Bacteria are picky eaters and swim for a better meal

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Dr Jean-Baptiste Raina

For about 40 years, scientists have known that bacteria are able to swim. But it took eight years of research for Dr. Jean-Baptiste Raina discover that this is a skill they actively use in the ocean, and they use it to find their favorite food.

Raina, a microbial ecologist at the University of Technology Sydney, and her team published their discovery today in the journal Nature.

“There are about five million bacterial cells in every teaspoon of seawater – an enormous density of cells.” says Raina.

“The fact that bacteria swim and can respond to their favorite food is a big issue because of the sheer number of bacteria in the ocean,” he says.

How do you track bacteria swimming in the ocean?

To make their discovery, Raina and her team had to devise a way to observe bacteria in the open ocean. To do this, they created a piece of plastic the size of a credit card with tiny pits – an invention dubbed the ISCA (In Situ Chemotaxis Assay). Despite its apparent simplicity, the ISCA is an elegant and sophisticated scientific device.

Each well is filled with a different food source before the card is placed in the ocean. Food sources are made up of different species of photosynthetic algae that are tasted by bacteria. The chemical signatures of these algae then spread through the water.

Just as sharks sniff and swim towards blood, bacteria detect these chemical signatures and come swimming. Once attracted to the well, the bacteria are captured using a technology called microfluidics. Raina can then retrieve the plastic card and see which bacteria went to which food source.

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Credit: Dr Jean-Baptiste Raina

Using fussy bacteria to get better climate models

While many of us associate bacteria with scary pathogens, Rainer emphasizes that most ocean bacteria are harmless. But they influence the ocean’s carbon cycle, the nitrogen cycle, and the production of gases that impact the atmosphere.

“Their role really sustains aquatic environments,” says Rainer.

Raina says her work will help inform the way ocean processes are modelled, including creating climate models.

Bacteria have been considered in these models for decades, but being able to get a better sense of their behavior will make the modeling more robust.

“Adding that specific information can really tweak these models,” he says.

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