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How bacteria turbocharged their motors


The discovery, by a team from Imperial College London, provides insights into evolution at the molecular scale.

Bacteria use molecular motors just tens of nanometres wide to spin a tail (or 'flagellum') that pushes them through their habitat. Like human-made motors, the structure of these nanoscale machines determines their power and the bacteria's swimming ability.

Previously, the team from the Department of Life Sciences at Imperial looked at these motors and discovered a key factor that determined how strongly bacteria could swim. Like human-made motors, bacterial motors have distinct 'stator' and 'rotor' components that spin against each other. 

The team found that the more stator structures the bacterial motor possessed, the larger its turning force, and the stronger the bacterium swam. Despite these differences, DNA sequence analysis shows that the core motors are ancestrally related. This led scientists to question how structure and swimming diversity evolved from the same core design.

Now, in new research published today in the journal Scientific Reports, the researchers were able to build a 'family tree' of bacterial motors by combining 3-D imaging with DNA analysis. This allowed them to understand what ancestral motors may have looked like, and how they could have evolved into the sophisticated motors seen today.

The team found a clear difference between the motors of primitive and sophisticated bacterial species. While many primitive species had around 12 stators, more sophisticated species had around 17 stators. This, together with DNA analysis, suggested that ancient motors may also have only had 12 stators. 

This clear separation between primitive and sophisticated species represents a "quantum leap" in evolution, according to the researchers. Their study reveals that the increase in motor power capacity is likely the result of existing structures fusing. This forms a structural scaffold to incorporate more stators, which combine to drive rotation with higher force.

Lead researcher Dr. Morgan Beeby said: "We are used to observing evolution at the scale of animals or plants, such as the giraffe's neck slowly getting longer over time to reach previously inaccessible food.

"However, the evolution at the molecular scale is much more radical.. It's like a giraffe having children with necks suddenly a metre longer."


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