Soil fungal and nematode community changes as a methodology for determining long-term postmortem interval after cadaver mass loss

Microbes thrive on the material resulting from the decomposition of the human body. The variation of the types and maturity of the microbes found in the soil in proximity to human remains have promise as a means of determining the time of death. The applicant proposes to combine cutting-edge molecular techniques and classical microscopic techniques to extend the timeframes over which this approach could be used to estimate the time of death. Research to date has focused on fairly short timeframes.

"Note: This project contains a research and/or development component, as defined in applicable law," and complies with Part 200 Uniform Requirements - 2 CFR 200.210(a)(14).

nca/ncf

The determination of the postmortem interval (PMI) is a fundamental necessity in forensic investigation and the accuracy of its assessment is critical. Decomposition is a dynamic process, reliant upon a suite of largely environmental parameters, which serves to create a need for multiple PMI methodologies with some degree of redundancy to successfully address this considerable variability.

Recent work exploring microbial bacterial succession of decomposition products in the soil has shown great promise as another methodology for the determination of short-term PMI. However, numerous microbial changes occur in the soil environment extending for months after active decomposition has finished, and study dedicated to this timeframe is virtually nonexistent.

This research proposal is based upon the following: that fungal colonies have been anecdotally observed to appear very late in the decomposition process, and that soil nematode communities undergo population shifts due to soil nutrient availabilities and can serve as indicator organisms for soil quality. Both nematodes and fungi are part of the soil eukaryotic decomposing community, and while studied in conjunction with leaf litter, have received little association with vertebrate decomposition. Given that decomposition environments have strong modulating effects on the bacterial communities present with the cadaver and the soil, it is therefore our hypothesis that these factors will also have a strong effect on the soil fungal and nematode populations inhabiting this area, and that these population changes are shifted toward primarily later time periods.

Further, as the soil environment gradually recovers from a decomposition event, these respective population shifts can serve as unique time markers for the determination of the PMI. Our study is designed to integrate cutting-edge molecular techniques with classical microscopic techniques to create quantitative means whereby PMI can be determined for extended periods after a decomposition event. This has the capability for immediate application to the criminal investigators' repertoire, as well as the virtue of employing techniques that are less likely the strain the already tight budgets of local forensic laboratories.

Most importantly, this research stands to expand the investigators' ability to formulate concrete lines of evidence in situations where victims of foul play are recovered at later intervals or in situations where it may not be possible to reach victims in a timely manner.

ca/ncf