Bennett, Nicola Alicia; (2024) The Invisible Trail: The Application of The Microbiome in Forensic Investigations. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Soil, a complex and dynamic substrate, plays a crucial role in forensic investigations due to its ubiquitous nature and ability to transfer trace evidence. The distinct physical, chemical, and biological properties of soil vary significantly with location and depth, offering valuable clues for crime reconstruction. While traditional soil analysis methods have been employed in forensic science, soil microbiome analysis presents a novel and complementary approach. This study explores the potential of utilising a 16S rRNA amplicon sequencing to characterise the soil microbiome, offering a digital signature for distinguishing soil samples and aiding in criminal investigations. The findings show that microbial communities differ significantly between surface and subsurface soils, indicating depth as a strong discriminating factor within a single site. Moreover, variations in microbial profiles allow for inferences to be made regarding the origin of soil samples, distinguishing between surficial soils which can be transferred onto footwear from walking, with soils from depth at a grave site. Across multiple sites, location emerges as a stronger differentiating factor than depth, enabling discrimination between samples even within close proximity (less than 1km). Notably, the microbiome proves valuable in distinguishing soils of the same or differing classifications. DNA concentration analysis complements microbiome profiling in determining soil depth. Informative microbial profiles can be generated from nanogram DNA concentrations, highlighting the sensitivity of the method. However, these methods are susceptible to sequencing bias and careful consideration should given to experimental design, sample collection and analysis pipeline. From the findings from the studies undertaken in this thesis it was possible to conclude that soil microbial communities vary with depth and distance; DNA concentration aids in determining soil depth; microbial profiles can be obtained from minimal DNA amounts; close-proximity samples can be differentiated; and each soil context warrants independent assessment. Overall, this research demonstrates the promising potential of soil microbiome analysis in forensic investigations, offering a valuable tool for discriminating soil samples based on depth and location.

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