October 16, 2021

Microbes can defy the laws of evolution

A new discovery has found that some pathogens successfully violate the laws of evolution. In most living organisms, evolution and adaptation are driven by vertical gene transfer, in which genetic material is passed from parents to their offspring. Now, however, scientists have come across an alternative form of DNA transfer in which genetic material is passed horizontally between bacteria. In this way, the laws of evolution are circumvented, and various positive characteristics arise among populations that have not been exposed to the evolutionary pressures that led to the emergence of the particular specific adaptation in the first place.

The study, published in the scientific journal PNAS, sheds more light on the spread of antibiotic-resistant bacteria.

Genes that allow bacteria to survive exposure to antibiotics are most commonly found in hospitals, sewers and farms. However, they can also be found in more unusual places – such as forests and estuaries. Although bacteria are not exposed to antibiotics here, as in hospitals, sewers and farms, they still manage to acquire these resistant genes. This is one of the reasons why antibiotic resistance has literally doubled in the last 20 years.

Scientists wanted to understand how these resistant genes spread in the environment. To this end, they study antibiotic-sensitive bacteria in the laboratory – they grow them in an intermediary that does not contain antibiotics, but does not inhibit the process of horizontal gene transfer from antibiotic-resistant bacteria. Using a complete genomic sequence, the researchers were able to confirm that genes from the antibiotic-resistant bacterium are spreading in populations – even without selection. Subsequently, these new populations, resulting from horizontal gene transfer, managed to survive exposure to high concentrations of antibiotics.

The discovery shows why antibiotic resistance has evolved so rapidly in hospitals and how antibiotic resistance genes appear in populations that have never been exposed to antibiotics before.

“Bacteria (and their DNA) are constantly transported over long distances by wind, water, animals and humans,” study author Dr. Mike MacDonald told IFLScience. “When bacteria (or their DNA) move, conditions for horizontal gene transfer are created.”

It was previously thought that this adaptation could only be transmitted between populations that were exposed to selection pressure, but this study shows that (at least in terms of antibiotic resistance) genes can spread among populations without any obvious benefit.

“What we found during our laboratory experiments is that antibiotic genes can also occur in conditions without antibiotics, without being of significant benefit to the bacteria themselves. It is enough to have a horizontal transfer of genes “and the price is not too high, says MacDonald.

“This study shows us that the use of antibiotics in one place – for example on a farm – can lead to antibiotic resistance in another place, where genes can lead to new, dangerous combinations.”

Source: IFLScience