Partners in Battle: How ancient bacteria help beetles build suits of armor

Researchers showed that beetles supply both the missing ingredients and muscle power to complete the pathway leading from the Nardonella’s production of tyrosine to the beetle’s acquisition of a nearly impenetrable exoskeleton. (Siga/Wikimedia Creative Commons)

More than 100 million years ago, an ancient bacterium named Nardonella began forming a bond with a beetle. Today, beetles have such an intimate relationship with Nardonella that both the bacterium’s and beetle’s genetics – the blueprints that define them – have irreversibly changed in response to each other.

Their common goal: build an armor-like exoskeleton fit to withstand nature’s unforgiving battlefield.

A study published last month in the Proceedings of the National Academy of Sciences by Japanese researchers, Hisashi Anbutsu and colleagues, showed unequivocally that the most diverse group of beetles on Earth – the weevils – harbor Nardonella in a special organ reserved for the bacterium that is attached to their intestines.

Inside that organ, Nardonella produces tyrosine, the key ingredient beetles need in order to build exoskeletal armor.

In fact, Nardonella does nothing except manufacture tyrosine. Its genome – the collection of all its genetic information – has been so reduced that Nardonella has lost much of the genetic code that gives other bacteria the ability to live freely outside of a host.

Even though Nardonella can produce tyrosine, the bacterium can’t actually build anything with it. That’s when the beetle comes into play.

Researchers showed that beetles supply both the missing ingredients and muscle power to complete the pathway leading from the Nardonella’s production of tyrosine to the beetle’s acquisition of a nearly impenetrable exoskeleton.

When these researchers genetically knocked away the beetle’s ability to complete that pathway, they got beetles that were reddish, like raw skin, and soft to the touch. They got the same result when they genetically suppressed Nardonella.

By demonstrating these effects, researchers were able to complete the intimate circle connecting Nardonella and its host beetle – a circle that began to evolve over 100 million years ago when the first bees, snakes and pterodactyls came into existence.

The story that continues to unfold between beetles and Nardonella is also unfolding in many other animals, especially insects. Other bacteria often form such close relationships with their hosts that they too begin to shed genes as they become optimized for a particular function.

The most famous of these stories is continuing to unfold within every cell that makes us human. Before there were animals, plants or fungi, Earth was dominated by bacteria for nearly half of its existence. All other creatures began to evolve after one bacterium was swallowed by another and then permanently incorporated.

The bacterium that was swallowed eventually turned into mitochondria, which supplies each of our cells with the energy they need to function. Mitochondria, like Nardonella and other bacteria that live intimately within hosts, have very reduced genomes with just the right assortment of genes needed to get the job done.

Researchers are just beginning to uncover the mysteries of symbiosis – when organisms live together and provide each other with mutual benefits.

For the beetle, it’s clear – armor provides defense against enemies and the environment. For the bacterium, the beetle provides an entire organ as a home – an organ protected from an invisible battlefield where bacteria wage war against each other while fending off hordes of viruses.


Diler Haji is a campus correspondent for The Daily Campus. He can be reached via email at diler.haji@uconn.edu.