Genetic exchange free and easy at sea

by Kiri Beilby

In the study, a group of Rhdobacter capsulatus were genetically marked with an antibiotic resistant gene. These modified strains were put with natural communities, and the resultant antibiotic resistance was then measured.

Credit: Lauren McDaniel

SYDNEY: Chromosome swapping between marine bacteria is up to millions of times more frequent than thought and may blur the species lines.

The process is known as horizontal gene transfer (HGT), as oppose to the ‘vertical’ swapping between generations from parent to offspring. The microbes pack up random bits of chromosomes that are then transferred between individuals via a virus-like infection.

Marine biologists observed the rate at which this occurs in the order Rhodobacterales, and it was 650 000 to 31 million times greater than what was previously measured, they reported in the journal Science.

Watching evolution in action

“For me, the most exciting part about this project is that we are watching evolution in action,” said Lauren McDaniel, from The University of South Florida in Saint Petersburg.

Oceanic bacteria perform a range of important environmental functions that include greenhouse gas metabolism and the cycling of natural elements and molecules around the globe. Their amazing ability to perform diverse functions, teamed with an extraordinary resilience when faced with environmental threat, suggests a high incidence of adaptation is taking place.

“I have observed that scientists like to categorise things like bacteria and put them in neat little bins like ‘species A’ or ‘species B’ in order to potentially predict their behavior. While this may work for higher organisms, bacteria may actually exist more as a continuum than discrete species,” said McDaniel.

Gene transfer

In the study, a group of Rhdobacter capsulatus were genetically marked with an antibiotic resistant gene. These modified strains were put with natural communities, and the resultant antibiotic resistance was then measured.

The researchers were surprised to find such a rapid transfer of genetic information, which was 47% higher through direct transfer than through self-moderated changes.

Once the DNA is exchanged between individual bacteria it mingles with the host version and incorporates itself - similar to the process that takes place in sexually reproducing animals when integrating DNA from both the mother and the father.

Seeing bugs on a whole new level

“The widespread trait of horizontal gene transfer among bacterial communities may in fact be massively higher than currently estimated, and this may allow bacteria to take on new traits to enhance their fitness and capacity to deal with challenges,” said Staffan Kjelleberg, an environmental microbiologist at the University of New South Wales.

This finding adds to our appreciation of microbial adaptive capacities, illustrating a response by entire communities of bacteria not just individuals that are selected for or against during environmental change or need, he said.

“How bugs adapt is so beautiful! And in this study we see it on a whole new level,” adds Kjelleberg.

http://www.cosmosmagazine.com/news/3808/horizontal-gene-transfer-sea