Revealing human impact on natural ecosystems through soil bacterial DNA sampled from a 1,500-year-old archaeological site

For millennia, human activities have affected the surrounding natural ecosystems including belowground microorganisms. Their short- and medium-term effects on the diversity and the composition of soil microbial communities are well documented, but their lasting effects remain unknown. When unoccupied for centuries, archaeological sites are appropriate for studying the long-term effects of the past human occupancy on natural ecosystems, including the soil compartment. In this work, the soil chemical and bacterial compositions were compared between the Roman fort of Hegra (Saudi Arabia) abandoned for 1,500 years, and a preserved area located at 120 meters of the southern wall of the Roman fort where no human occupancy was detected. We show that the four centuries of human occupancy has deeply and lastingly modified both the soil chemical and bacterial compositions inside the Roman fort. We also highlight different bacterial putative functions between the two area, notably associated with the human occupancy. Finally, this work shows that the use of soils from archaeological sites cause little disruption and can bring relevant information, at a large scale, during the initial surveys of archaeological sites.