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Developing Reliable Methods for Microbial Fingerprinting of Soil Evidence: Collection, Contamination, Storage, and Analysis

NCJ Number
David Foran
Date Published
August 2019
12 pages
This is the Draft Summary Overview of the findings and methodologies of a series of research projects that focused on the bacterial composition of soil samples, their collection from various items, and changes in soil bacterial profiles over time, with the current summary focusing on how the storage of evidentiary and known soils influence subsequent bacterial DNA profiles and other issues pertinent to the management of soil bacteria evidence.

Among the issues addressed in the most recent research are how limited quantities of soil affect bacterial DNA profiles, how different depths of forensic soil samples influence bacterial DNA profiles, how the human microbiome (i.e.,skin) affects bacterial profiles obtained from soils on worn clothing, and how the presence of blood mixed with soil affects bacterial DNA profiles. Based on the research, this report advises that various factors must be considered when using bacterial 16S rRNA gene profiling for the identification of soil; however, other factors have little or no influence on bacterial profiles; e.g., the human skin microbiome has no measurable effect on soil profiles. In addition, although depth does influence the bacterial composition of soil samples from various habitats, the bacterial profile from a mixture of soils from differing depth is dominated by the more abundant bacteria from the shallow soils. Another research finding was that when storing known soils or soils collected from evidence, the storage temperature (room temperature to -80 C degrees) has little or no influence on subsequent DNA profiles, providing that the ex-situ soil is stored so that it does not dry out. Overall, the results from these studies confirm the value of profiling soil bacteria in forensic investigations. 6 figures