The non-technical word for a biofilm is gunk.

Biofilms — communities of bacteria that band together for protection — gum up pipes, accumulate on ship's hulls and slime the ice machine.

And if you listen to your dentist, you try to brush them off your teeth at night, too.

Because some biofilms cause real problems by blocking the flow of water or oil through pipes and force ships to use more fuel, scientists are interested in understanding how bacteria form in and on them.

What they found surprised them. When most bacteria encounter a hard surface upon which they might form a biofilm, the bacteria stand up. And "walk" across the surface.

"It was totally shocking," said Jacinta Conrad, a chemical and biomolecular engineer at the University of Houston.

Conrad and colleagues describe the phenomenon in a paper published in Friday's issue of the journal Science.

Using advanced microscopes they essentially captured movies of more than 1,000 bacteria as they went from water to encountering a hard surface, and then tracked the individual motions of each bacteria over time.

Bacteria are tiny organisms that live in every habitat on Earth, from the Arctic to extremely hot subsea vents. By cell count, the human body is about 90 percent bacteria.

The bacteria studied in Conrad's experiment were about 1 micron wide and 3 or 4 microns long. A human hair is about 100 microns across.

To find nutrients bacteria must be able to move efficiently.

Scientists have long understood how the microorganisms do this in water. And on surfaces scientists believed the bacteria would lay, lengthwise, and pull themselves along with grappling-hook-like tentacles called pili. And indeed some of the bacteria did this as it was an efficient way of moving in a straight direction.

But that's not a good way of covering a lot of ground, or searching a wide area for food, Conrad said. What is an efficient way, apparently, is the standing up and walking observed by the scientists. This walking on a few pili allowed the bacteria to randomly cover much more space.

The scientists also found differences in how biofilms form depending on the ability of a species of bacteria to walk upright, or not.

This kind of information, ultimately, should help scientists prevent unwanted biofilms from forming.

"I'm really interested in trying to design surfaces that shed bacteria," Conrad said.

The type of surfaces, one supposes, that bacteria would turn around and walk away from.

eric.berger@chron.com