The Science of Herding Bacteria

Howard Hughes Medical Institute is reporting that its scientists manipulated group behavior in bacteria. Not so simple, of course. Here’s an expalnation:

Using a bioluminescent marine bacterium known as Vibrio harveyi [shown above is a cluster of Clostridium difficile, an unrelated organism –ed.], which lights up when a threshold number of bacteria are present, Bassler’s team explored the workings of a protein called LuxN. LuxN, which sits in the inner membrane that surrounds the bacterial cell’s contents, is the receptor that detects signaling chemicals known as autoinducers released by nearby bacteria. Quorum-sensing bacteria typically use autoinducers to measure two things, Bassler said: "Am I alone or in a group? Am I with friend or foe?" So, when autoinducers signal that a sufficient number of neighbors are nearby, LuxN tells the cell to turn certain genes on or off.
Bassler and her colleagues wanted to understand how LuxN keeps the bioluminescence genes off until enough autoinducer has been released by a quorum of bacteria. They screened 30,000 genetic LuxN mutants of Vibrio harveyi, searching for those that failed to light up and those that lit up before the bacteria reached a quorum.
The team then screened about 35,000 chemicals in search of those that could inhibit the bacteria’s bioluminescence. They found 15 chemicals that did—some with quite potent effects.
By combining data from these two experiments with quantitative analysis of the different LuxN variants, Bassler and her colleagues obtained clues into how the system is built to kick in only when a signaling threshold is reached. The LuxN receptor is positioned in the membrane in a way that allows it to detect autoinducer only when it arrives from the outside of the cell. Autoinducer that is produced inside the cell – that is, to be released into the environment — cannot trigger that cell’s LuxN receptors. "The receptors are poised to ignore the signal until it builds up," Bassler said. "They wait. If they react instantly (to a signal), it can be catastrophic."

Press release: Scientists Manipulate Group Behavior in Bacteria
Flashback: Say What? Bacterial Conversation-Stoppers
Image credit: Wellcome images: A colour-enhanced image showing a cluster of Clostridium difficile on a surface….