Study shows small animals use genes ‘stolen’ from bacteria to protect themselves against infections

Some small freshwater animals are protecting themselves from infections by using antibiotic recipes “stolen” from bacteria, according to new research led by a team from the University of Oxford, the University of Stirling and the Marine Biological Laboratory (MBL) at Woods Hole.

These tiny creatures are called bdelloid rotifers, which means “wheel-shaped crawling animals.” They have a head, mouth, gut, muscles, and nerves like other animals, although they are smaller than the thickness of a hair.

The study found that when these rotifers are exposed to a fungal infection, they activate hundreds of genes that they have acquired from bacteria and other microbes. Some of these genes produce resistance weapons, such as antibiotics and other antimicrobial agents, in the rotifers. The team reports their findings in Nature Communications.

“When we translated the DNA code to see what the stolen genes did, we had a surprise,” said Chris Wilson, lead author of the study at the University of Oxford. “The key genes were instructions for chemicals we didn’t think animals could make. They looked like recipes for antibiotics.”

Previous research has shown that rotifers have been picking up DNA from their environment for millions of years, but the new study is the first to find that they use these genes to fight disease. No other animal is known to “steal” genes from microbes on such a scale.

“These complex genes, some of which are not found in any other animal, were acquired from bacteria but evolved in rotifers,” said study co-author David Mark Welch, senior scientist and director of the Josephine Bay Paul Center at the Marine Biological Laboratory. “This raises the possibility that rotifers could produce new antimicrobials that might be less toxic to animals, including humans, than those we develop from bacteria and fungi.”

Recipes for self-defense

Antibiotics are essential to modern health care, but most of them weren’t invented by scientists. They’re produced naturally by wild fungi and bacteria, and humans can make artificial versions of them to use as medicines.

The new study suggests that rotifers might do something similar.

“These strange little animals have copied the DNA that tells microbes how to make antibiotics,” Wilson says. “We watched them use one of these genes against a disease caused by a fungus, and the animals that survived the infection produced ten times more of this chemical formula than those that died, indicating that it helps suppress the disease.”

Scientists believe rotifers could provide important clues in the search for drugs to treat human infections caused by bacteria or fungi.

Antibiotics are becoming less effective because disease-causing microbes have become resistant and no longer respond to treatment. The World Health Organization recently sounded the alarm, warning in a report published in June of the “urgent need” to develop new antibiotics to counter the threat of resistance.

“The recipes used by rotifers appear to be different from the known genes of microbes,” said study author Reuben Nowell of the University of Stirling. “They are just as long and complicated, but some parts of the DNA code have changed. We think the recipe has been modified by an evolutionary process to produce new and different chemicals in rotifers. This is exciting because it could suggest ideas for future medicines.”

The genes that rotifers acquired from bacteria encode an unusual class of enzymes that assemble amino acids into small molecules called nonribosomal peptides.

“The next phase of this research should involve the identification of multiple non-ribosomally synthesized peptides produced by bdelloid rotifers, and establishing the conditions under which the synthesis of these compounds can be induced,” said study co-author Irina Arkhipova, senior scientist at the Marine Biological Laboratory.

One problem with developing new drugs is that many antibiotics produced by bacteria and fungi are toxic or cause side effects in animals. Only a few of these can be turned into treatments that eliminate harmful microbes from the human body.

If rotifers already produce similar chemicals in their own cells, they could pave the way for safer drugs for use in other animals, including humans.

Why do rotifers acquire so many foreign genes?

The big question is why rotifers are the only animals that borrow these useful genes from microbes at such high rates.

“We think this might be related to another strange fact about these rotifers,” said study co-author Tim Barraclough of the University of Oxford. “Unlike other animals, we never see male rotifers. Rotifer mothers lay eggs that hatch into genetic copies of themselves, without the need for intercourse or fertilization.”

According to one theory, animals that copy each other in this way can become so similar that they begin to become unhealthy.

“If one of them gets a disease, the others will too,” Barraclough says. Because bdelloid rotifers don’t have sex, allowing parental genes to recombine in a beneficial way, the mother rotifer’s genome is transferred directly to her offspring without introducing new variation.

“If rotifers don’t find a way to modify their genes, they could go extinct. That could explain why these rotifers have borrowed so many genes from other regions, especially anything that helps them deal with infections,” Barraclough said.

Nowell believes there is still much to learn about rotifers and their stolen DNA.

“Rotifers used hundreds of genes that don’t exist in other animals. The antibiotic recipes are exciting, and some other genes even appear to have been taken from plants. These discoveries are part of a growing story about how genes are moved between different types of life,” he said.