Nav: Home

Evolutionary 'selection of the fittest' measured for the first time

March 10, 2016

A difference of one hundredth of a percent in fitness is sufficient to select between winners and losers in evolution. For the first time researchers have quantified the tiny selective forces that shape bacterial genomes. The story is published today in the prestigious journal PLoS Genetics.

Darwin's Theory of Evolution introduced the concept of 'survival of the fittest'. At each generation the 'fittest' individuals are selected and this is a major force shaping the biological world we see today. Selection can explain why a cheetah runs fast - cheetah's that run fast catch the food to feed their cubs. Those that don't run fast get less food, and fewer cubs survive. Over time evolution selects against cheetahs that cannot run fast enough. But, how fast is fast enough, and big does the difference have to be before selection is effective? This question was asked by two researchers at Uppsala University, graduate student Gerrit Brandis and Professor Diarmaid Hughes.

Brandis and Hughes used Salmonella (a bacterium that causes infections in humans and animals) to measure the power of selection to choose the fittest individuals. Salmonella is similar to animals like cheetahs in the sense that it competes for food and is under intense selection to use that food to grow as fast or faster than any other individuals in the same environment. Evolution selects for the fittest variants.

To grow, bacteria, like all living organisms, must translate their genetic code into amino acids that are joined together to make proteins. The speed of translation determines how fast Salmonella can grow. Translation is one of the most ancient processes in biology and has been under selection for billions of years on earth.

The genetic code has 'redundancy', meaning that there are several different 'codons' that can be translated into any one amino acid. For some amino acids up to 6 different codons can be used. Brandis and Hughes asked whether it mattered which particular codons were used to make EF-Tu, one of the most important proteins in Salmonella.

Brandis and Hughes changed many different codons and showed that changing even a single codon in the gene for this protein into any one of the alternative 'synonymous' codons reduced the 'fitness' of Salmonella. The codons that are actually used by Salmonella are the very best, and any change reduces the fitness of the bacteria.

Brandis and Hughes quantified the fitness cost of changing codons in this gene. On average, changing a single codon reduced the fitness of the bacteria, by 0.01 procent per generation. This tiny change in fitness is big enough for evolution to select the 'fittest' DNA sequence and causes what is called 'codon usage bias' - the widespread use of particular codons to make highly expressed proteins. Codon usage bias is found in nearly all fast-growing organisms, including bacteria and yeasts that cause infections in humans. Evolution has shaped their translation machinery so that they can grow as rapidly and efficiently as possible - not necessarily good for us, but good for the survival of bacteria and yeast.

- The message is that evolution, working over very long time scales (hundreds of millions of years), can select tiny differences in relative fitness, as small or smaller than 0.01procent per generation for Salmonella, says Diarmaid Hughes.
-end-


Uppsala University

Related Bacteria Articles:

Conducting shell for bacteria
Under anaerobic conditions, certain bacteria can produce electricity. This behavior can be exploited in microbial fuel cells, with a special focus on wastewater treatment schemes.
Controlling bacteria's necessary evil
Until now, scientists have only had a murky understanding of how these relationships arise.
Bacteria take a deadly risk to survive
Bacteria need mutations -- changes in their DNA code -- to survive under difficult circumstances.
How bacteria hunt other bacteria
A bacterial species that hunts other bacteria has attracted interest as a potential antibiotic, but exactly how this predator tracks down its prey has not been clear.
Chlamydia: How bacteria take over control
To survive in human cells, chlamydiae have a lot of tricks in store.
Stress may protect -- at least in bacteria
Antibiotics harm bacteria and stress them. Trimethoprim, an antibiotic, inhibits the growth of the bacterium Escherichia coli and induces a stress response.
'Pulling' bacteria out of blood
Magnets instead of antibiotics could provide a possible new treatment method for blood infection.
New findings detail how beneficial bacteria in the nose suppress pathogenic bacteria
Staphylococcus aureus is a common colonizer of the human body.
Understanding your bacteria
New insight into bacterial cell division could lead to advancements in the fight against harmful bacteria.
Bacteria are individualists
Cells respond differently to lack of nutrients.

Related Bacteria Reading:

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Moving Forward
When the life you've built slips out of your grasp, you're often told it's best to move on. But is that true? Instead of forgetting the past, TED speakers describe how we can move forward with it. Guests include writers Nora McInerny and Suleika Jaouad, and human rights advocate Lindy Lou Isonhood.
Now Playing: Science for the People

#527 Honey I CRISPR'd the Kids
This week we're coming to you from Awesome Con in Washington, D.C. There, host Bethany Brookshire led a panel of three amazing guests to talk about the promise and perils of CRISPR, and what happens now that CRISPR babies have (maybe?) been born. Featuring science writer Tina Saey, molecular biologist Anne Simon, and bioethicist Alan Regenberg. A Nobel Prize winner argues banning CRISPR babies won’t work Geneticists push for a 5-year global ban on gene-edited babies A CRISPR spin-off causes unintended typos in DNA News of the first gene-edited babies ignited a firestorm The researcher who created CRISPR twins defends...