In evolutionary rarity, centipedes took genes from bacteria, fungi to produce venom toxins

February 12, 2021

Centipedes' venom is a complex substance. (Pixabay/631372)

At least 10 of centipedes’ genes that encode toxic compounds in their venom originated in bacteria and fungi, suggesting that the transfer of genes between species may be more common in the evolution of venom than previously known.

Publishing their findings last week in Nature Communications, two venom experts said centipedes and other venomous creatures might stand to benefit from this uncommon evolutionary tactic, known as horizontal gene transfer, by receiving fully developed biological weaponry from other organisms.

Centipedes were also established in the study as the first known animal to have obtained genes for venom production from multiple gene families through horizontal gene transfer, demonstrating how unexpectedly prevalent horizontal gene transfers were in their lineage.

Venom, a cocktail of toxins often delivered in a bite or sting for hunting or defense, has independently sprung from evolution more than 100 times. But prior to the centipede study, only a few cases of horizontal gene transfer had been identified in venom evolution, and it was thought to play a minor role. 

Centipedes have been around for nearly 420 million years and were one of the first venomous creatures, but the history of many of their venom compounds is poorly understood, especially since many of the 3,000 centipede species have not been studied in detail.

Ronald Jenner, one of the study’s two authors and a researcher studying venoms in invertebrates at the Natural History Museum in London, said centipedes were model test subjects for studying the “diversity of the venomous world” because their venom-secreting bites are are not dangerous to humans.

“If you want to understand the diversity of these toxic cocktails and where they came from, how did they evolve these weapons, what kind of components are there and how are they made,” Jenner said, “then it's very easy to study groups that are not dangerous, such as centipedes, and to get these fundamental insights.”

Jenner and Eivind Unheim, from the Norwegian University of Science and Technology and the Universities of Oslo and Queensland, used gene sequences from their earlier centipede research to construct evolutionary family trees of numerous centipede species. They had identified which genes were connected to venom production by testing venom samples — samples acquired with the use of electrical forceps and a repurposed coffee press, Jenner said. 

They found between 10 and 12 genes related to venom production that were horizontally transferred into centipedes, a large number of discoveries given the sparse preexisting literature across all venomous species.  One gene family represented in centipedes is also widely used in genetically modified crops as a toxin against pests.

“We have actually done the horizontal gene transfer for this bacteria by putting it deliberately into plants, and hundreds of millions of years ago centipedes decided, 'Actually, we already did this, we put it in our venom,'” Jenner said.

Even one of the four compounds in the very first centipede's venom from 418 million years ago, previously determined in an ancestral reconstruction by Jenner, Unheim and other scientists, had been taken from another organism. The reconstruction had “big error bars” but represented the first time horizontal gene transfer was involved in the evolutionary origin of a species’ venom, Jenner said.

Some of the toxins were enzymes originally used by bacteria to destroy cells and tissues, and centipedes may have adapted to damage prey, digest food or defend themselves.

More research needs to be done to determine whether horizontal gene transfer is surprisingly common in the evolution of venom, or if the centipede is an evolutionary outlier, according to Jenner. Many other venom compounds in a wide range of species have not yet had their origins identified, so some could be the result of horizontal gene transfer, the venom expert said.

“We just hope now that some other people will look at similarly poorly studied venomous groups to see if this phenomenon is more common, because it's quite possible,” he said.

The article, “Phylogenetic analyses suggest centipede venom arsenals were repeatedly stocked by horizontal gene transfer,” was published Feb. 5 in Nature Communications. The authors of the study were Eivind Undheim, Norwegian University of Science and Technology, University of Oslo and University of Queensland; and Ronald Jenner, Natural History Museum (London).

Correction: A previously published version of this article misstated the name of the Natural History Museum. The error has been corrected.

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