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Calcium Makes Germs Cluster: Ion dilution leads cholera bacteria to disperse

A chain of sugars on the surface of cholera-causing bacteria enables the pathogens to clump together in seawater and yet scatter in fresh water, new data suggest. Microbiologists propose that the dispersal facilitates seasonal outbreaks of cholera in coastal areas.

Vibrio cholerae bacteria naturally inhabit both fresh and salt water. Researchers have linked cholera outbreaks to high waters along the coast of Bangladesh, where sea level rises during the annual monsoon. Influxes of pathogen-bearing seawater, driven by monsoon winds, may alter conditions in coastal estuaries and trigger epidemics.

As many bacteria do, V. cholerae cluster on surfaces, such as the bodies of small aquatic animals. Certain genes, called vps genes, enable V. cholerae to stick together in bacterial communities, or biofilms, in both fresh and salt water.

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