Random Event Triggers Cellular Switch | October 20, 2008 Issue - Vol. 86 Issue 42 | Chemical & Engineering News
Volume 86 Issue 42 | p. 52 | Concentrates
Issue Date: October 20, 2008

Random Event Triggers Cellular Switch

Department: Science & Technology
One E. coli cell (yellow) switches lactose metabolism phenotypes, whereas nearby cells do not.
Credit: © 2008 Science
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One E. coli cell (yellow) switches lactose metabolism phenotypes, whereas nearby cells do not.
Credit: © 2008 Science

A stochastic single-molecule event is enough to switch a bacterial cell from one phenotype to another. By monitoring fluoresce.ntly labeled lactose permease with single-molecule live-cell imaging, Harvard University chemistry professor X. Sunney Xie and coworkers investigated how Escherichia coli cells switch lactose metabolism phenotypes (Science 2008, 322, 442). At intermediate concentrations of the inducer compound methyl-β-D-thiogalactoside (a lactose analog), a population of genetically identical cells stably coexists in two phenotypes. Uninduced cells, which can't metabolize lactose, have a small number of membrane-bound permeases, whereas induced cells, which can metabolize lactose, have many membrane-bound permeases and fluoresce brightly. A cell expresses a large burst of permease only if the transcription factor lac repressor completely dissociates—an infrequent occurrence—from the DNA. The much more frequent partial dissociation of the repressor from the DNA leads to small bursts of permease expression that aren't sufficient to switch the cell's phenotype. "We show that a single-molecule stochastic event solely determines a cell's phenotype," Xie says. "This argues for why single-molecule live-cell studies are important for biology."

 
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