Shapiro redux: bacterial phage defences (Introduction)

by David Turell , Thursday, January 11, 2024, 18:17 (106 days ago) @ David Turell

They use a specific molecular module against the phage:

https://phys.org/news/2024-01-reveals-unexpected-strategy-competition-bacteria.html

"Understanding how Gabija and other elements of bacterial defense systems look and work—along with the mechanisms that viruses known as phages use to overcome these defenses and infect bacteria—promises to illuminate broader aspects of immunity, including human immunity and immune responses to cancer.

"Already, the team has revealed an unexpected strategy that phages might use to neutralize Gabija in the evolutionary arms race between bacteria and phages.

"'This is the importance of basic science," said Kranzusch, senior author of the paper. "We're learning how cells defend against infection."

"Gabija is one of hundreds of defense systems found in bacteria. It is present in about 15% of all bacteria whose genes have been sequenced.

"'It's one of the most prevalent bacterial defense systems," said Antine, who is first author of the study. "Yet very little was known about how it works or how viruses that infect bacteria can evade the system."

***

"Gabija, she learned, is a very large complex. It is about one-quarter the size of the ribosome, which is a huge molecular machine that performs the incredible task of using information from RNA to make proteins.

"Antine also learned that Gabija is formed using the instructions from just two genes, GajA and GajB. GajA forms proteins that connect in groups of four to form the center of the structure. GajB forms proteins that connect to form the outer winglike portions of the structure.

***

"It isn't yet clear how this large complex recognizes and defeats the phage. But Antine and Kranzusch suspect that the complex recognizes a specific structure formed by phage DNA and then degrades it.

"'Gabija has exquisitely evolved to hunt and destroy a very particular target," said Kranzusch.

***

"...she found that the phage evolved DNA that encodes a very large protein that surrounds Gabija and inactivates it.

""The protein forms this huge web around the entire outside of the complex," said Kranzusch. "This evasion technique creates a massive complex. It was a surprising result that changes the way we think about how phages interact with these defense systems."

"Phages are often thought of as small and simple, but Kranzusch has found that that's not always true. The phages he and Antine are studying are large, with DNA that holds hundreds of genes.

"Phages are also considered entities rather than living organisms because they require a host cell to replicate. Yet they actively evolve and change under pressure from defense systems like Gabija.

"'They are complex and can evolve and adapt with their host. They shape evolution," said Kranzusch.

"For next steps, Antine will dive into the precise mechanisms Gabija uses to defeat phages. These mechanisms are the result each side finding new ways to defeat the other. The same kind of one-upmanship goes on in cancer, as tumor cells find increasingly clever ways to evade the immune system and cancer treatments.

"'There are parallels between immunity in human cells and in bacteria," says Antine. "We're interested in the diversity, the many ways that immune systems combat something that is actively evolving against it."

Comment: it seems cancer cells, phages and bacteria all can edit DNA. And humans are now editing DNA. The appearance of multicellularity has removed that ability in those organisms' cells.