Fluorescent Bacteria Keep Time Like a Clock

One small step for flashing bacteria, one giant leap for synthetic biology. In a new Nature study, molecular biologist Jeff Hasty and his team say they have created a line of E. coli bacteria that flash in fluorescent light and keep time like a clock.

Previously, scientists had engineered only single cells to become oscillators — devices that could count time by performing a particular activity on a cyclical schedule [Nature News]. Back in 2008, Hasty and his team created an oscillator for single cells that could be set to temperature or chemical triggers. But now the researchers have induced a whole host of bacteria to work together to keep time by taking advantage of the way they collaborate naturally: quorom sensing.

Quorum sensing enables bacteria to change their behaviour once they reach a critical density. For example, at high densities, the bacterium Vibrio fischeri, which lives on the skin of squid, starts to light up, helping to camouflage the squid, but V. fischeri living in isolation don’t glow, saving their energy for swimming instead [New Scientist]. Hasty’s engineered bacteria express three new proteins: a sort of catalyst molecule called AHL, a fluorescent protein, and a chemical “off switch.” When just a few engineered E coli clump together, they produce AHL but nothing else happens. When enough bacteria congregate, the AHL causes the cells to produce the the next two proteins, and the fluorescent protein causes them to be suffused with a bright glow. However, when the concentrations of the chemical “off switch” get high enough the whole system shuts down, which it why it oscillates like a clock.

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