horizontal gene transfer:viral DNA transfer in gut infection (Introduction)

by David Turell , Friday, March 17, 2017, 14:01 (2587 days ago) @ David Turell

A very clear-cut study showing how viruses that live in bacteria (bacteriophages) play a major role during gut infections by bacteria:

http://www.the-scientist.com/?articles.view/articleNo/48833/title/Inflammation-Drives-G...

"Intestinal inflammation caused by Salmonella infection activates bacteriophages within the bacteria to spread genes throughout the colony. The findings reveal how genetic traits encoded in the viruses, such as increased virulence, can rapidly emerge in pathogenic bacteria during infection.

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"Some bacteriophages—bacteria-infecting viruses—kill their hosts immediately. Others take up residence long-term. These temperate phages ensure their retention within a bacterial host by providing the bug with one or more genetic benefits, such as antibiotic resistance or increased virulence. But when the host bacterium is in trouble, it’s a different matter: the phage rapidly replicates, kills the host cell, and heads off to infect nearby healthy bacteria. By transferring their beneficial genes to new hosts in this way, the viruses “play a key role in bacterial evolution,” wrote James. (my bold)

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"Hardt and colleagues infected mice with two strains of Salmonella bacteria. One strain (donor) contained a phage that encodes a virulence factor, SopE, which helps the bacteria invade host gut cells. The other (recipient) did not. The team introduced small, equal doses of the two strains into the animals to produce an intestinal infection. After as few as 24 hours, phage transfer of the sopE gene from the donor to the recipient strain was apparent. “It was super efficient,” said Hardt.

"So what prompted the transfer? Inside an animal’s gut, Salmonella “gets a severe beating” from the host innate immune system, said Hardt. “They are in real trouble.”
His team therefore hypothesized that the inflammatory environment might be the phage’s signal to escape. To test this idea, the researchers created non-virulent versions of the two Salmonella strains. These strains were able to colonize the gut for approximately three days before causing inflammation, Hardt explained. During this non-inflammatory period, sopE transfer was dramatically reduced, the team showed.

"Furthermore, vaccination of the mice with inactivated Salmonella also significantly repressed phage transfer upon later Salmonella infection. (Vaccination ensures that subsequent infecting bacteria are neutralized by host antibodies rather than innate inflammation.)

“'The study suggests that vaccination can not only protect against bacterial disease; but also reduce the ability of bacteria in the body to transfer genetic material that might enhance virulence or resistance to treatment,” wrote James.

"This previously unappreciated benefit of vaccination should be considered in future immunology studies, Hardt suggested."

Comment: This study shows how viruses take a major role in horizontal gene transfer. Note the bolded sentence. That viruses can be part of an inventive mechanisms that drove evolution has been discussed in other entries previously presented.