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The management of stillbirth: coping with an unreality.
With about 1 stillbirth occurring in every 80 deliveries, stillbirth is a common tragedy. Yet it is an event which, by common consent, is cloaked in secrecy, and which by its very nature seems unreal. There are thus strong forces operating on the bereaved mother and her family, and on the professionals who care for them, to keep the crisis of stillbirth hidden away, therby in fact hindering the mourning and healing process. Bourne has produced statistical evidence to show that family docotrs are astonishingly reluctant to know or remember anything about the patient who has had a stillbirth. I would like to put forward some suggestions for helping doctors to overcome their reluctance to face the problem of stillbirth.
Filamentous cheater phages drive bacterial and phage populations to lower fitness.
Many bacteria carry phage genome(s) in their chromosome, which intertwines the fitness of the bacterium and the phage. Most Pseudomonas aeruginosa strains carry filamentous phages called Pf that establish chronic infections and do not require host lysis to spread. However, spontaneous mutations in the Pf repressor gene (pf5r) can allow extreme phage production that slows bacterial growth and increases cell death, violating an apparent détente between bacterium and phage. We observed this paradoxical outcome in an evolution experiment with P. aeruginosa in media simulating nutrients from the cystic fibrosis airway. Bacteria containing pf5r mutant phage grow to a lower density but directly outcompete their ancestor and convert them into pf5r mutants via phage superinfection. Reduced fitness therefore spreads throughout the bacterial population, driven by weaponized Pf. Yet high intracellular phage replication facilitates another evolutionary conflict: "cheater miniphages" lacking capsid genes and the superinfection exclusion gene (pfsE) invade populations of full-length phages within cells. Although bacteria containing both full-length phages and miniphages are most immune to superinfection by limiting the Pf receptor, this hybrid vigor is extremely unstable, as a classic Tragedy of the Commons scenario ensues that causes complete prophage loss. The entire cycle - from phage hyperactivation to miniphage invasion to prophage loss - can occur within 24h, showcasing rapid coevolution between bacteria and their filamentous phages. This study demonstrates that P. aeruginosa, and potentially many other bacterial species that carry filamentous prophages, risk being exploited by these phages in a runaway process that reduces fitness of both host and virus.
Cooperation, competition and enforcement in transposon evolution.
Transposons are powerful drivers of genome evolution, but we lack a clear understanding of how these selfish genetic elements evolve and co-evolve with their hosts. Here, we develop a new general model of transposon-host co-evolution that incorporates key details of transposon and host biology. Our model reveals that the way that transposons replicate is critical for their evolutionary prognosis. Publicly-replicating transposons (such as DNA transposons), which cooperatively share their replication machinery, are predicted to be self-limiting. However, privately-replicating transposons (such as long interspersed nuclear elements, or LINEs), which do not replicate cooperatively, are under continual selection to increase their duplication rate even to the point of host extinction, a so-called tragedy of the commons. Neither selection against transposons' deleterious effects nor exploitation by parasitic elements is sufficient to prevent host extinction. Instead, our analysis shows that only active suppression by hosts avoids population collapse. In particular, suppression must act post-transcriptionally in order to prevent continuous escalation of the transposon-host genetic conflict. We argue that only with host enforcement of transposons can complex life exist.
Seveso: the tragedy lingers on.
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Seveso: the tragedy lingers on.
Explore the source record for details and available documents.