Microbial community analysis of human decomposition on soil

Abstract

Human decomposition is a complex process, involving a multitude of microbial species. Currently, little is known about the microbial species and processes that occur as cadavers decompose, particularly in outdoor environments. With the development of molecular ecology tools that allow the study of complex microbial communities, the 'black box' of the microbiology associated with decomposition is being opened. A preliminary study was performed to evaluate the changes in the soil bacterial and fungal communities that occur in response to human cadaver decomposition, and to assess the potential for using such changes in either of these two microbial communities for forensic time-since-death estimation. Terminal restriction fragment length polymorphism (T-RFLP) and phospholipid fatty acid (PLFA) analyses were performed on soil samples collected from beneath decomposing human cadavers at the University of Tennessee's Forensic Anthropology Centre. The soil fungal and bacterial communities showed significant changes in response to decomposition events, with some succession patterns emerging as decomposition progressed. Evidence of sequential changes occurring in the soil microbial community provides support for the idea that specific microbes could be used as time-since-death biomarkers, although major differences in the way replicate cadavers decomposed in this study suggested that both the bacterial and fungal communities may need to be considered to ensure such a method is forensically useful. Some difficulties were also encountered with the polymerase chain reaction (PCR) step in the T-RFLP method being inhibited by soil or decomposition compounds, which suggest that while DNA-based 'profiling' methods may be useful for studying the effects of decomposition on soil, other more specific techniques are likely to be most useful in a forensic post-mortem interval context.