of red blood cells, causing the cells’ fatal stickiness. The protein bonds much more readily with type A blood cells than with the chemically distinct type O. Understanding this mechanism is the first step toward developing a treatment.

Goel, S., et al. RIFINs are adhesins implicated in severe Plasmodium falciparum malaria. Nature Medicine doi:10.1038/nm.3812 (March 9)

Humans Appeared Earlier

Two new studies fill important gaps in knowledge of early hominins. A jawbone from Ethiopia, estimated to be 2.8 million years old, is the most ancient human fossil discovered yet; the previous record holders were 2.3- to 2.4-million-year-old Homo habilis fossils. A concomitant study of the sediment where the fossil was found showed that the environment at the time was more open and arid than once thought, a result consistent with the hypothesis that a climatic shift instigated the emergence of early humans. The researchers announcing the jawbone’s discovery think it is from a new species of Homo but are hoping to turn up more fossils before describing it. With an ape-like chin but human-like teeth, it exhibits a mix of primitive and modern features. Several recent discoveries have fueled the debate over how many species of early human there were.

DiMaggio, E. N., et al. Late Pleiocene fossiliferous sedimentary record and the environmental context of early Homo from Afar, Ethiopia. Science 347:1355 (Published online March 4)

Villmoare, B., et al. Early Homo at 2.8 Ma from Ledi-Geraru, Afar, Ethiopia. Science 347:1352 (Published online March 4)

Light Imaged as Wave & Particle

Physicists have long known that light acts as a particle and a wave, but for the first time they imaged both properties at once. A team led by Fabrizio Carbone of the École Polytechnique Fédérale de Lausanne shot laser light at a metallic nanowire, energizing its charged particles. Light traveled along the wire in two opposite directions. Where the waves of the light met from these two directions, it created a standing wave that could be visualized. The researchers simultaneously shot a stream of electrons at the nanowire that made the light speed up or slow down. Using an ultrafast microscope, the position of these changes in speed could be imaged, appearing as an exchange of energy, or quanta, between electrons and photons. The quanta demonstrated the particle-like nature of light; the standing wave demonstrated its wave-like property. This development not only contributes to theory but also provides new ways of studying quantum computing.

Piazza, L., et al. Simultaneous observation of the quantization and the interference pattern of a plasmonic near-field. Nature Communications doi:10.1038/ncomms7407 (March 2)