Mouse_Decomp_Forensics_2011_16S

Elucidating the time since death and locating clandestine graves are crucial in many forensic cases, but can often be a challenge. Biotic signatures of corpse decomposition, such as chemicals or the succession of insects, are commonly used to determine the post-mortem interval and to detect grave soil, but no method is successful in every scenario. Therefore, the development of new forensic tools is important. Microbes are ubiquitous in the environment and they play a key role in regulating the speed of decomposition. However, microbial communities are not currently utilized to their full potential as a forensic tool. Testing whether changes in microbial communities are predictable over the timeline of decomposition is crucial for assessing whether microbes can be used as a "biological clock" to assess time since death. Powered by advances in culture independent DNA methods and sequencing technologies, recent research has revealed that microbial communities are quantifiable and predictable across habitats such as the human mouth and skin and soil. Thus we performed a laboratory experiment leveraging new sequencing technologies to determine the temporal changes in corpse associated-microbes in which mice were allowed to decompose on soil at ambient temperature for up to 49 days. Samples from the abdominal cavity, skin and gravesoil were collected at regular intervals from 5 corpses per time point. Partial 16S and 18S ribosomal RNA genes were sequenced and computational pipelines were used to characterize the succession of bacterial and eukaryotic communities during the decomposition process. For each corpse-associated site, Proteobacteria increased over time, but most notably in the abdominal cavity, a site in which bacteria of the family Enterobacteriaceae dominated. Furthermore, the decrease in abundance of genera such as Bacteroides and Lactobacillus in the abdominal cavity over time lends support to the long-held hypothesis that decomposition in the abdomen shifts from anaerobes to aerobes or facultative anaerobes after corpse rupture occurs. Importantly, the microbial diversity of grave soil was significantly modified by corpse decomposition. Several genera from the families Enterobacteriaceae and Rhizobiaceae may be important indicators of grave soil. Eukaryotic sequence data revealed that nematodes of the family Rhabditidae dominate the meiofauna of both the corpse and soil during late stages of decomposition. Nematodes of the family Rhabditidae may also serve as an indicator of grave soil. We demonstrate that the vast, but measurable diversity of microbes has great potential for helping forensic scientists estimate the postmortem interval of corpses and locate clandestine gravesites.