From polymer physics to quicker commuter travel
Optimized traffic on the London Underground. The size of each node and the thickness of each edge are proportional to the traffic through them.
Whether planning water distribution routes, military convoy movements, internet traffic, or simply the best way to the airport, path optimization algorithms are essential for everyday logistics. Global optimization techniques that consider all path choices simultaneously are computationally difficult. As a result, most existing routing algorithms choose paths individually, but these methods tend to favor the shortest path regardless of the choice’s impact on other routes. Chi Ho Yeung et al. (pp. 13717–13722) have borrowed from the physics of polymers to create a simple, generic, and distributed global path optimizing algorithm. The researchers tested their statistical physics-based technique on large real-world data sets, including the London Underground subway system and global air traffic. Compared to current methods, the algorithm decreased overall congestion at the cost of a slightly longer path length. The algorithm worked best with intermediate traffic densities, where optimization is particularly difficult. In addition to solving common optimization problems, the authors suggest that the technique may also reveal properties of optimal routing scenarios that are otherwise difficult to uncover. — J.M.
Wisdom of crowds put to the test
Group of house-hunting ants. Image courtesy of James S. Waters (Department of Ecology and Evolutionary Biology, Princeton University, Princeton).
Researchers have long recognized the advantages of collective intelligence during the performance of goal-oriented tasks by social animals. To determine whether individual insight might outweigh collective intelligence under certain circumstances, Takao Sasaki et al. (pp. 13769–13773) trained Temnothorax ants, known for their house-hunting skills, to choose the better of two nest sites under conditions of varying quality, represented by the level of the site’s interior brightness. The authors report that when the qualitative differences between alternative nest site choices were small, colonies were more likely than individual ants to choose the better of two nest sites. In contrast, when the qualitative differences between the choices were large, individuals outperformed colonies in choosing the better site, suggesting that the wisdom of crowds might be more advantageous for difficult perception and discrimination tasks than for easy ones. Using a mathematical model, the authors found that positive feedback between colony members can help colonies integrate information and outperform individuals in tasks that require the perception of subtle differences. However, such a feedback mechanism might lead colonies to make suboptimal choices during the performance of relatively easy perception tasks. According to the authors, the findings help determine the conditions under which individual judgment and collective decision making might be selectively applied. — P.N.
Tracing genomic evolution of H. pylori
About half of the human population harbors stomach infections caused by the bacterium Helicobacter pylori, and these infections have been implicated in a variety of health problems, including 1 in 20 human cancers. Epidemiologic studies suggest H. pylori may be transmitted orally, or via an fecal-oral route, between family members but it remains unclear how the organism’s genome evolves and recombines over time within the confines of close family. Xavier Didelot et al. (pp. 13880–13885) performed whole genome comparisons of 97 H. pylori isolates obtained from 52 members of two families living in rural South Africa. The authors analyzed within-host evolution of the H. pylori genome by comparing strains isolated from two areas of the stomach, the antrum and corpus, and uncovered evidence of multiple H. pylori infections in at least five family members. Multiple infections significantly increased the organism’s genomic recombination rate compared with single infections, the authors report. An analysis of transmission patterns between family members revealed that while H. pylori was more frequently spread to close relatives and household members than to others, most individuals in the study were not infected by other family members. According to the authors, the findings have important implications for the evolution and epidemiology of H. pylori. — A.G.
Molecular basis for the effects of an herbal supplement
Reishi mushrooms. Image courtesy of Eric Steinert (Paussac, France)/Wikipedia.
Polysaccharides found in herbal supplements such as the Reishi mushroom (Ganoderma lucidum) have long been believed to boost innate immunity, but the mechanisms underlying the biomolecules’ beneficial effects have remained unclear. Shih-Fen Liao et al. (pp. 13809–13814) previously found that F3, a crude extract of fucose-containing polysaccharides from the Reishi mushroom, likely interacts with various immune receptors on mammalian cells, bolsters immunity, and helps fight tumors. Extending their findings, the authors report that immunization with F3 slowed the growth of lung cancer cells in a mouse model and prolonged the animals’ survival in a dose-dependent manner. F3 did not directly affect tumor cell viability, suggesting an indirect, immune-mediated mechanism of action. The authors used chromatography to isolate a fucose-enriched fraction of F3 called FMS and characterized the fraction’s effect on tumor-associated molecules called Globo H-series glycans. They found that the fraction triggered the production of IgM antibodies against Globo H and related molecules by B1 immune cells in immunized mice. Further, the authors found that the terminal fucose residue on FMS is crucial to its immunogenicity, and the biochemical backbone of FMS likely underpins the antitumor activity of its protective IgM antibodies. According to the authors, the findings uncover a molecular basis for the immune-mediated antitumor activity of Reishi mushroom polysaccharides. — P.N.
Ion channel implicated in sunburn pain
UVB generates sunburn pain by activating epidermal TRPV4.
Overexposure to UVB radiation causes sunburn-related tissue damage and pain, but the precise molecular mechanism underlying sunburn pain remains unclear. Carlene Moore et al. (pp. E3225–E3234) tested whether a cation-conducting channel called TRPV4, found on epithelial skin cells and skin-innervating neurons and previously implicated in physiological pain, might be involved in sunburn pain. The authors report that mice with engineered deletions in the Trpv4 gene in keratinocytes were less sensitive to thermal and mechanical stimuli after UVB exposure, compared with mice without the deletions; the level of the gene’s knockdown corresponded to the sensitivity to sunburn pain. Further, the authors demonstrated that epidermal TRPV4 is essential for the tissue-injury response to UVB in the skin of mice, and that a signaling molecule called endothelin-1 likely mediates the response. In addition, the authors found that a topical small-molecule inhibitor that selectively blocks TRPV4 reduced endothelin-1 levels, epidermal tissue damage, and UVB-induced pain in mice. More importantly, TRPV4 and endothelin-1 levels were increased in the epidermis of patients with sunburn and UV overexposure, compared with healthy human skin, suggesting that the ion channel might play a crucial role in human skin’s response to damaging UV radiation. According to the authors, selective TRPV4-inhibitors might be suitable candidates for the development of topical agents for attenuating sunburn-related tissue damage and pain. — P.N.