Metabarcoding to investigate changes in soil microbial communities within forensic burial contexts

Noemi Procopio, Stefano Ghignone, Anna Williams, Andrew Chamberlain, Antonietta Mello, Michael Buckley

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    Abstract

    The estimation of the time elapsed since death (post-mortem interval, or PMI) is one of the key themes that forensic scientists have to address frequently. However, the estimation of PMI still suffers from poor accuracy and biases especially when decomposition stages are prolonged, so further improvements in methods for PMI estimation are desirable. Soil microbial communities associated with decomposing bodies have been shown to be good candidates for the estimation of the PMI of exposed bodies. Nevertheless, further research is required to better understand the bacterial succession associated with decomposition of buried carcasses in order to test its reliability and applicability for the estimation of PMI and to better understand the dynamics involved with decomposition within this particular scenario. Therefore we explored the succession of soil microbial communities associated with four decomposing pig carcasses (from one to six months PMI) using a metabarcoding approach. The sequencing of the bacterial 16S rRNA variable region 4 (V4) revealed trends linking particular microbial taxa with specific PMIs, and notably an increase in Proteobacteria, Firmicutes and Bacteroidetes at specific PMIs as well as a decrease in Acidobacteria. Our results, in accordance with previous studies conducted on exposed bodies of different mammalian species (including humans), also showed a general reduction of the taxonomic richness from two months PMI onwards, as well as an incomplete re-establishment of the starting soil microbial conditions after six months PMI. We also found specific mammal-derived taxa, such as Bacteroides spp., being still present in the soil after six months PMI. As such, this study serves as a baseline for additional research to allow the characterisation of biomarkers associated with specific PMIs. Due to the similarity between the results presented here and those reported in other types of decomposition studies we believe that the metabarcoding approach has considerable potential in the estimation of the PMI, particularly to clarify cases involving heavily skeletonised bodies or for the investigation of clandestine graves in which the carcass has been moved from its original place of deposition.

    Original languageEnglish
    Pages (from-to)73-85
    Number of pages13
    JournalForensic Science International: Genetics
    Volume39
    Early online date12 Dec 2018
    DOIs
    Publication statusPublished - 1 Mar 2019

    Keywords

    • 16S rRNA
    • Decomposition
    • Metabarcoding
    • Post-mortem interval
    • Taphonomy

    Research Beacons, Institutes and Platforms

    • Manchester Institute of Biotechnology

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