Fungal succession during mammalian cadaver decomposition and potential forensic implications

Abstract

The necrobiome is the postmortem community that includes bacteria, fungi, arthropods, and other cadaver-associated organisms. It has been suggested as biological evidence for forensic investigation. Fungi form distinctive mildew spots in colonizing decomposing bodies, converting them into moldy cadavers. However, the postmortem fungal community consists of more than these visible species. Characterizing the succession pattern of the fungal community during decomposition is valuable not only for understanding the ecosystem composition of the cadaver decomposition islands but also for contributing to forensic investigations. In the present study, the fungal composition of pig cadavers and succession patterns during decomposition were investigated with high-throughput sequencing. The succession patterns were easier to discern in outdoor cadavers, compared with those that were placed indoors. The metabarcoding approach revealed trends linking particular fungal taxa with specific postmortem intervals (PMIs). Dominant species increased notably in cadavers and soil. Furthermore, the succession of the soil community was driven by the cadaver decomposition. Significant mycoflora differences were observed between environmental and cadaveric soil. The results obtained suggested that postputrefaction mycoflora have considerable potential for PMI estimation, particularly in cases that involve heavily decomposed bodies. In addition, the diversity of fungal communities revealed by the metabarcoding approach allowed us to discriminate the sites of cadaver decomposition, implying that postputrefaction mycoflora may be helpful in identifying the environment in which a cadaver has been placed, or the original location from which a cadaver has been moved. Our results provide an important step towards developing fungal evidence for use in forensic science and add to the growing body of work on postmortem microbial communities.

Soil Fungal Communities Investigated by Metabarcoding within Simulated Forensic Burial Contexts

“…These findings could suggest that the cadaveric soil is not a favourable environment for the survival and for the growth of the fungi introduced with the carcass, and that overall the fungi introduced into the soil by the body are replaced by soil fungi in less than two months. This finding is also in accordance with what found by Fu et al [23], where the variety of soil fungi present after one-day post-mortem was higher than that found during the decomposition of the carcasses. In particular,…”

“…Unfortunately, the very limited amount of metabarcoding data available on fungal communities associated with the cadaveric decomposition did not allow us to perform a comprehensive comparison between different studies. However, we found some similarities both with the study conducted by Metcalf et al [32] on human cadavers in Texas, with the one conducted by Fu et al [44] on rat carcasses in China and with the following study conducted by the same group on exposed pigs [23], despite in all cases, they were conducted with exposed remains instead of with buried ones as in our study. Overall we can state that the fungal succession during the various decomposition stages appears reproducible and reliable despite different geographical areas, different animal carcasses and different post-mortem conditions (e.g.…”

“…1B) and allowed for a better discrimination between the various time points than Library A. Results showed an overall decrease in richness of the fungal population with increasing PMIs within both libraries, and this is similar to what we have already found for soil bacteria [19] and to what found by Fu et al [23] in soil underneath decomposing exposed pigs. This suggests that the presence of a decomposing carcass has a negative impact on the diversity of the fungal communities present in the soil, and the effect is particularly exacerbated when the body reaches the putrefaction/liquefaction stage of decomposition where the least richness has been recorded.…”

“…Abundance of Melanommataceae, Bionectriaceae, Massarinaceae, Onygenaceae Pseudeurotiaceae, Coniochaetaceae, Gymnoascaceae, Chaetomiaceae and Nectriaceae on the other side showed a decline in P2, P3 and P4 compared with the control, indicating that the gravesoil environmental composition negatively affected their survival.Ascomycota are decomposers able to break down the animal tissues into major organic compounds, and they have already been identified as fungal decomposers particularly active during the active decay of the carcass[32]. The increase of the abundance of Ascomycota during the first stages of decomposition was not reported by Fu et al[23] within soil collected underneath exposed pig cadavers, and may be specific to buried cadavers.Basidiomycota showed a constant decrease in their abundance starting from a higher amount and variety of families in control samples and ending in a significantly lower amount with prolonged PMIs.…”

“…Fu et al performed metabarcoding analyses of the fungal communities associated with the decomposition of rat carcasses [22] and more recently of juvenile pigs both exposed in outdoor conditions (in China, during the summer period, sampling was performed from day 0 to day 14 postmortem) and left to decompose indoors [23] as a proxy to estimate PMI from the fungal shift. They found trends between specific decomposition stages and specific fungal taxa, suggesting potential for this type of analysis to estimate PMI.…”