Beware the Toxic and Explosive Blue Backpack This Termite Carries

The video shows a termite worker under attack. Three enemies of another species scramble over its body, limbs dancing and mandibles closing. Suddenly, the attacked worker’s back erupts and caustic foam pours from its body. It will die, but this fountain of toxic material may save its nestmates from the invaders.

Look closer at the video, and you may notice two half-moons of deep blue embedded on this worker’s back. Some years ago, scientists observing this species of termite, Neocapritermes taracua, in French Guiana realized that these blurry shapes were in fact solid knobs of a potent enzyme, tucked into pockets in its carapace. When the termite worker is confronted by dangerous foes, it will rupture a compartment and bring a hitherto mostly harmless fluid into contact with the enzyme, creating that lethal, explosive and nest-defending reaction.

Scientists wanted to get a better look at this perilous enzyme. In a paper published Thursday in the journal Structure, a team of biologists described a detailed analysis they made of the dangerous blue backpack the termites carry, including an unusual bond they identified that may be linked to its deadly burst.

This termite is not the only insect that kills invaders by sacrificing itself, said Jana Škerlová, a structural biologist at the Czech Academy of Sciences and an author of the new paper. For instance, flying ants, which, like termites, are colonial insects, have also been observed performing a similar behavior. When workers in a colony are sterile, they can help their own genes survive by protecting their relatives who can reproduce.

What’s special about Neocapritermes taracua is that, until it is attacked, the insect keeps a relatively innocuous molecule physically separate from an enzyme, named blue laccase BP76. When blue laccase BP76 mixes with that molecule, a single hydrogen atom is removed, turning it into a toxin.

From the enzyme’s color, the researchers suspected it would contain copper atoms, which create a blue hue. They also had hunches about other aspects of its structure, because laccases are common enzymes and have been observed catalyzing reactions involving oxidation in fungi, plants and insects.

But when they obtained a snapshot of the blue laccase’s shape, by beaming X-rays through it, they were surprised to see that it had a strong bond linking two amino acids, or protein building blocks, near the place where the enzyme attaches to its target molecule. Such a bond had not previously been observed in laccases by scientists.

Dr. Škerlová speculated that this bond keeps the enzyme rigid and stable. It may in fact prepare blue laccase BP76 for the lethal role it has to play.

“It has to be able to react very fast,” she said. Perhaps without this stabilizing bond, the explosive reaction would fizzle out.

There may be other peculiarities that allow termites to live with an enzyme strapped to their backs that could kill them at any moment. When a worker is young, Dr. Škerlová explained, and it still has plenty of labor to contribute to the colony, it has very little of the enzyme in the pockets on its back. The colony is not ready to do without younger insects.

But as time passes, and a worker’s mandibles wear down, the enzyme builds up, little by little. The oldest termite workers can be identified by the blue packets of death-dealing enzyme that have accrued over their lifetimes on their backs, a sign of their readiness to die for the good of the nest.