Researchers working knee-deep in 14th- and 15th-century latrines have found that bacterial DNA from human excrement can last for centuries and provide clues to how our gut contents have changed significantly since medieval times.
Analysis of two cesspits, one in Jerusalem and the other in the Latvian capital, Riga, could help scientists understand if changes to our microbiome – the genetic makeup of the bacteria, virus, fungi, parasites and other microbes living inside us – affect modern-day afflictions.
“At the outset, we weren’t sure if molecular signatures of gut contents would survive in the latrines over hundreds of years,” said Kirsten Bos, a specialist in ancient bacterial DNA from the Max Planck Institute for the Science of Human History and co-leader of the study.
“Many of our successes in ancient bacterial retrieval thus far have come from calcified tissues like bones and dental calculus, which offer very different preservation conditions.”
One of the big challenges in working with an archaeological dig was differentiating what was faeces and what was dirt. However, researchers were able to identify a wide range of bacteria, parasitic worms, and other organisms known to inhabit the intestines of humans.
They choose latrines believed to have been used by many people in an attempt to gather insight into the intestinal flora of whole communities. The study, published in Philosophical Transactions of the Royal Society B, found the microbial content of the medieval poop was unique from modern humans, including those who lived hunter-gatherer lifestyles.
“It seems latrines are indeed valuable sources for both microscopic and molecular information,” Bos said. “We’ll need many more studies at other archaeological sites and time periods to fully understand how the microbiome changed in human groups over time.
“However, we have taken a key step in showing that DNA recovery of ancient intestinal contents from past latrines can work.”
Piers Mitchell, a paleopathologist at Cambridge University who worked on the study, said ancient latrines could become a key source of biomolecular information and allow scientists to explain how modern lifestyles affect human health.
“If we are to determine what constitutes a healthy microbiome for modern people, we should start looking at the microbiomes of our ancestors who lived before antibiotic use, fast food, and the other trappings of industrialisation,” he said.