Bee microbiome fights parasites with cyanide

Our guts are crammed with microbes; in fact some say that we’re passengers in our own bodies, outnumbered in cellular terms by our own microbiomes. We know that these microorganisms are crucial for good health. They access and liberate micronutrients in our food that we can’t; they suppress the growth of pathogens; they’re involved with the regulation of the immune system, and even talk to the nervous system. In recent years we’ve also realised that they may even be detoxifying our diet and breaking down potential poisons before they can be absorbed. And other animals are no different, including the humble honeybee. Speaking with Chris Smith, Erick Motta, at the University of Texas at Austin, has been studying how the bee microbiome can make use of and even weaponise potential dietary toxins, like the cyanide-containing amygdalin bees pick up in almond pollen, to fight off parasites…

Erick - I work with good microbes and I use honeybees as a model to investigate how they can play a role. Basically break down components from the diet, which sometimes can be toxic to animals. And this seems to be the case for some specific plant toxins that we may get from our diet.

Chris - Are honeybees particularly vulnerable to this effect?

Erick - Yeah, so that's the great question here because we don't really know what happens once they metabolize these kinds of toxins. I have studied one specific toxin that honeybees they may face in the environment. The name is amygdalin. So this is a plant toxin found in almonds. Amygdalin by itself is not toxic, but when it's broken down, when it's metabolised, then it can release a specific toxic molecules that can provide a detrimental effect to the animal.

Chris - It's a precursor to making cyanide, isn't it, amygdalin that the almonds make? Yes. What what did you do then to investigate how this is and isn't produced in the gut?

Erick - We use honeybees without microbes in the gut. So to investigate whether or not the bee was playing a role in this degradation, we had these two main groups of bees, one group, the bees, they basically didn't have any microbes in the gut. And the other group, we allowed them to acquire these microbes by interacting with all the bees from the hive because that's how they acquired these microbes by social interaction. We exposed them to this plant toxin to see how it would be metabolised in the gut. And we found that whenever the microbes were there we wouldn't detect intermediates: byproducts from amygdalin degradation as we would see in bees with the microbes.

Chris - Does that tell you then that the bees do some of the breaking down and the microbes do the rest of the breaking down and they get rid of those potentially toxic intermediates? The microbes are doing that job and without the microbes, the bees would effectively be poisoned by those accumulating degradation products?

Erick - Yeah, so it's kind of going to this direction but we don't really know how much those byproducts they can be toxic. So right now the what we know it's that the microbes, they can fully metabolise amygdalin and it can release hydrogen cyanide, which is this toxic molecule. But based on the exposure levels, how much they are basically consuming from amygdalin, this doesn't seem to give a detrimental effect to this. So we believe that there may be another component going on here, which means that those toxic molecules being released, they may help these actually fight specific parasites because other studies they have shown that amygdalin exposure whenever bees, they are fed on amygdalin, actually they don't have much parasites proliferating in their guts.

Chris - But in the absence of the microbes, if the bees break it down to an intermediate, what happens to that intermediate? Does that build up and does that poison the bee? Yeah, so it does need the microbes to get rid of it. Is that the case?

Erick - Yeah, so whenever they don't have the microbes, some specific intermediates, they're gonna accumulate, but we don't know how toxic they are. And probably it's gonna be a matter of concentration. So if it gets accumulated in the gut, that may bring some detrimental effect to bees. But this deserve further investigation.

Chris - It's intriguing this though, isn't it, because the bees are basically using microbes to break down something that might be toxic, save them from a, a potentially toxic effect of an intermediate and in the process weaponise it to get rid of another nasty!

Erick - Yeah, that's true. Yeah. So sometimes it's hard to predict the consequences of metabolising the toxin because the byproducts may be even more toxic or may be not toxic. So it's just a matter of like what's being produced and the concentration that it's being produced in the gut. So in this case, what do we know is that both the host and the microbes, they play a role integrating amygdalin and this leads to the production of hydrogen cyanide. Initially we thought this would be bad for the bees, but it seems that based on the levels that they can be exposed when they're pollinating almond trees, it's not the case because they still keep going there and actually honeybees, they are the exclusive pollinator for almond trees. So the thing here is why this is happening and we believe there are like potential benefits to this especially in parasite prevention, but this needs to be proven yet.