In the study published yesterday in Nature Microbiology, a team from the University of Otago discusses how phages hide from bacterial defenses. Specifically they describe the discovery of a Serratia jumbo phage that is not recognized by CRISPR-Cas defenses that would normally cut up the genetic DNA instructions to make many new phages.
The team had molecular and genetic evidence for what was happening, but really needed to see directly inside these tiny bacteria. By using a spinning disk confocal microscope, "when phages infected the bacteria, we could see their DNA was encased by a physical 'shield' and hidden from the CRISPR-Cas defence systems that couldn't gain access," co-author Laura Gumy explained.
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However, to take over the host, the phages must produce RNA messages that leave this protective compartment. "This is the Achilles heel of these phages and can be destroyed by a special group of CRISPR-Cas defenses that recognize RNA messages," first author, Lucia Malone added.
According to the team, the study broadens the knowledge of phage-host interactions and demonstrates that "jumbo" phages are less susceptible to bacterial defense systems than some other phages. In addition, the study provides new insights into how phages evade bacterial defense systems, which could help advance the use of phages as anti-bacterials.