Contributed by Ariane Thomas
During my first year as a forensic anthropology graduate student, I was exposed to biomolecular topics and their applications in forensic contexts. Combined with my previous experiences at the Office of the Chief Medical Examiner in Connecticut and the Central District Major Crimes Unit, I developed the core of my Master’s thesis: an analysis of the presence of eukaryotic DNA in soil samples surrounding burials. An increased understanding in the degradation rate of DNA will have the potential to assist forensic investigators in casework or even bioarchaeologists with historic skeletal remains.
In ancient and forensic contexts, DNA proves to be an invaluable resource as a unique identifier of dietary habits, sex, ancestry, and more. The most common sources of DNA are bone, tissue, blood, and other biological material. Recently, studies have broadened their scope and began focusing on other outlets to extract DNA from, such as soils. Despite the large amount of literature of the microbial diversity of soil ecosystems, there is relatively little information on the leaching patterns of DNA as a result of taphonomic processes. The core of my research investigates the distance viable DNA from a decomposing mammal leaches outward from the initial body placement. Due to the intense genetic component of my research, this project required funds for DNA extraction, the polymerase chain reaction (PCR) portion, additional DNA cleanup protocols, and sequencing. The Collaboration Challenge Research Grant was used to obtain the necessary materials for data collection including two DNA extraction kits (one for tissue and soil extractions), PCR reagents, and sequencing costs.
As with all scientific studies, this project was not immune from challenges. During the sequencing phase of my project, I faced a complicated problem: DNA was present in the agarose gels after PCR, but Sanger sequencing did not yield any DNA. This peculiar result forced me to review the PCR protocol. Dr. Meradeth Snow suggested minor changes to the PCR protocol and when that did not produce a better result, I contacted Tamara Max of the University of Montana Genomics Core. We conducted genomic and high-sensitivity ScreenTapes on DNA extracted from pig tissue, but the results were similar to the soil samples. Tamara noticed that the Tm scores for my primers had a high degree of difference, well over the allotted amount recommended. After searching for a new set of primers with closer Tm scores, all of my soil samples contained clean traces of pig DNA. Even the samples collected 160 mm of the cage border had traces of pig DNA. These results suggest that viable DNA can be recovered from Montana soil more than 20 weeks after initial placement even during the summer months.
The surprising results of my research will be submitted to the Forensic Science International journal for publication. I believe that this study provides the foundation for numerous DNA leaching studies in different environments, various timeframes, and farther increments away from the burial. This project has sparked my interest in new topics such as identifying the varying demographics of microbial organisms that are involved in decomposition or seeking viable DNA in burial soil after the body has been removed. I hope to continue this line of forensic studies now that I have the skills and knowledge to pursue interdisciplinary research.
Crossing disciplines not only increased my knowledge in an area briefly mentioned in my anthropology and forensic classes, but allowed me to expand on my understanding of taphonomy and genetics. The Genomics Core assistance with my laboratory protocols strengthened my laboratory techniques and skills. Under the direction of both anthropologically trained and biologically trained geneticists, I developed a mixture of the two methodologies that will benefit future work in either fields.
I gratefully acknowledge the University of Montana Genomics Core, Lubrecht Experimental Forest, and the Snow Molecular Anthropology Laboratory for resources. In addition, I must express my gratitude to all at the Interdisciplinary Collaborative Network for creating such a vital source of funding for graduate students at the University of Montana. Due to the high costs of such a project, it would not have been possible without the Collaboration Challenge Research Grant. I am appreciative of this opportunity to research the forensic applications of DNA, and learn genetic analytical methods from multiple collaborators.