Contribution of Host and Environmental Microbes in the Decomposition Process

The postmortem interval (PMI) is one of the most challenging pieces of evidence to obtain in the field of forensic science. In recent years, a novel approach for estimating PMI has been developed based on predictable patterns in microbial community progression found in both mouse models and human cadavers. However, it is unknown if factors that contribute to the composition of the host microbiome (e.g. drug and antibiotic use, immune deficiency, and diet) impact this model’s predictive ability. In the current study, we utilized specific pathogen free (SPF), and germ-free (GF) mice buried in non-sterile and sterile graves to identify sources of variability in microbial community progression. Intestinal contents were collected over the course of a 21-day decomposition period, and bacterial communities were then identified by 16S rRNA sequencing. We found that GF mice remained sterile over the study period, regardless of soil sterility. In contrast, soil sterility had an impact on microbial community dynamics in SPF mice. These data suggest that microbial communities at the time of death influence the entry of environmental microbes and microbial progression. Together, these results show that differences in the host microbiome at the time of death can significantly impact the predictive power of microbial succession in calculating PMI and should be taken into consideration when developing future models