Team finds a better way to watch bac...( CHAMPAIGN Ill. Researchers have dev...)

CHAMPAIGN, Ill. Researchers have developed a new method for studying bacterial swimming, one that allows them to trap Escherichia coli bacteria and modify the microbes' environment without hindering the way they move.

The new approach, described this month in Nature Methods, uses optical traps, microfluidic chambers and fluorescence to get an improved picture of how E. coli get around.

The microfluidic chambers provide a controlled environment in which the bacteria swim, and allow the researchers to introduce specific stimuli such as chemical attractants to see if the microbes change direction in response to that stimulus.

Optical traps use lasers to confine individual cells without impeding their rotation or the movement of their flagella. University of Illinois physics professor Yann Chemla, who co-led the study with physics professor Ido Golding, calls the optical traps "bacterial treadmills."

Movement of the bacterial cell alters the light from the laser, allowing the researchers to track its behavior.

Fluorescent markers enhance visualization of the bacteria and their flagella under a microscope.

Three to six helical flagella emerge from various points along E. coli's rod-shaped body. When they rotate in a counterclockwise fashion (as seen from behind), they gather into what looks like a coordinated bundle that pushes the bacterium forward, causing it to corkscrew through its environment. But when one or more flagella rotate in the opposite direction, they splay apart, reorienting the bacterium.

This "run and tumble" behavior has long been of interest to scientists for two reasons, Golding said. First, the elaborate mechanics of bacterial swimming "tell you a lot about biomechanics," he said. And second, "it serves as a paradigm for the way living cells process information from their environment."

Earlier studies have been unable to follow individual bacterial cells movi
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