Bacterial Gliding Motility: Visualizing Invisible Machinery Extracellular filaments covering the surface of the marine gliding bacterium Saprospira grandis may be its motility organ

M any flagellated species of bacteria can swim in liquids and glide along surfaces, while motile species without flagella only can glide. Much is known about flagella, whose rotary mechanism is believed to be universal. By contrast, gliding motility is a term used to describe various movements on surfaces by several different mechanisms, none of which is fully understood. Saprospira grandis, meaning a large helical decomposer, is a gliding bacterium that was first isolated from the deep sea by J. Gross in 1911. This gram-negative species, which itself looks like a multicellular flexible filament, is also found along seashores in many places, according to R. A. Lewin of the Scripps Institute of Oceanography at the University of California, San Diego.