Histological and metagenomic analysis of microbial communities in archaeological human bones

Buried archaeological bones tend to be heavily degraded by microorganisms. This type of biodegradation was already identified in the 19th century and remains a subject of continuous investigation. However, the underlying processes are still not fully understood, and the organisms responsible for the decay have not been clearly identified. Technological advances in genetic sequencing now allow detailed study of the bone microbiome. And yet, identifying the species causing the observed bioerosion has proven challenging. Relatively few studies have combined the investigation of bone degradation by microscopy, so-called histotaphonomy, with metagenomic analyses. This study aims to bridge this gap. We utilize a large set of human bone samples from medieval cemeteries in south-western Norway. Detailed microscopic analyses have been carried out, showing diverse levels of preservation. The extent of bioerosion is correlated with the results from metagenomic analyses as well as environmental factors. Microbiome diversity is greater and more evenly distributed in well-preserved bones with limited bioerosion, particularly those recovered from burials beneath church floors, contrasting with outdoor cemeteries. Fungal taxa were detected in only a single sample in the metagenomic data despite histological evidence of fungal structures, and their role in bone bioerosion remains unclear. Our findings show that preservation state is strongly associated with microbiome composition. The most prevalent genus found was Streptomyces, supporting previous research suggesting that bacteria within this group could be involved in bone bioerosion.