Bacteria chat: disrupting bacterial communication systems to flush out cholera

By Kat McGregor

When engaging in battle, a key tactic is disrupting enemy communication. Tufts University in Massachusetts is investigating the phenomena of bacteria communicating with one another, acting as one enormous multicellular organism. This phenomenon is called quorum sensing, bacteria communicating with each other using chemical signals (autoinducers) that they produce and respond to, determining their location and behaviour.

Researchers are investigating what happens when they interrupt bacteria when they are having a chat. The main topic of conversation is gene expression regulation. In the case of Vibrio cholerae, (the bacteria that causes cholera) it switches on their toxin-producing gene when there only a few bacterial cells present, with the potential of killing those of us unlucky enough to be a host.

The World Health Organisation’s latest warning is that up to 4million cases of cholera are happening around the world, every year. Cholera is a highly infectious, bacterial disease. The bacteria produce a toxin that leads to dramatic gastro-intestinal water loss, causing dehydration, and killing more than 143,000 people every year. Oral vaccines do exist, but they are kept out of circulation by inflated prices.

Four quorum sensing receptors have been discovered so far, and Tufts University has begun to investigate the process of flooding these receptors to disrupt the bacterial communication system. Agonists (compounds that activate the receptors) are added to communities of bacteria to “trick” the bacteria into behaving as if it were in a high cell population – and thereby switching off its toxin-producing genes and evacuating the host. Their study involved V. cholerae cells with only one receptor (CqsR) and used one agonist (ethanolamine), and the research has been an overwhelming success; even in tiny cell populations all disease-causing genes remained switched off. This, if developed into a treatment, could save hundreds of thousands of lives a year.

Quorum sensing was first discovered more than 40 years ago when scientists at the University of Harvard investigating an underwater bacterium called Vibrio fischeri, noticed that in an environment with a low density of bacteria, no light was emitted. In contrast, in environments with high cell populations, the cells all began to glow, like being stood in Piccadilly Circus. Many marine animals, such as the Euprymna scolopes squid (pictured below) take advantage of the remarkable properties of these bacterial cells. In return for a warm home and food, the bacteria shine to remove the squid’s shadows, hiding them from predators in the moonlit shallows.

A Euprymna scolopes squid glows. Photograph by Mattias Ormestad, from nationalgeographic.org

Quorum sensing is an incredible phenomenon, explaining the glow of the deep ocean and the ability of tiny organisms to spread throughout large hosts. There is still much to explore and investigate but disrupting communication between these cells has promising implications in fighting infections and controlling global diseases, such as cholera, that are endemic in the developing world.

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Bacteria chat: disrupting bacterial communication systems to flush out cholera