A FOOD-POISONING bacterium has a clever strategy to cope when nutrients are
scarce. Ruth Massey and her colleagues at Trinity College, Dublin, found that
Salmonella typhimurium can evolve into a new strain that digests
lactose seventy times more efficiently.
The new strain only evolves in solutions that create an osmotic pressure,
such as those of salts or sugars. 鈥淲ithout salt, the mutants can鈥檛 form, but
once they have, it鈥檚 of no more use to them,鈥� says Massey, who is now at the
University of Oxford.
In osmotic solutions, the bacteria鈥檚 DNA coils up, allowing the
lactose-digesting gene to be expressed to a far greater degree (Current
Biology vol 9, p 1477). 鈥淲hat we鈥檝e found is an environmental factor that
causes an adaptive mutation,鈥� says Massey.
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