Single-celled organisms called archaea occupy their own branch on the tree of life, like bacteria, but we know a lot less about them. Like bacteria, archaea also don't have a nucleus, and have colonized many of the world's environments, including the insides of animals, but their genomes are different from bacteria, and no pathogenic archaea have been identified, yet. Researchers have now learned a bit more about archaea that live in the guts of vertebrates. This work, which was reported in Nature Microbiology, has shown that these mysterious microbes are far more diverse than we thought, and that this diversity is influenced by animal relationships.
The gastrointestinal system of most animals carries a colony of microbes known as the gut microbiome. Trillions of organisms are thought to live in the human gut microbiome, which has a powerful influence on our health. Microbes in the gut microbiome also influence each other. For example, we know that archaea can produce methane as they take up chemicals that are produced during bacterial fermentation.
"We were amazed by the specificity but also diversity of the archaeal species we found in the gut of vertebrates. Among them was the archaeon Methanothermobacter," noted lead study author Nicholas Youngblut of the Max Planck Institute for Developmental Biology.
The researchers were surprised to find Methanothermobacter because it has only been found growing in hot places that around around 60 degrees Celsius. "We saw the archaeal genus [was] particularly common and widespread among birds, which may be due to their higher body temperature of about 40 degrees Celsius or warmer," he added.
In this study, the researchers also tried to collect samples from species that live in the wild to get a more accurate picture of archaea in the microbiome; the microbiome of animals is known to be affected by captivity.
"Three-quarters of the samples we examined, which were collected with the support of the University of Veterinary Medicine Vienna, came from wild animals," said study co-author Georg Reischer of the Vienna University of Technology's Water and Health Research Center and ICC Water & Health. "This is unique and provides us with a comprehensive picture."
Previous work by this team has suggested that some gutnarchaea can be inherited, and that human genetics may influence gut microbiome diversity. This work has expanded that idea to other animals, and suggested that related species carry more similar types of archaea.