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PNAS Looks at Emerging Songbird Pathogen, More

A University of Exeter-led team considers potential interactions between pathogen virulence, bacterial replication rate, and host resistance. In particular, the researchers focused on Mycoplasma gallisepticum, an emerging songbird pathogen in North America that jumped from poultry to house finch hosts. After introducing 55 M. gallisepticum isolates into 55 previously unexposed wild American house finches from Arizona that were confirmed to be infection-free with PCR testing and other approaches, they tracked bacterial load, symptom severity, and mortality rates in the birds, along with bacterial replication rates and more. Based on their results, the authors suggest that "pathogen virulence and replication rates can evolve independently, particularly after the initial spread of host resistance."

Harvard researchers report on findings from a CRISPR-Cas9-based gene editing knockdown screen done in the human pathogen Vibrio cholerae. The team systematically knocked out predicted-essential V. cholerae genes, uncovering decreased viability for forms of the bug missing more than three dozen independent genes, including the components of the lipoprotein transport pathway. Through a series of follow-up experiments, the investigators saw hints that diminished lipoprotein transport has downstream effects on V. cholerae outer membrane organization and plasmolysis susceptibility. "Our work generates mechanistic insights into fundamental areas of V. cholerae biology," the investigators say, "with important implications for medical prevention of devastating cholera outbreaks."

A team from Germany, the Netherlands, and elsewhere describe a deeply diverged form of the hepatitis B virus (HBV) found in shrews, insect-eating animals from a lineage that split off early in mammalian evolution. Through PCR-based screening on almost 700 shrews from Sorex and Crocidura genera in Europe and Africa, the researchers tracked down 17 HBV-carrying shrews, using nested PCR assays, phylogenetics, and cell line experiments, and other approaches to characterize the HBV genomes, place them within a broader HBV tree, and explore their functional capabilities. "The phylogenetically divergent shrew HBVs comprise separate species termed crowned shrew HBV and musk shrew HBV, each containing distinct genotypes," the authors write, noting that features found in the shrew HBVs "corroborated ancient origins of mammalian HBVs dating back about 80 million years."