Time to revise the high school biology textbooks. Turns out the standard image of a sausage-shaped bacterium crawling along lengthwise is obsolete. New research shows that many of these unicellular organisms can stand upright and walk. The secret is type IV pili—grappling hooklike appendages located on the front and back ends of some species. Previously, researchers thought that pili helped the bacteria pull themselves along a flat surface. But a team of microbiologists took video footage of the bacteria involved in cystic fibrosis infections and found two types of motion. "Crawlers" stayed horizontal, moving more slowly but generally in straighter lines, a more energy-efficient way of getting around. "Walkers," like the one shown above, can use their leg-like pili to detach themselves after cell division to stand up and walk away. The walkers moved faster than the crawlers but meandered—a good strategy for exploring new territory. The researchers report online today in Science that they think this exploratory behavior would be especially useful when the bacteria form biofilms—surface-coating conglomerates responsible for many of the most stubborn and fatal diseases.
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