The price of efficiency
Procreating many offspring is costly to most organisms. Because what the production of offspring consumes in terms of energy, the parents will later lack to live on. This dilemma apparently also applies to viruses.
Longevity and successful reproduction should actually complement each other splendidly from an evolutionary point of view: if you live long, you father many children. In practice, however, both goals in life are mostly opposed to each other. Because where only limited endogenous resources are available, each organism must carefully consider what it uses them for. A compromise would be the ideal solution, according to the life cycle theory: Every being should bring just enough offspring into the world so that there is still enough energy left to enjoy the old age.
Now neither the concept of twilight nor the expression of offspring is appropriate for a bacteriophage. Because it does not have its own metabolism, but uses its bacterial host to transform its genetic material into new viruses, some biologists simply deny its existence as a living being. But despite its uncertain status, a phage's life follows different cycles: it assembles, breaks out of the host, injects its genome into a new victim, and thus creates new phages with the help of the host. Even death is familiar to phages: If they don't find a new host for a certain period of time, they become inactive - the virulent cycle is broken.
The cause of this "phage death" has not yet been fully clarified. However, the end of the virus will probably come with a bang: the capsid, the protein shell of the virion, ruptures and parts of the genetic material it contains escapes. But why and under what circumstances this protein shell ruptures has so far been little researched. A French research team has now taken on the further search for the cause - and came to interesting results.
The geneticists Marianne De Paepe and Francois Taddei from the University of Paris used 16 different coliphage strains as guinea pigs. These viruses specialize in the bacterium Escherichia coli, but differ in their virulence and in the number of progeny produced per host bacterium. De Paepe and Taddei then distributed the different phage strains on the host medium and then compared the number of newly produced viruses with the number of coliphages that had become inactive over time over a period of 60 days.
Interestingly, those strains that produced a greater number of phages per infested host had a higher mortality rate. The more efficiently they knew how to use their host's resources, the more likely it was that they would only "survive" briefly outside the bacterium.
At the same time, the scientists discovered two possible causes of premature death within the phage blueprint: if the viruses contained very densely packed DNA, they showed a higher mortality rate than strains whose genetic material was less compressed. The scientists explain this with the intracellular pressure that can arise from the DNA structure. This could also explain why those phages that only had a thin capsid wall became inactive more frequently and more quickly.
Researchers cannot yet pinpoint exactly how reproductive rate is related to coliphage instability. However, they suspect that the energetic and kinetic processes that lead to a high or low reproduction rate of the phages have a direct influence on the structure and thus the probability of survival of the viruses. It is not only one's own resources that have to be invested wisely: one should not be overly generous with someone else's genetic material either. Because mass alone does not necessarily ensure survival.
