Microbial composition of archaeological middens: tracing human footprints through centuries in Greenland's ancient...

The history of Greenland is marked by different waves of Paleo-Inuit immigration from North America from 2,500 BC to the 12th century and from the 10th to 15th century, Norse settlers immigrated from Northwest Europe and flourished in Southwest Greenland with the introduction of domestic livestock. The different Inuit and Norse cultures created middens by dumping and accumulating domestic waste; a latent source of microbes, including potential pathogens, that might have been preserved due to the general wet and cold conditions in the region. The aim of this study was to evaluate whether ancient Arctic settlements might be possible hot-spots for pathogenic agents that may spread to the surrounding environment because of current climate changes. Using metagenomics, we compared the microbial communities and resistomes of 78 samples from middens from different ages and locations in West and South Greenland (two Paleo-Inuit, four Norse and one early Colonial-time middens) to 143 soil samples from nearby surroundings. We found that the middens harbor a distinctive microbial signature enriched in human-associated bacteria. Those include opportunistic pathogens such as Clostridium perfringens and Paeniclostridium sordellii. In some early colonial midden layers, C. perfringens and Paraclostridium tenue together accounted for up to ~40%-50% of MetaPhlAn-derived relative abundance in individual samples. Antimicrobial resistance genes representing 17 resistance classes were detected across all sites, dominated by β-lactam and tetracycline resistance. Transect analyses across an actively eroding midden showed that midden-derived bacteria were confined to local erosion layers and were rapidly replaced by native marine communities, indicating limited environmental dispersal.