Kon-Tiki, Bacteria Style

7 May 2010 5:10 pm

Maille Lyons

Marine snow. Waterborne bacteria can live long and prosper on chunks of detritus like this one.

Dangerous bacteria may be rafting their way to a beach near you. New research reveals that, just like a rat clinging to a piece of floating wood after a flood, pathogenic microorganisms can set up shop aboard drifting bits of fish feces and other debris and ride them to far-flung destinations. Understanding more about the process should help public health officials develop better strategies to fight waterborne diseases and seafood contamination.

Marine biologist Maille Lyons of Old Dominion University in Norfolk, Virginia, has been studying waterborne bacteria for nearly a decade. She and her colleagues already knew that beneficial microorganisms could be carried about by currents as they established colonies on floating pieces of organic matter known as marine snow. The bacteria live off bits of the snow and convert it into the raw organic material necessary for the health of the marine food web, from plankton to killer whales. "Bacteria are among the aquatic world's recyclers," says Lyons.

But in the new study, Lyons and colleagues uncovered a chilling twist. It turns out potentially virulent pathogens such as Escherichia coli likewise latch onto marine snow. The researchers collected water from a storm drainage pipe emptying into southeastern Virginia's Lafayette River, a tributary of the Chesapeake Bay. Then they placed the water in tanks that swirled it to simulate currents and compared bacterial colonies living on marine snow with those living in snow-free water. Reporting online this week in Aquatic Microbial Ecology, the team found that the snow-dwelling bacteria survived for the entire 35 days of the study, but those in detritus-free water samples died off, presumably from starvation, in as little as 2 days.

The longer life span for the snow-dwelling bacteria means that they can travel much farther from pollution sources than previously thought. That means, Lyons says, that researchers need to develop new models about how waterborne diseases are spread by pathogens living on marine snow. "The more we understand about their basic biology and ecology, the better we will be at predicting their abundance, persistence, dispersal, and outbreaks," she says.

Microbiologist Rebecca Gast of Woods Hole Oceanographic Institution in Massachusetts points to an additional risk. Along with helping dangerous microbes to survive longer in the water, she explains, the marine-snow colonies may help to increase their concentration, "resulting in exposure to higher levels than would normally be encountered if the [pathogens] were floating free."

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