25 Jun Scientists show that in bacteria the rate of beneficial mutations
Question
write a summary of the article’s main points. Provide an answer to the question of how they deal genetically with changes to environment to not become extinct.(minimum 500 words)There is no sexual reproduction so how do bacteria cope with changes and not become extinct?
Scientists show that in bacteria the rate of beneficial mutations — those that increase the capacity of
an organism to survive in a particular environment — is much higher than previously thought. In the
case of Escherichia coli, the bacteria studied, this is as much as 1,000 times higher than previously
believed. The study, just published in Science, also suggests that many more genes mutate during
bacteria adaptation to a new environment than previously thought. Both results – a much higher rate
of advantageous mutations and a bigger number of genes mutating – have important implications for
studies in antibiotic resistance and also how bacteria develop the capacity to attack their host.
Portuguese scientists show that in bacteria the rate of beneficial mutations – those that increase the
capacity of an organism to survive in a particular environment – is much higher than previously
thought.
In the case of Escherichia coli, the bacteria studied, this is as much as 1,000 times higher than
previously believed. The study, just published in Science, also suggests that many more genes
mutate during bacteria adaptation to a new environment than previously thought. Both results – a
much higher rate of advantageous mutations and a bigger number of genes mutating – have
important implications for studies in antibiotic resistance and also how bacteria develop the capacity
to attack their host.
Natural selection – the basis of evolution – is the process by which some organisms are more
capable of life and self-reproduction because they are better fitted to a particular environment. And
mutations are the raw material of evolution, in the sense that they are the source of new
characteristics which equip the adapted organism with a bigger or smaller chance of survival.
But mutations can be either beneficial or disadvantageous, and although beneficial mutations are the
crucial force behind adaptation and survival to a new environment, disadvantageous mutations are
much better studied.
There are several reasons for this, the first relies on the fact that while “bad” mutations are very
easily seen – the organism tends to die and disappear – “good” mutations tend to have a very small
effect in the overall adaptation of individuals and so are easily missed. The fact that beneficial
mutations with big effects are rare is because when an organism is already living in a particular
environment means that is already adapted to it, and so does not need (or can even go through)
radical changes.
The second reason is because in big populations where organism reproduce very quickly and many
beneficial mutations occur at the same time – and these are the only populations where the studies
can be done, since only in them evolution occurs on a visible timescale – there is competition
between organisms with different mutations. This means that in the end, those with the most
beneficial mutations will be reproducing in higher numbers masking the other mutations – this
process is called “clonal interference” – and leads to an underestimation of the mutation rate.
The difference in the study of Lidia Perfeito, Isabel Gordo and colleagues from the Institute
Gulbenkian of Science in Lisbon, Portugal, is that they measured the mutation rate of Escherichia
coli in many different sized populations, including some small enough to avoid clonal interference
although big enough to avoid disadvantageous mutations to spread too easily and kill the population.
Through the comparison of these different size populations, which ranged from to 20,000 cells to 10
million, Perfeito, Gordo and colleagues reached an amazing conclusion: that Escherichia coli
mutation rate was a thousand times bigger than previously predicted and that thousand of mutations
were going overseen because “better” ones overtook them in the population.
Although these studies were done in Escherichia coli – a very common bacterium found in the
intestine of vertebrates, including man – the research by the group of Portuguese scientists
potentially applies to any bacteria and will be especially important in the study of disease-inducing
bacteria.
The importance of Perfeito, Gordo and colleagues’ results resides in two facts: first the fact that they
show that beneficial mutations in bacteria are much more common than previously predicted
suggesting that bacteria can adapt both to anti-bacterial medication, but also to their host, much
quicker than previously thought and second the fact many more bacterial genes are mutating than
those seen in the population what can have implications for the way evolution is understood.
As the team leader explained to the Portuguese Agency of News Lusa, "This study is a substantial
contribution to the understanding of a central problem in the theory of evolution and has important
implications for public health, more specifically for the understanding of antibiotic resistance and the
development of new medicines against bacteria."
Reference: Science – 317, 813 (2007), “Effects adaptive mutations in bacteria: high rate and small”
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