Ancient microbial DNA and proteins preserve in concretions covering human remains

Archaeological remains covered with concretions, including human bones, are commonly found in certain areas and time periods of interest for understanding the past, but have yet to be investigated for potential ancient DNA (aDNA) and protein content. We extracted aDNA and proteins in tandem from human dental remains and their surrounding concretions and compared them to non-concreted human dental remains from the same site. Concretions appeared homogeneous in color and texture, consisting of a hard dark gray sediment adhered to the bone surfaces, presumably as a result of cyclical waterlogging of the burial deposits. Concretions were found to contain human oral microbial genomes and proteins, probably leached from the original skeletal source, as well as environmental and human proteins. Despite this, both the original teeth and the concretions surrounding them lacked endogenous human aDNA, indicating that the use of this type of material in future molecular archaeological applications is limited.