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This Week in PNAS: Sep 30, 2014

In the early, online edition of the Proceedings of the National Academy of Sciences, researchers from the University of Washington and elsewhere present findings from an effort to trace the evolution of mutualism between two microbes: the sulfate-reducing bacteria Desulfovibrio vulgaris and the hydrogenotrophic methanogen archaea Methanococcus maripaludis. By applying metagenomic sequencing and other assessments to samples collected during the first 1,000 generations after D. vulgaris and M. maripaludis bugs were combined, the team was tracked the loss of certain functions in each as mutualism evolved. After only a few dozen generations of being introduced to M. maripaludis, for example, D. vulgaris tended to take on mutations that interfered with its ability to respire on sulfate, making it less adept at surviving independently.

An international team led by investigators in France retraced the role of captured retroviral sequences called syncytins in mammalian placentation using existing genome sequences and quantitative RT-PCR testing in hedgehog tenrecs. When they searched for syncytins in the early-diverging tenrec lineage with data from greater and lesser hedgehog tenrecs from Madagascar and mainland Africa, the researchers detected placenta-specific expression of an apparent syncytin dubbed syncytin-Ten1, consistent with a long-standing role for such genes in placental function. "We proposed that such genes have been pivotal for the emergence of placental mammals from egg-laying animals and should be present all along the Placentalia radiation," the researchers write.

Finally, a team based in the US ad Sweden describes a fluid-like state for DNA that they detected by single-molecule and pooled calorimetric testing on a bacteria-infecting virus. The phage, known for infecting Escherichia coli cells in the human gut, contains tightly compacted DNA that can be rapidly ejected from its capsid, the researchers explain. Their results suggest that this feat is achieved due to a solid-to-fluid-like change in the molecular material at normal human body temperatures. "Our finding shows a remarkable physical adaptation of bacterial viruses to the environment of Escherichia coli cells in a human host," the group writes.