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Stanford University School of Medicine

Analysis of bacteria spanning 50,000 generations offers new insights on evolution

clocks-1424691_1920Mutations in bacterial genomes are thought to occur at a relatively fixed rate, with a random mix of helpful, harmful and neutral mutations. But a study published recently in Nature found that bacterial genomes accumulate more beneficial mutations then previously thought. In addition, the mutation rates were surprisingly variable.

The findings challenge current thinking on bacterial evolution, co-author Jeffrey Barrick, PhD, an assistant professor of molecular biosciences at the University of Texas at Austin, says in a release:

We are used to thinking about evolutionary time being measured in quiet ticks, each one representing neutral mutations accumulating in genomes, with an occasional chime or gong, representing a beneficial mutation. But, under normal circumstances, the evolutionary clock for bacteria may be more cacophonous than quiet.

Barrick and researchers from a handful of institutions sequenced 264 genomes from 12 populations of E. coli. The populations spanned 50,000 generations, as they had been stored in freezers for about 30 years as part of a project at Michigan State University known as the Long-Term Experimental Evolution, which allows researchers to examine how one original population changes over time.

In this study, researchers found that although evolutionary changes differed between populations, most mutations occurred in genome regions that would benefit the bacteria, strengthening a strain's ability to survive. Some of the populations evolved rapidly at first, then decreased their mutation rate, as they became increasingly adapted to their environments. Here's Barrick:

If this holds true for our own microbiomes, it suggests that microbes are always becoming more specialized for competing in their local environment in subtle ways. This could have implications for personalized medicine, as it suggests that E. coli in my gut will evolve idiosyncratic differences from those in your gut over time, for example.

Previously: Happy Birthday, Charles Darwin: Stanford researchers reflect on evolution, Fast-forwarding evolution to select suitable proteins and From finches to cancer: A Stanford researcher explores the role of evolution in disease
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