Abstract:
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.
