Analysing the fecal sample from Belgium for its viral components, researchers found a range of phages - viruses that infect bacteria.
The viruses in the fecal sample are phages rather than infecting eukaryotic organisms such as animals, plants, and fungi.
Most of the viral sequences the researchers found in the ancient coprolite (fossil fecal sample) were related to viruses currently known to infect bacteria commonly found in stools (and hence, in the human gastrointestinal tract).
These included both bacteria that live harmlessly, and even helpfully in the human gut, and human pathogens, said corresponding author Christelle Desnues of Aix Marseille Universite in France.
The communities of phage within the coprolite were different, taxonomically, from those seen within modern human fecal samples, but the functions they carry out appear to be conserved, said Desnues.
The finding reinforces the hypothesis that the viral community plays a fundamental role within the human gastrointestinal tract, and one which remains unchanged after centuries, even while the human diet and other human conditions have been changing, researchers said.
Over the last five years, considerable evidence has emerged that bacteria inhabiting the gut play an important role in maintaining human health, for example, as part of the human metabolic system, said Desnues.
Her own research suggests that bacteriophage infecting the gut bacteria may help maintain these bacteria. Among the genes found in the phage are antibiotic resistance genes and genes for resistance to toxic compounds.
Both toxins and antibiotics are common in nature, and Desnues suggests that the resistance genes may simply be protecting the gut bacteria from them.
"Our evidence demonstrates that bacteriophages represent an ancient reservoir of resistance genes and that this dates at least as far back as the Middle Ages," said Desnues.
"We were interested in viruses because these are 100 times more abundant than human cells in our bodies, but their diversity is still largely unexplored," said Desnues.
The study was published in the journal Applied and Environmental Microbiology.