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article imageCholera's unusual way of killing for DNA found

By Karen Graham     Jan 4, 2015 in Health
Cholera has been a scourge to humanity since ancient times. The dibilitating intestinal infection causes over 100,000 deaths every year. Scientists have now discovered how the bacterium overwhelms and kills its victims.
Researchers at the École Polytechnique Fédérale de Lausanne (EPFL) have discovered the most unusual way the cholera bacterium have of stealing other bacteria's DNA, including some of their own kinds, thus making the bacterium potentially more lethal. The bacterium Vibrio cholera uses a spear to stab and kill other bacteria. The bacterium then "steals" the DNA from the dead cells.
Melanie Blokesch is an assistant professor of microbiology at the Swiss Federal Institute in Lausanne. She is co-author of a paper that was published in the journal Science on Jan. 2, 2015. According to Blokesch, the bacterium uses a "spring-loaded" mechanism in a process called "horizontal gene transfer," making the bacteria more virulent.
The horizontal gene transfer allows the cholera bacteria to absorb the genetic traits of other bacteria. The study suggests this could explain why some people who build up an immunity to some strains of cholera can still be infected by new strains. The addition of new DNA causes a mutation of the cholera bacteria, letting it continue to spread. "That's what we think -- what we see is part of what makes the most virulent strains so virulent," says Blokesch.
Blokesch explained that the "spring-loaded" mechanism is constantly stabbing out at its surroundings. She said, "This weapon is called the "type VI secretion system" (T6SS) and is known to exist in many types of bacteria." When V. cholera come near other bacteria, the spear punches a hole in them, leaving them to die, releasing their genetic material. This phenomenon can affect virulence and antibiotic resistance, say the researchers.
"Using this mode of DNA acquisition, a single V. cholera cell can absorb fragments containing more than 40 genes from another bacterium," says Melanie Blokesch. "That's an enormous amount of new genetic information." This method is just the opposite of conventional or "vertical" passage of genes from parent to offspring.
There are further studies in the works, especially focusing on the interplay between the creation of the bacterium's spear and horizontal gene transfer, says Blokesch. "By studying this interplay, we can begin to better understand evolutionary forces that shape human pathogens and maybe also transmission of the disease cholera," she says.
More about Cholera, horizontal gene transfer, Vibrio cholerae, predatory technique, Contaminated water
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