Horizontal gene transfer in stick insects

Insects have adopted the genetic blueprint for an enzyme from microbes

Hard to recognize is this branchlike Malaysian stick insect (Phobaeticus serratipes). © Christoph Seiler
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Surprising takeover: In the genome of stick horrors, researchers have discovered the blueprint for an enzyme that normally only bacteria possess. Therefore, they suspect that the insect must have taken these genes from its intestinal bacteria and incorporated them into its own genome. Such a horizontal gene transfer was previously considered extremely rare in the animal kingdom - but could have played a greater role in evolution than previously thought.

Many herbivores - from cow to termite - rely on the help of bacteria to digest hard plant material. Because the microbes have enzymes that can decompose the poorly degradable plant material, such as pectinases, which break down the stable sugars in the cell walls of the plants. "In order to accommodate such symbionts, herbivores have generally developed blind bags and similar extensions in the gastrointestinal tract, " explains Sven Bradler of the University of Göttingen.

Bacteria enzyme in the fright genome

Unlike the Stabschrecken, insects, which are known for their subtle camouflage as branches or leaves. Their often extremely stretched and thinner body leaves little room for intestinal symbionts. Nevertheless, these insects seem to be able to digest their leaf food without these microbial helpers without problems. How they manage to do this, Bradler and his colleagues have now investigated with the help of gene analysis in 38 species of stick insects.

The surprising discovery: The stick insects carry in their genome even the building instructions for pectinases - and thus for enzymes that actually occur only in bacteria. "The presence of such endogenous pectinases is a new discovery for the stick insects, " explain the researchers. Instead of harboring the microbes, the stick insects have apparently just taken over the genes that are useful for them.

Horizontal transfer of microbes?

However, such an acquisition can only have been through horizontal gene transfer - the direct transfer of genetic material from one organism to another. Such a gene transfer not by heredity, but by exchange has been known especially among bacteria. In contrast, transmission from a bacterium to an insect is extremely rare - or has just not been discovered often enough. display

According to the scientists, the ancestors of today's stick insects must have acquired the genetic blueprint for pectinases around 60 to 100 million years ago. "This could have been a key event in the evolution of stick insects, because it was the independence of the specific bacteria that allowed the insects, their extraordinary body forms produce, "says Bradler.

"Unpredictable ways of evolution"

The researchers suspect that horizontal gene transfer in the animal kingdom may be much more common than previously thought. For the evolution of life, he might have played a previously underestimated role.

"The horizontal gene transfer from a commensal microbe to its host, as here the case, demonstrates the many, unpredictable, and exciting pathways that evolution can take, " the scientists note. (Scientific Reports, 2016; doi: 10.1038 / srep26388)

(Georg-August-University Gttingen, 25.05.2016 - NPO)