Postmortem Interval Estimation Based on Eukaryotic Community Associated with Soil Under Decomposing Porcine Remains

Recent studies have shown that bacteria associated with soils under a carcass change significantly both temporally and spatially. These studies were done in both laboratory and field conditions, but with limited replications. In addition, limited information exists on temporal and spatial changes in eukaryotic community structure associated with soil under decomposing remains. This study was designed to fill in these gaps and expand on previous studies to improve postmortem interval (PMI) estimation techniques as well as to identify cadaver decomposition islands (CDI) based on eukaryotic community structure associated with soil under vertebrate remains. To accomplish this goal, soil samples were collected at 0 m (beneath the carcass ) and 3 m away (control) from the porcine carcasses (N=6) on day 1 (T1/27 accumulated degree day (ADD)), day 2 (T2/57 ADD), day 26 (T26/734 ADD), day 33 (T33/930 ADD), day 40 (T40/1130 ADD), day 47 (T47/ 1326 ADD), day 54 (T54/ 1516 ADD), and Day 61 (T61/1703 ADD) . The eukaryotic community for each sample was determined using 18S rDNA dual-index MiSeq sequencing on MiSeq FGx sequencing platform. Sequence data were analyzed using Mothur v1.39.5 and in RStudio. Results showed significant differences in eukaryotic community structure between soil collected under the carcass (0 m) and at 3 m away (control), but the same was not true for 0 m soil samples collected at different time points/ADD. The spatial difference in eukaryotic community composition was mainly due to decreased relative abundance of Nematoda (e.g., Ascaridida and Araeolaimida) and increased relative abundances of Basidiomycota (e.g., Trichosporonaceae) and Ascomycota (e.g., Dipodascaceae). During initial period of decomposition (0-57 ADD), eukaryotic phylogenetic diversity did not differ much between soil under the carcass (i.e., 0 m) and the control site (i.e., 3 m away) but after 57 ADD, eukaryotic α-diversity declined sharply in soil under the carcass but remained unchanged in control soil. In conclusion, soil eukaryotes associated with decomposing porcine remains significantly differ spatially but not temporally. These results highlight the importance of the microbial eukaryote community during the process of decomposition and in the identification of CDI