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An environmentally dependent method to excise particular genes and eliminate genetically modified organisms (GMOs) if they leave the lab, published this week (May 19) in Nature Communications, uses an inducible CRISPR/Cas9 genome-editing system to snip out vital pieces of the E. coli genome.

Sonnenburg, his wife Erica, and the graduate student Samuel Smits confirmed this idea in a recent experiment. The researchers started with mice that had been raised in sterile bubbles and then loaded with identical collections of gut microbes. They then fed these mice a high-fiber diet, before randomly switching half of them to low-fiber chow for seven weeks. Predictably, the fall in fiber caused upheavals in the rodents' guts. In the low-fiber group, the numbers of 60 percent of the local microbe species fell dramatically, and some remained low even after the mice returned to high-fiber meals. Those seven low-fiber weeks left lingering scars on the animals' microbiomes.