The bacterial cells that normally colonize our bowels can be distinguished from other bacterial species by using what is traditionally considered their enemy: a virus. Researchers report on April 16 in the magazine. Cellular reports that some bacteria use viruses that have infected them (ie, phages) for self-recognition and, therefore, show greater physical fitness, repelling competitors that lack this adaptation.
"This is the first evidence that cells can be distinguished from related competitors by using a virus," says Thomas Wood, of Pennsylvania State University, one of the co-senior authors of the study. "The implications are that we must reevaluate the relationship between a virus and its cellular host, since sometimes there are benefits of having a viral infection."
The idea for the study began when Wood and his team noticed a line of demarcation that was formed between different strains of Escherichia coli K-12, but not between identical clones, since they swam with each other. To investigate the underlying mechanisms, Wood, the first author Sooyeon Song of the Pennsylvania State University, and the study's lead author, Xiaoxue Wang, of the Chinese Academy of Sciences, analyzed the behavior of swimming around the world. E. coli K-12 library of 4,296 knockouts of a single gene.
They discovered that the demarcation line disappeared completely only because of a mutation that affects a gene that is required for the replication of some phages. The findings suggest that proteins related to phages are responsible for bacterial self-recognition.
According to this idea, the researchers found that the demarcation line was also eliminated by E. coli Strain K-12 lacks the nine cryptic prophages: bacteriophage genomes that have integrated into bacterial chromosomes but do not form active phage particles or break ("lyse") their host cells. In particular, additional experiments revealed that the cryptic prophage CPS-53 and one of its proteins, YfdM, were necessary for the demarcation line.
Since CPS-53 is essentially inactive in terms of cell lysis and production of phage particles, the researchers suspected that the demarcation line is formed through cell lysis caused by a different active phage. They found that exposure of bacterial cells containing an active lytic phage called SW1 to YfdM stimulated the production of phage particles and caused the lysis of cells, mainly those lacking SW1. Higher concentrations of YfdM or phage particles produced thicker demarcation lines between bacterial cells. The findings suggest that SW1 controls the formation of the demarcation line by using one of the host cryptic prophage proteins, YfdM of CPS-53, to propagate.
"E. coli he uses the tools of his old enemy, which got stuck on his chromosome, to work with this new SW1 virus, which is mainly kept outside the cell, basically navigating the cell, "says Wood. So the bacterial cell is both using a new virus, SW1, against its competitors and using a protein from a virus that it attacked millions of years ago. "
This strategy clearly benefited the host cells, which repelled other strains lacking SW1 and showed a growth advantage when challenged with phage particles from other strains. "The cell uses a new virus, SW1, and an ancient virus protein, YfdM, as tools for the search for food, and all bacteria usually starve," says Wood. "The basic idea is that the cell that carries the SW1 virus does not die as much as the one that the SW1 virus has not seen before, so the cell that carries the SW1 virus is more suitable than the cell that lacks the virus."
This newly discovered mechanism of self-recognition allows bacteria to form social groups, cooperating with relatives while antagonizing non-relatives during behaviors that may be important for feeding, virulence, protection, quorum detection and biofilm formation . "It's often thought that bacteria live individually, but they can actually feed in groups," says Wood. "To act as a group, they must be able to distinguish themselves from other bacteria." In a type of social activity, when they communicate, bacterial cells secrete chemical signals to communicate, we now show that cells use viruses to distinguish closely related bacteria.
In future studies, the researchers plan to investigate how SW1 avoids attacking its host cells, instead killing mainly the bacteria lacking the virus. Ultimately, understanding how cells compete may be useful for synthetic biology applications that mimic nature and use bacteria in groups. "Also, if we understand better how viruses choose which cells to attack, we may be in a better position to use viruses to fight bacterial infections."
Biologists turn viruses from illegal eavesdropping into bacterial killers.
Cellular reports, Song et al .: "Phages Mediate Bacterial Self-Recognition" https://www.cell.com/cell-reports/fulltext/S2211-1247(19)30400-0, DOI: 10.1016 / j.celrep.2019.03. 070
Bacteria take advantage of viruses to distinguish friend from enemy (2019, April 16)
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