American Scientist

In this roundup, Katie Burke summarizes notable recent items about scientific research, selected from news reports compiled in the free electronic newsletter Sigma Xi SmartBrief.

Fungal Jungle

Human feet—specifically, the heel, toenail and toe web—have the highest fungal diversity of all skin regions, with approximately 80 different fungal genera. Comparing fungal diversity from 14 body sites in 10 different people, researchers sequenced fungal DNA and also grew 130 fungal strains in culture. The most abundant fungus found on skin was the dandruff-associated genus Malessezia. Parts of the body that had low fungal diversity (2–10 species) included the chest and abdomen. Bacteria seem to have different bodily preferences than fungi. The greatest bacterial diversity in this study was observed on people’s arms. One person in the study had recently been treated with oral antifungal medication and also exhibited a particularly diverse fungal community. The researchers suggested that this unusual fungal mix indicated an imbalance that could be associated either with the fungal disease or with the antifungal treatment. They proposed that such skin microbiota comparisons could be used to develop novel probiotic treatments for skin fungus imbalances that could circumvent the undesirable side effects that some antifungal medications pose.

Findley, K., et al. Topographic diversity of fungal and bacterial communities in human skin. Nature (Published online May 22)

Elementary!

Five familiar elements in the middle of the periodic table—bromine, magnesium, germanium, indium and mercury—just had their atomic weights updated. Atomic weight is based on the number of protons and neutrons in an atom’s nucleus. The amount of protons does not vary, but the quantity of neutrons does. Atoms of the same element (with the same number of protons) with different numbers of neutrons are called isotopes. Some isotopes are unstable and undergo radioactive decay. Others are stable. For example, bromine has two stable isotopes, and magnesium has three. Because of their multiple stable isotopes, all of which are relatively abundant on Earth, the International Union of Pure and Applied Chemistry decided to express these elements’ atomic weights with intervals that encompassed their multiple stable isotopes. Two years ago, the IUPAC changed other common elements’ atomic weights to intervals, and more elements’ atomic weights may receive similar scrutiny in the future.

Wieser, M. E., et al. Atomic weights of the elements 2011 (IUPAC Technical Report). Pure and Applied Chemistry 85:1047–1078 (April 29)

Ladybirds Gone Wild

An Asian ladybird beetle, the harlequin ladybird (Harmonia axyridis) is an invasive insect that may be an all too familiar and unwelcome guest in your home. Originally introduced to control aphids in agriculture, populations of the pest have exploded in abundance, outcompeting or even eating native ladybird species. A recent study suggests that the invasive ladybird’s success may be partially due to hosting a single-celled parasite. This parasite is virulent to native ladybirds, such as the seven-spot ladybird (Coccinella septempunctata), but does not harm the invasive ladybird. The parasite may be transmitted when native ladybirds eat harlequin ladybird eggs, or when parasitic wasps lay their eggs across multiple ladybird species. Several other hypotheses have been put forward to explain the widespread success of the harlequin ladybird at the expense of native species. How much this particular disease is affecting population dynamics has yet to be determined.

Vilcinskas, A., K. Stoecker, H. Schmidtberg, C. R. Röhrich and H. Vogel. Invasive harlequin ladybird carries biological weapons against native competitors. Science 340:862–863 (Published May 17)

In Its Prime

A major breakthrough has been made on a proof that has stumped mathematicians since 1849. A prime number is divisible only by 1 and itself. Some primes come in pairs, meaning they are only two numbers apart—for example, 3 and 5, 5 and 7, or 11 and 13. They are aptly called twin primes. The twin prime conjecture states that there are an infinite number of these twin primes, but a proof has never been completed successfully. To make matters more complicated, at larger and larger numbers, the distances between prime numbers also tend to be larger. Mathematicians have been working on a related question to help them tackle the twin prime conjecture proof: Are there infinite prime numbers that are separated by a particular set distance that is larger than two? Recently, Yitang Zhang of University of New Hampshire declared that the answer was yes: An infinite number of prime numbers is separated by a finite distance of at most 70 million.

Zhang, Y. Bounded gaps between primes. Annals of Mathematics (Accepted May 21)

Worldly Frogs

Chytrid fungus, which causes the disease chytridiomycosis in amphibians, is considered the biggest threat to worldwide amphibian diversity because it has caused multiple population declines and extinctions. For example, the extinction of several species of harlequin frog (genus Atelopus) in Central America and the endangering of the mountain yellow-legged frog (Rana muscosa) in California are attributed to chytrid fungus pandemics. A new study of the disease’s origins suggests that the spread of a nonnative frog species introduced through international trade for pets and research, the African clawed frog (Xenopus laevis), is linked to disease outbreaks in California. Previous studies had documented that populations of this species in Africa carried the disease, but this new study is the first to document populations in the United States that carry the disease.

Vredenburg, V. T., et al. Prevalence of Batrachochytrium dendrobatidis in Xenopus collected in Africa (1871-2000) and in California (2001-2010). PLoS ONE 8:e63791 (May 15)