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The cystic fibrosis (CF) respiratory tract harbors pathogenic bacteria that cause life-threatening chronic infections. Of these, Pseudomonas aeruginosa becomes increasingly dominant with age and is associated with worsening lung function and declining microbial diversity. We aimed to understand why P. aeruginosa dominates over other pathogens to cause worsening disease. Here, we show that P. aeruginosa responds to dynamic changes in iron concentration, often associated with viral infection and pulmonary exacerbations, to become more competitive via expression of the TseT toxic effector. However, this behavior can be therapeutically targeted using the iron chelator deferiprone to block TseT expression and competition. Overall, we find that iron concentration and TseT expression significantly correlate with microbial diversity in the respiratory tract of people with CF. These findings improve our understanding of how P. aeruginosa becomes increasingly dominant with age in people with CF and provide a therapeutically targetable pathway to help prevent this shift., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2023 The Authors. Published by Elsevier Inc. All rights reserved.)

Pseudomonas aeruginosa infections can be difficult to treat and new therapeutics are needed. Bacteriophage therapy is a promising alternative to traditional antibiotics, but large numbers of isolated and characterized phages are lacking. We collected 23 diverse P . aeruginosa isolates from people with cystic fibrosis (CF) and clinical infections, and used them to screen and isolate over a dozen P . aeruginosa -targeting phages from hospital wastewater. Phages were characterized with genome sequencing, comparative genomics, and lytic activity screening against all 23 bacterial host isolates. We evolved bacterial mutants that were resistant to phage infection for four different phages, and used genome sequencing and functional analysis to study them further. We also tested phages for their ability to kill P . aeruginosa grown in biofilms in vitro and ex vivo on CF airway epithelial cells. Overall, this study demonstrates how systematic genomic and phenotypic characterization can be deployed to develop bacteriophages as precision antibiotics., Competing Interests: J.B. is a consultant for BiomX, Inc. The other authors declare no competing interests., (© 2022 The Author(s).)

Pseudomonas aeruginosa notoriously adapts to the airways of people with cystic fibrosis (CF), yet how infection-site biogeography and associated evolutionary processes vary as lifelong infections progress remains unclear. Here we test the hypothesis that early adaptations promoting aggregation influence evolutionary-genetic trajectories by examining longitudinal P. aeruginosa from the sinuses of six adults with CF. Highly host-adapted lineages harbored mutator genotypes displaying signatures of early genome degradation associated with recent host restriction. Using an advanced imaging technique (MiPACT-HCR [microbial identification after passive clarity technique]), we find population structure tracks with genome degradation, with the most host-adapted, genome-degraded P. aeruginosa (the mutators) residing in small, sparse aggregates. We propose that following initial adaptive evolution in larger populations under strong selection for aggregation, P. aeruginosa persists in small, fragmented populations that experience stronger effects of genetic drift. These conditions enrich for mutators and promote degenerative genome evolution. Our findings underscore the importance of infection-site biogeography to pathogen evolution., Competing Interests: Declaration of interests V.S.C. is a founder of Microbial Genome Sequencing Center, LLC (MiGS) and is a scientific advisor for MiGS., (Copyright © 2021 The Authors. Published by Elsevier Inc. All rights reserved.)

How the microbiome and mucosal environment mediate homeostatic immunity in the skin is not well understood. In this issue of Cell, Lima-Junior and colleagues report that skin commensal bacteria induce endogenous retrovirus (ERV) expression and antiviral immune responses in keratinocytes, favoring the priming of beneficial commensal-specific T cell subsets that promote tissue homeostasis., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Extracellular vesicles (EVs) are increasingly appreciated as a mechanism of communication among cells that contribute to many physiological processes. Although EVs can promote either antiviral or proviral effects during viral infections, the role of EVs in virus-associated polymicrobial infections remains poorly defined. We report that EVs secreted from airway epithelial cells during respiratory viral infection promote secondary bacterial growth, including biofilm biogenesis, by Pseudomonas aeruginosa. Respiratory syncytial virus (RSV) increases the release of the host iron-binding protein transferrin on the extravesicular face of EVs, which interact with P. aeruginosa biofilms to transfer the nutrient iron and promote bacterial biofilm growth. Vesicular delivery of iron by transferrin more efficiently promotes P. aeruginosa biofilm growth than soluble holo-transferrin delivered alone. Our findings indicate that EVs are a nutrient source for secondary bacterial infections in the airways during viral infection and offer evidence of transkingdom communication in the setting of polymicrobial infections., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2021 The Author(s). Published by Elsevier Inc. All rights reserved.)

Extracellular DNA is an important component of the biofilm matrix. Now, Pseudomonas aeruginosa is shown to control autolysis through the production of HQNO, a quorum-sensing-regulated respiratory poison. Thus, HQNO-driven autolysis links programmed cell death with quorum sensing and biofilm formation., (Copyright © 2016 Elsevier Ltd. All rights reserved.)