Forensic DNA Profiling of Bacterial Communities in Soil

Soil is frequently encountered as trace evidence in forensic science case-work, but because of the limitations of current analytical techniques, this evidence is rarely utilised. A technique has been developed that allows comparisons of soil samples to be made, based on molecular analysis of the bacterial communities living in the soil. This project assesses the practicality of using this technique, known as 16S rDNA T-RFLP community profiling, for forensic soil analysis, by refining the basic methodology and performing a preliminary evaluation of its reproducibility and utility. Initial difficulties associated with generating profiles from soil samples have been overcome through methodology improvement, and the technique has been found to be effective for generating simple, visual profiles that clearly demonstrate differences between soil samples. Soil bacterial community DNA profiling is likely to be a powerful yet simple forensic tool, providing the ability to routinely use soil as associative evidence. The potential for using the same technology to develop a time since death or post mortem interval (PMI) estimation tool was also investigated. This study monitored the changes in the soil bacterial community beneath decomposing human cadavers and pig carcasses and showed that community change is dynamic and progressive. These changes are caused by fluctuations in specific bacterial species populations that are able to utilise organic breakdown products released from the body over time. Release of the body’s natural microflora into the underlying soil may also contribute to an altered bacterial community. This project has demonstrated that the soil microbial community clearly changes over the course of decomposition, and potential exists for development of a PMI estimation tool based on soil bacterial community succession.