Researchers from Pennsylvania State University and elsewhere used comparative genomics to characterize a so-called "super-shedder" strain of Escherichia coli — work they describe in PLOS One. After sequencing the genome of the E. coli O157 strain SS17, the team compared it with existing E. coli sequences, determining that SS17 shares features with a hyper-virulent O157 subgroup that clusters with E. coli linked to spinach-borne outbreaks. But SS17 had several variants that distinguished it from other E. coli strains, too, including polymorphisms suspected of boosting the bug's ability to adhere to epithelial cells in the bovine rectum — a feature suspected of contributing to its elevated transmission by cattle.
In PLOS Biology, an international group led by investigators in the UK explores evolutionary relationships between Piwi-interacting small RNAs and other small RNAs using small RNA sequence data for Caenorhabditis elegans and 10 other nematode species. Through small RNA sequencing on these nematodes, the researchers found piRNAs present in C. elegans and its close relatives, but missing in other nematode lineages. In the absence of piRNAs, they note, one of two mechanisms RNA-dependent RNA polymerase activity-based mechanisms seem step in to take up the slack. The findings "highlight the rapid, context-dependent evolution of small RNA pathways," authors of the study say, "and suggest piRNAs in animals may have replaced an ancient eukaryotic RNA-dependent RNA polymerase pathway to control transposable elements."
A team from Germany and the UK consider the genetic forces at play during divergence in parapatric stickleback populations with distinct parasite susceptibility patterns from five different lake or river locales. As they report in PLOS Genetics, the researchers used genome sequence data for 60 three-spined stickleback representatives from these sites to assess the source and extent of heterogeneity found in divergent portions of the genome. Their results revealed a combination of selection, "hitchhiking" at sites neighboring those under positive selection, and local gene flow reductions in divergent genome regions.