Animal Defenses Stolen from Bacteria

Animal Defenses Stolen from Bacteria

In a surprising finding, microbiologists at the University of Washington and the Fred Hutchinson Cancer Search Center find evidence of at least six horizontal gene transfer events from bacteria to eukaryotes. While horizontal transfers are common between bacteria, this research, published in Nature, is one of the few to note transfers to eukaryotes. Specifically, their analyses show that type VI secretion amidase effector (a bacteriocidal enzyme) was transferred to several arthropods and acquired eukaryotic secretion signals. In the deer ticks, the gene provides a distinct adaptive advantage by limiting proliferation of Borrelia burgdoferi (Lyme disease).

Specifically, their ability to inject deadly toxins into rival cells was appealing.

"When we started digging into genome databases, we were surprised to find that toxin genes we thought were present only in bacteria were also in several animals," co-author Matt Daugherty, from Fred Hutchinson Cancer Research Center in Seattle, said in a statement. "We immediately started wondering why they were there."

Among the many animals that adopted this bacterial artillery were ticks and mites. The results showed that the toxic genes found in bacteria had become permanently incorporated into the genomes of these animals, via a process known as horizontal gene transfer.

Such transfer events are common between microbes, but very few instances have been recorded of it occurring between bacteria and more complex organisms.

Ticks, for instance, carry pathogens in their guts and transmit them through their saliva when they feed on animals, delivering them a toxic bite.

Researchers were particularly interested in this mechanism in deer ticks, which are known for their ability to transmit Lyme disease.

"We were excited to see this in the deer tick, given the increasing prevalence of Lyme disease in North America. Lyme disease is caused by a bacterium, so we speculated that the transferred antibacterial toxin might affect how the tick interacts with the Lyme disease agent," explained co-author Seemay Chou.

Researchers plan to investigate how the toxins function in organisms other than ticks, and what other types of bacterial toxins may have been repurposed by animals as a means of defense.

The findings were published in the journal Nature.