NEW YORK (GenomeWeb) – Microbes deemed pathogenic to many vertebrate species appear to make up a large proportion of the vulture's gut microbial community, according to a new study in Nature Communications.
Researchers from the Smithsonian Institute, the University of Copenhagen, Aarhus University, and elsewhere used a combination of 16S ribosomal RNA sequencing and deep metagenomic sequencing to look at gut microbiomes from 50 New World vultures from the black vulture or turkey vulture species. Compared to the microbial communities present on the birds' faces, they found a distinct lack of diversity in the vulture gut microbiomes.
The team's follow-up analyses indicated that the acidic environment in the vulture gut dissuades all but a few hearty bugs from setting up shop. But the bacteria that do survive in that selective setting — many of them acquired by inadvertently consuming carrion feces — appear to contribute to the birds' digestive capabilities.
"Our results show there has been strong adaptation in vultures when it comes to dealing with the toxic bacteria they digest," the study's first author Michael Roggenbuck, a doctoral student at the University of Copenhagen, said in a statement.
"On one hand vultures have developed an extremely tough digestive system, which simply acts to destroy the majority of the dangerous bacteria they ingest," Roggenbuck explained. "On the other hand, vultures also appear to have developed a tolerance towards some of the deadly bacteria — species that would kill other animals actively seem to flourish in the vulture lower intestine."
Vultures are noted for their ability to feast on dead flesh that would lay most vertebrates low with severe food poisoning, due to the decay associated with the food itself as well as its frequent fecal contamination.
The researchers decided to turn to metagenomic sequencing in an effort to understand vultures' ability to "survive eating this putrid cocktail," co-senior author Lars Hansen, an environmental sciences researcher at Aarhus University, said in a statement.
The researchers decided to turn to metagenomic sequencing in an effort to understand vultures' ability to "survive eating this putrid cocktail."
To that end, the team collected facial skin swabs and large intestine samples from 26 black vultures and 24 turkey vultures sampled from the wild. They also tested fecal samples from several captive-bred birds, including two turkey vultures, an Amazon parrot, an American flamingo, a red-tailed hawk, an African-spotted owl, and a red-legged seriema.
Along with Roche 454 sequencing of amplified 16S rRNA gene sequences from the facial swabs, researchers used Illumina instruments to conduct metagenomic sequencing on the complete collections of microbial DNA present in hindgut and fecal samples.
The team used 16S sequences to get a glimpse at the types of mammal meat the wild vultures had consumed as well as the microbes they'd been exposed to in the process.
In those experiments and in analyses of gut microbes, the researchers found similarities between the black vulture and turkey vulture species. But there were pronounced differences when comparing the microbes present on the birds' faces to those in their hindguts.
The microbial communities identified with vulture facial swab samples contained representatives from almost 530 operational taxonomic units, on average. In contrast, members of just 76 OTUs turned up in the average vulture gut microbiome.
Moreover, microbial communities in the vultures' gut samples tended to be dominated by representatives from the Clostridia class and the Fusobacteria phylum, which are relatively common in soil samples, but tend to get flagged as potential pathogens when detected in vertebrates.
The same Clostridia and Fusobacteria bugs were found on facial skin swabs from the birds, consistent with the notion that they were exposed to these microbes while scarfing down carrion.
Interestingly, microbial sequences in fecal samples collected from turkey vultures living in a zoo largely overlapped with those detected in the wild vultures' hindguts, researchers reported, but differed from gut microbial communities found in other predatory birds such as hawks and owls.
"[T]he most likely scenario is that Clostridia and Fusobacteria outcompete other bacterial groups in the anaerobic hindgut, and that vultures benefit from the bacterial breakdown of carrion while tolerating bacterial toxins," the researchers concluded. "Some scavenging birds are known to harbor antibodies against toxins such as botulinum and we speculate that vultures are unusually tolerant of toxins."