Spatial Variation in Bacterial DNA Profiles for Forensic Soil Comparisons

Abstract

ABSTRACTThe feasibility of using bacterial DNA profiling of soil in forensic investigations is evaluated. Terminal restriction fragment (TRF) analysis of 16S ribosomal DNA may be employed to generate DNA profiles for use to discriminate between soil samples. To assess the localisation of the profiles and strengthen any evidential value of TRF analysis, small-scale spatial variability has been examined. Soil samples were collected at intervals along 2 m horizontal transects of three different ecosystems—a field, a forest, and a dune system—and TRF profiles compared. 13% to 20% of TRFs were common to all sampling points, for all transects. The mean similarity for TRF profiles at all sampling points ranged from 49.3% for the dune system to 58.4% for the field transect. ‘Patch size’ (distance along the transect in which DNA profiles showed highest similarity) ranged from 20–80 cm for each ecosystem. This small- scale variability may cause problems if forensic ‘matching’ of soil DNA profiles is attempted, unless the precise location from which the soil sample was originally taken could be identified. The implications of these findings for forensic fingerprinting of soil samples are discussed.