The National Science Foundation (NSF, www.nsf.gov) reported this week that scientists studying how marine bacteria move have discovered that a sharp variation in water current segregates right-handed bacteria from their left-handed brethren, impelling the microbes in opposite directions. According to the NSF, this finding and the possibility of quickly and cheaply implementing the segregation of two-handed objects in the laboratory could have a big impact in the pharmaceutical industry, for which the separation of right-handed from left-handed molecules can be crucial to drug safety.

While single-celled bacteria do not have hands, their helical-shaped flagella spiral either clockwise or counter-clockwise, making opposite-turning flagella similar to human hands in that they create mirror images of one another. This two-handed quality is called chirality, and in a molecule, it can make the difference between healing and harming the human body.

One of the best-known instances of a chiral molecule causing widespread harm occurred in the 1950s, when the drug thalidomide was given to pregnant women to prevent morning sickness.

One naturally occurring form, or isomer, of thalidomide reduces nausea; the other causes birth defects. In another commonly used chiral drug, naproxen, one isomer is analgesic; the other causes liver damage.

In a paper published in the journal Physical Review Letters (prl.aps.org), the researchers describe how they designed a microfluidic environment — a device about the size of an iPod nano that has channels containing water and bacteria — to create a “shear” flow of layers of water moving at different speeds.

In their tests, the researchers used a non-motile mutant of the bacterium Leptospira biflexa, whose entire body has the shape of a right-handed helix. They injected the Leptospira into the center of the microfluidic device and demonstrated that the bacteria drift off-course in a direction dictated by their chirality.

The researchers also developed a mathematical model of the process, and are implementing this new approach to separate objects at molecular scales.

To read the NSF’s full report on this story, click here.