Abstract
Small organic molecules, lipids, proteins, and DNA fragments can remain stable over centuries. Powerful and sensitive chemical analysis can therefore be used to characterize ancient remains for classical archaeological studies. This bio-ecological dimension of archaeology can contribute knowledge about several aspects of ancient life, including social organization, daily habits, nutrition, and food storage. Faecal remains (i.e. coprolites) are particularly interesting in this regard, with scientists seeking to identify new faecal markers. Here, we report the analysis of faecal samples from modern-day humans and faecal samples from a discharge pit on the site of the ruins of ancient Pompeii. We propose that bile acids and their gut microbiota oxo-metabolites are the most specific steroid markers for detecting faecal inputs. This is due to their extreme chemical stability and their exclusive occurrence in vertebrate faeces, compared to other ubiquitous sterols and steroids.
Highlights
Small organic molecules, lipids, proteins, and DNA fragments can remain stable over centuries
The analytical method was based on high-performance liquid chromatography (LC), coupled online to electrospray mass spectrometry (ESI–MS), for the simultaneous determination of 27 bile acids (BAs), including 21 oxo-BAs that are potentially present in vertebrate faeces and synthesized by gut microbiota enzymes
Our abbreviations for oxo-BAs reflect the structure of the respective metabolic precursor, indicating the position involved in the oxidative reaction (i.e. ‘3oxo lithocholic acid (LCA)’ means ‘LCA with a hydroxy group converted to a carbonylic group at position 3 of the steroid ring’)
Summary
Lipids, proteins, and DNA fragments can remain stable over centuries. We propose that bile acids and their gut microbiota oxo-metabolites are the most specific steroid markers for detecting faecal inputs. This is due to their extreme chemical stability and their exclusive occurrence in vertebrate faeces, compared to other ubiquitous sterols and steroids. Sterols occur ubiquitously in plants and animal deposits (e.g. root exudates, micro fauna and faeces) and in soils (being produced by soil microorganisms) This ubiquity drastically reduces their specificity as an indicator of a human origin. BAs are likely the most specific steroid markers for determining the origin of a faecal input This is because they occur exclusively in vertebrate faeces and other biological fluids (e.g. bile and blood). BAs and oxo-metabolites are very important for the growing field of bioarcheology due to their stability and specificity (they are present in vertebrate faeces only and are species-specific)
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