Bacterial profiling of soil using genus-specific markers and multidimensional scaling

Area of Science:

• Forensic science
• Microbiology
• Soil science

Background:

• Forensic soil identification using microbial DNA fingerprinting has yielded inconsistent results.
• Previous studies often overlooked temporal variations and local heterogeneity in soil microbial communities.

Purpose of the Study:

• To assess the effectiveness of microbial DNA fingerprinting for forensic soil identification.
• To investigate the impact of temporal variability and local heterogeneity on identification accuracy.
• To specifically examine the nitrogen-fixing bacteria, rhizobia.

Main Methods:

• Soil samples were collected monthly from five distinct habitats over one year.
• Quarterly samples were taken from cardinal directions around a central collection site.
• Terminal Restriction Fragment Length Polymorphism (TTRFLP) analysis of the rhizobial recA gene was employed.
• Multidimensional scaling (MDS) and pairwise comparisons were used for data analysis.
• "Questioned" soil samples were introduced to test grouping accuracy.

Main Results:

• Simultaneous comparison of all habitats differentiated only two soils over the year.
• Pairwise comparisons successfully differentiated four out of five soil habitats.
• Inclusion of "questioned" samples resulted in correct grouping in 40-70% of cases, varying by restriction enzyme.
• Anthropogenic soil manipulation significantly reduced identification accuracy.

Conclusions:

• Microbial DNA fingerprinting, specifically analyzing rhizobial recA gene TTRFLP, shows promise for forensic soil identification.
• Temporal and spatial variability in soil microbial communities present challenges to accurate identification.
• The technique's efficacy is diminished in soils subjected to significant human disturbance.