Postmortem Submersion Interval (PMSI) Estimation from the Microbiome of Sus scrofa Bone in a Freshwater Lake

Estimating the postmortem submersion interval (PMSI) is an important step in providing investigative leads for bodies recovered from aquatic environments. While many studies have developed microbial succession-based models for the prediction of postmortem interval (PMI) in terrestrial systems, similar well-replicated long-term decomposition studies are lacking for aquatic systems. Therefore, this study sought to identify temporal changes in bacterial community structure associated with porcine skeletal remains (N=200) for an extended period (5200 Accumulated Degree Days (ADD) / 579 Days) in a fresh water lake. Every ca. 250 ADD, one cage, containing 5 ribs and 5 scapulae, was removed from the lake for a total of nineteen collections. Water was also sampled at each interval. Variable region 4 (V4) of 16S rDNA was amplified and sequenced for all collected samples using Illumina MiSeq FGx Sequencing platform, resulting data was analyzed with the mothur (v1.39.5) and R (v3.6.0). Bacterial communities associated with ribs differed significantly from those associated with scapulae. This difference was mainly attributed to Clostridia, Holophagae and Spirochaete relative abundances. For each bone type, a-diversity increased with ADD; similarly, ß-diversity bacterial community structure changed significantly with ADD. Furthermore, ß-diversity changes were explained using environmental parameters and inferred functional pathways. Models fit using family-level taxa outperformed those fit with class-level taxa and scapula samples outperformed models fit with rib samples. The models using 24 rib and 34 scapula family-level taxa allowed the prediction of PMSI with root mean square error of 522.97 ADD (~57 days) and 333.8 ADD (~37 days), respectively.