The genetic prehistory of southern Africa

Southern and eastern African populations that speak non-Bantu languages with click consonants are known to harbour some of the most ancient genetic lineages in humans, but their relationships are poorly understood. Here, we report data from 23 populations analyzed at over half a million single nucleotide polymorphisms, using a genome-wide array designed for studying human history. The southern African Khoisan fall into two genetic groups, loosely corresponding to the northwestern and southeastern Kalahari, which we show separated within the last 30,000 years. We find that all individuals derive at least a few percent of their genomes from admixture with non-Khoisan populations that began approximately 1,200 years ago. In addition, the east African Hadza and Sandawe derive a fraction of their ancestry from admixture with a population related to the Khoisan, supporting the hypothesis of an ancient link between southern and eastern AfricaComment: To appear in Nature Communication

Two Major Medicinal Honeys Have Different Mechanisms of Bactericidal Activity

Honey is increasingly valued for its antibacterial activity, but knowledge regarding the mechanism of action is still incomplete. We assessed the bactericidal activity and mechanism of action of Revamil® source (RS) honey and manuka honey, the sources of two major medical-grade honeys. RS honey killed Bacillus subtilis, Escherichia coli and Pseudomonas aeruginosa within 2 hours, whereas manuka honey had such rapid activity only against B. subtilis. After 24 hours of incubation, both honeys killed all tested bacteria, including methicillin-resistant Staphylococcus aureus, but manuka honey retained activity up to higher dilutions than RS honey. Bee defensin-1 and H2O2 were the major factors involved in rapid bactericidal activity of RS honey. These factors were absent in manuka honey, but this honey contained 44-fold higher concentrations of methylglyoxal than RS honey. Methylglyoxal was a major bactericidal factor in manuka honey, but after neutralization of this compound manuka honey retained bactericidal activity due to several unknown factors. RS and manuka honey have highly distinct compositions of bactericidal factors, resulting in large differences in bactericidal activity

Long time-lapse nanoscopy with spontaneously blinking membrane probes

Imaging cellular structures and organelles in living cells by long time-lapse super-resolution microscopy is challenging, as it requires dense labeling, bright and highly photostable dyes, and non-toxic conditions. We introduce a set of high-density, environment-sensitive (HIDE) membrane probes, based on the membrane-permeable silicon-rhodamine dye HMSiR, that assemble in situ and enable long time-lapse, live-cell nanoscopy of discrete cellular structures and organelles with high spatiotemporal resolution. HIDE-enabled nanoscopy movies span tens of minutes, whereas movies obtained with labeled proteins span tens of seconds. Our data reveal 2D dynamics of the mitochondria, plasma membrane and filopodia, and the 2D and 3D dynamics of the endoplasmic reticulum, in living cells. HIDE probes also facilitate acquisition of live-cell, two-color, super-resolution images, expanding the utility of nanoscopy to visualize dynamic processes and structures in living cells