A cadaver is far from dead when viewed as an ecosystem for a suite of bacteria, insects, and fungi, many of which are obligate and documented only in such a context. Decomposition is a mosaic system with an intimate association between biotic factors (i.e., the individuality of the cadaver, intrinsic and extrinsic bacteria and other microbes, and insects) and abiotic factors (i.e., weather, climate, and humidity) and therefore a function of a specific ecological scenario.
Bacteria are often credited as a major driving force for the process of decomposition but few studies cataloging the microbiome of decomposition have been published. Much of the literature focuses on investigations of microbial activity in grave soils and has demonstrated that bacteria are useful biomarkers for forensics.
Currently, Sibyl Bucheli and I received a grant from the National Institute of Justice that aims to identify bacterial communities associated with decomposition of the human body (both internally and externally) as a possible forensic tool. Through the Southeast Texas Applied Forensic Science (STAFS) facility, we are able to place donated human cadavers outside to decompose in a natural setting and then collect a variety of samples as the body decomposes, which allows us to study decomposition in a very systematic manner. In our study, we swab various body locations to collect bacteria which will be analyzed by metagenomic techniques using next-generation sequencing technology in collaboration with Dr. Joseph Petrosino (Director of the Alkek Center for Metagenomic and Microbiome Research Center at Baylor College of Medicine), as well as collect and identify gases emanating from the body (in collaboration with Dr. Donovan Haines at Sam Houston State University and Dr. Matthew Ward at Daemen College), and collect insects colonizing the body. Preliminary data indicates that the bacterial communities do shift dramatically over time. We are also interested in identifying potential sources and sinks of the bacterial community as time progresses by looking at the bacterial communities found in the soil surrounding the body and how it changes over time (in collaboration with Dr. Rob Knight’s group at University of Colorado-Boulder) or by determining the microbiome of colonizing insects. In the end, we hope to come up with a cumulative systems approach to look at decomposition in a way that might complement existing forensic models at determining the postmortem interval.
Beyond the scope of work for the NIJ grant, we are also interested in looking at how abiotic factors influence decomposition. We are currently working in collaboration with Dr. Craig Glennie from the University of Houston to use terrestrial laser scanning (such as LiDAR) to develop models for calculating how much solar irradiance different areas of the body may receive and to develop models to calculate gross morphological changes during the decompositional process. These models may complement our work on determining the bacterial community structure of decomposition by helping explain why different bacterial communities are found at different areas of the body at the same time point (due to different amounts of solar irradiance different areas of the body receive) or by correlating community structure over time with gross morphological measurements (e.g. certain bacterial communities may be present before or after a body bloats).