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GEN News Highlights : Jun 3, 2009

Scientists Reveal E. coli’s Survival Technique

Incorporating phage DNA into bacterial chromosomes is key, according to paper in The ISME Journal.

Researchers at Texas A&M University's Artie McFerrin department of chemical engineering have discovered how certain types of bacteria integrate virus DNA into their own genetic makeup to increase their chances of survival. Reporting in The ISME Journal, they also found that the formation of biofilms depends on these virus genes. Additionally, they pinpointed the bacterium gene that controls whether virus DNA is expelled in favor of motility or retained to promote growth.

The team was studying the process by which phages attach to E. coli and inject their genetic material into the bacterial cell to replicate and eventually exit the cell. They found that the bacteria had developed a means of not allowing the phage to replicate and leave the cell.

The investigators observed that the bacteria incorporated the phage's DNA material into its own chromosomes. This new diverse blend of genetic material reportedly helped the bacteria to not only overcome the phage but also flourish at a greater rate than similar bacteria that have not incorporated the phage DNA.

“Our research shows that if these bacteria didn't have this particular set of 25 genes that belonged to the old phage it wouldn't be able to grow as fast,” says Thomas K. Wood, Ph.D., who was involved in this study. “If you removed the phage remnant, the bacteria grows five times slower on some carbon sources.” The scientists thus state that bacteria carry about 10 to 20 percent of genes that aren't their own, which allows them to increase their chances of survival by producing diverse progeny.

This is even more important when the bacteria choose to move to a new environment through a process known as dispersal. Dr. Wood’s group found that through an elaborate regulation method, the bacteria are able to retain the virus DNA or expel it. Retention would help the bacteria grow faster but reduces its motility, which is needed when seeking out new environments.

Further exploring this dynamic, Wood and his research group were able to link this regulation process to the formation of biofilms. Besides finding that biofilm formation relies heavily on virus genes present within the bacteria, Dr. Wood's research also uncovered the mechanism for how this takes place.

A protein within the bacteria called Hha has the ability to control whether virus genes are kept within the bacteria or jettisoned. When Hha is turned on, the bacteria expel the virus genes, opting for motility over the ability to form biofilms. Likewise, when Hha is not expressed, the bacteria move slower but grow biofilms at a much faster rate.

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