Microbes protect vultures from their toxic diet

The probiotics that allow vultures to eat carrion could inspire an alternative to antibiotics for farmed birds. Viviane Richter reports.

The intestines of the American New World vulture hold surprisingly few types of bacteria. – Mark Bowler/Getty Images

Vultures relish rotting meat but how do they survive the deadly bugs that infest their food? It seems they opt for the probiotic approach, enlisting good bacteria to ward off the bad, microbiologists at Aarhus University in Denmark discovered in a study published in Nature Communications.

The microbes on a rotting carcass produce toxins that deter most animals, but not vultures. On the contrary, vultures sniff out the whiff of decay, which makes it easier for the birds to rip through thick hides.

Biologists already knew some of the birds’ defences. Vultures urinate on their own legs to disinfect them, and vulture stomachs, which are 10 times more acidic than human stomachs, are harsh enough to kill most pathogens in rotting food. But some pathogens, such as Bacillus anthracis, can form protective spores to survive the acid. So the secret of the vulture’s iron gut must lie elsewhere.

The researchers set out to find it. They dissected American New World vultures and analysed the DNA from their large intestines. What they found – or rather didn’t find – was surprising. The human intestine contains hundreds of species of microbes. But the vultures boasted only two – Clostridia and Fusobacteria. That is even more remarkable given how many microbes cover the faces of the birds.

Clostridium reproduce rapidly, which may stop more toxic bacteria from gaining a foothold in the vultures' intestines. – SCIMAT/Getty Images

Why would these bacteria protect the vulture? One clue is that Clostridia reproduce quickly. While most bacteria take around 20 minutes, they take 6.3 minutes. The researchers suspect that the simple strategy is that these speedily reproducing bacteria stop the more toxic ones from gaining a foothold. And while Clostridia can themselves be toxic – in humans they cause food poisoning – the team suspect these are a benign variety. “We think that vultures possibly adopted these bacteria to detoxify the incoming community,” says Lars Hansen, who led the study.

Another clue to the vulture’s choice of resident bacteria is that Fusobacteria are very good at breaking down flesh. So this bug also pays its way by making nutrients more available.

The second of the dominant microbes in the vulture's gut is Fusobacterium, a bacterium that is good at breaking down flesh. – Science Photo Library/Getty images

And the strategy is inherited. Clostridia and Fusobacteria are passed from mother to chick rather than coming directly from the carcass meal. The researchers found the same bacteria in the guts of zoo vultures fed on non-rotting meat.

The vultures’ successful probiotic strategy suggests new approaches for farmed birds. Chickens for instance, are fed antibiotics to stop bacteria such as salmonella from spreading, but that creates the problem of antibiotic resistance in the entire food chain.

“Knowing how (and why) some bacteria keep other bacteria at bay may one day help us find effective alternatives to the antibiotics,” says David Topping, a bowel health expert at the CSIRO.

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