Bacteria in the mouth and how they evolved

The bacteria in the mouth and the plaque on our teeth contain surprising clues about the evolution of the first hominids and our own health.

In this way, our oral microbiome, which is made up of trillions of microbial cells belonging to thousands of bacterial species, has evolved together with us over millions of years. However, we still know very little about him.

A group of scientists, from more than 40 institutions in 13 countries, has studied the human and neanderthal fossilized dental plaque to learn about the evolutionary history of the hominin oral microbiome in the last hundred thousand years.

Likewise, he has compared these remains with that of chimpanzees, gorillas and howler monkeys. The results are published in the journal Proceedings of the National Academy of Sciences (PNAS).

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Bacteria in the mouth

“The study of the microbiome through metagenomics is a fundamental task to understand the evolution of our species and the functioning of our body,” he says. James Fellows Yates, a researcher at the Max Planck Institute for the History of Science in Germany, who is leading this work in which several Spanish research centers also participate.

According to the authors, this work highlights the value of investigating ancient oral metagenomes to reveal key insights into major events in modern human evolution and prehistory.

“A metagenome corresponds to the total genetic content of a sample. Not just the DNA of the host, but also of all the microbes that live in the body – the human microbiome. This is considered as important for human health as a vital organ such as the heart or lungs, since maintaining a healthy set of microbes means that we maintain our own body ”, says the scientist.

In total, they analyzed 124 fossil remains that revealed 10 bacterial genera that have persisted throughout the evolution of African hominins and are also shared with howler monkeys.

This fact suggests that these microbial groups could have played a key role in dental plaques for more than 40 million years.

The authors also found important differences in Homo bacteria and chimpanzees, but striking similarities between Neanderthals and modern humans.

In fact, the oral bacteria of modern humans and Neanderthals are almost indistinguishable.

“That these bacteria in our mouths and theirs are so similar supports the evidence that we have had a very long and close relationship with them,” adds Fellows Yates.

Consumption of foods rich in starch

The most striking thing about this finding is that they have discovered a group of bacteria, present in both modern humans and Neanderthals, that are specially adapted to consume starch.

“Unlike non-human primates, Homo is characterized by the abundance of Streptococcus species that can produce proteins that bind to the enzyme amylase, which helps convert starch into sugars. This finding suggests that these microbes adapted to starch-rich diets early in human evolution, “the researchers note.

However, they also found some small differences, such as that ancient humans living in Ice Age Europe shared some bacterial strains with Neanderthals, although these strains are no longer present in humans today.

“The study uses the starchy foods referred to as ‘underground storage organs’ (USOs) that were consumed by early hominins, that is, starchy tubers such as yams in Africa,” explains the investigator.

Starchy foods, such as roots, tubers, and seeds, are rich sources of energy, and it had been argued that our ancestors’ transition to consuming these foods may have been what allowed humans to develop the large brains that characterize our species.

“Analyzing not only the genetics of the host, but perhaps also the genetics of the bacteria in our human microbiome will help determine exactly when these adaptations occurred,” says Fellows Yates.

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The Spanish contribution to the study

The so-called “Red Lady” from the Cueva del Mirón, in Ramales de la Victoria (Spain), a Magdalenian woman of about 19,000 years ago, is part of this study, as the only representative of the European Upper Paleolithic populations.

Of the nine new Neanderthal sites from the European Middle Paleolithic in this study, five are in Spain: Banyoles, La Güelga, the Valdegoba Cave, the Boquete de Zafarraya cave, and the Sima de las Palomas del Cabezo Gordo.

In addition, four individuals from the El Collado site were included as representatives of the Mesolithic period of the Iberian Peninsula.

“Working with DNA that is so old is a great challenge and, like archaeologists reconstructing broken vessels, archaeologists also have to painstakingly piece together the broken fragments of ancient genomes to reconstruct a complete picture of the past. To achieve this, we have developed new tools and analyzes to genetically characterize billions of DNA fragments in order to identify bacteria – long dead – that are preserved in the archaeological record ”, they conclude. (Eva Rodríguez, SINC AGENCY)

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