Lately gut microbiota scientists have been paying more attention to phages—bacterial viruses—in the gut environment, to uncover how they interact with bacteria to affect activities in the gut.
Temperate phages—those that enter bacterial genomes in a dormant (prophage) state—are present in most strains of bacteria. Generally, by incorporating into the host bacterium, these temperate phages are thought to increase host fitness by supplying beneficial genes.
In a recent study in PLOS Genetics, investigators wanted to know the impact of prophage carriage in the gastrointestinal tract of monoxenic mice. They studied Escherichia coli bacteria paired with phage λ (both wild-type and mutant strains).
According to the results, carrying the phage had a fitness cost to the bacterial host because of a significant increase in the prophage induction rate (responding to a signal like DNA damage). But this changed when the bacteria were in competition with other bacteria. When prophage-carrying bacteria were competing with isogenic phage-susceptible bacteria, the prophage indirectly helped its host by killing competitors.
Authors say this study is the first quantitative characterization of interactions between temperate phages and bacteria in a simplified gut environment (i.e. mice colonized with only one bacterial species). It shows that taking prophages into account is important when researchers study the actions of specific bacteria in the mammalian gastrointestinal tract. In the future, scientists will find out more about how phages interact with bacteria and how they impact the overall activities of the gut microbiota. Possibly, say the authors, the gut could be a hotspot for bacterial evolution through its high temperate phage activity.
Phages could also be key actors in ecological regulation of microbiota composition, with most acute relevance in perinatal microbiota establishment, as well as during intake of bioactive microbes preventatively or therapeutically.
De Paepe M, Tournier L, Moncaut E, Son O, Langella P, Petit M-A (2016) Carriage of λ Latent Virus Is Costly for Its Bacterial Host due to Frequent Reactivation in Monoxenic Mouse Intestine. PLoS Genetics 12(2): e1005861. doi: 10.1371/journal.pgen.1005861