“Exploring Phages Abroad: An In-Depth Study by MIT News”

MIT Graduate Student Discovers New Way Bacteria Protect Themselves Against Phages

For the past two and a half years, graduate student Tong Zhang has been researching phages and bacteria, exploring their constant arms race known as the Red Queen Conflict. Phages and bacteria are in a never-ending cycle of adaptation and co-evolution, where both the infectee and the infectant are forced to continually adapt to the other.

Restriction Modification Systems

One of the best-known anti-phage defense systems is known as restriction modification systems. This influential system was studied and developed by Salvador Luria, an MIT professor and the founding director of what is known today as the Koch Institute for Integrative Cancer Research. The anti-phage defense system can distinguish between self-DNA and foreign DNA, and are always active, scanning for foreign DNA to protect the host.

Other Anti-Phage Systems

While researchers have characterized systems that protect bacteria from phages, many questions remain about how those systems become activated during infection.

Activation of toxin-antitoxin system CapRel

In a paper published in 2021, Tong Zhang and her collaborating team found that during phage infection, the capsid protein that coats the outside of the phage directly triggers activation of a toxin-antitoxin system called CapRel. This CapRel system includes a C-terminal domain that works as an infection sensor and an inhibitor of the toxic N-terminus. Capsid proteins of phages infecting Escherichia coli bind to the C-terminal domain, activating the toxic N-terminus defense system and blocking phage replication. Before Tong’s paper, it was unclear that phage proteins could directly activate this defense system.

Navigating the Challenges of Research and Education

Despite the pandemic causing academic and personal challenges, Tong Zhang and her team worked diligently on the CapRel project. Although it has been over three years since she last visited her home in Beijing, Tong stays driven and motivated to succeed. Zhang is currently hard at work on her next project, with “cool data” already in-hand, according to her supervisor Laub.

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