Cholera Bacterium: Silent Murderers?

A group of scientists have recently discovered the method to cholera bacterium’s madness: horizontal gene transfer‑‑stabbing and killing other bacteria to absorb their DNA. The disease, which is associated with acute watery diarrhea, is often caused by Vibrio cholera (V. cholerae) infection within the small intestine.

Scientists in the lab run by Melanie Blokesch, PhD, at Ecole Polytechnique Fédérale de Lausanne (EPFL) tested several bacterium strains, globally, most of which had been implicated in the 7th cholera pandemic.

They grew these bacteria on chitin surfaces that simulated their natural habitat on crustaceans, and found the tiny spear was not only part of V. cholerae's natural survival system, but it also contributed to the gene transfer that could potentially cause the bacterium to become more resistant to threats, even to antibiotics.

Blokesch’s team learned that V. cholera utilized a “predatory killing device,” type VI secretion system (T6SS), to survive among competitor bacteria. This spring-loaded spear was found to punch holes into neighboring bacteria thereby triggering the release of their genetic material.

Blokesch commented, “Using this mode of DNA acquisition, a single V. cholera cell can absorb fragments containing more than 40 genes from another bacterium. That’s an enormous amount of new genetic information.”

Researchers touted the significant of this study for the sheer fact that horizontal gene transfer (as opposed to vertical gene transfer) is vastly common among bacteria, eventually attributing to antibiotic resistances. Additionally, experts uncovered, “The chitin-mediated activation of the spear-killing device most likely renders the bacterium more dangerous to patients when they ingest it, as this molecular spear might also kill protective bacteria in the human gut.”

As such, the team of scientists are furthering their research to observe the engagement between the horizontal gene transfer and chitin-induced production of the spear. Blokesch concluded, “By studying this interplay, we can begin to better understand the evolutionary forces that shape human pathogens and maybe also transmission of the disease cholera.”