Microbial populations and their potential in forensic investigations

Technological advancements have increased the importance of scientific evidence in criminal investigations. The use of DNA in biological traces is a well-known example of this and various life forms can provide valuable information in forensic investigations. Microorganisms are one of the most ubiquitous life forms on earth, live in almost any habitat and often coexist in large and diverse populations, which composition is defined by the habitat. This diversity creates potential for their use in a variety of criminal cases.
This thesis explores the potential of some forensically relevant microbial populations in establishing links between item(s) and crime scene(s)/donor and in cell type identification. Bacterial terminal restriction fragment length polymorphism (t-RFLP), next generation sequencing and microarray analysis were used to characterise the microbial populations in soil and in samples from forensically relevant body sites or excrements. The chapters cover the development and validation of a t-RFLP and microarray methods to characterise and compare the populations in soil and in faeces, respectively, to determine a possible common origin of questioned samples. Decision models to evaluate the similarity between the resulting profiles were developed based on pairwise comparisons. For cell type identification microarray profiles of human-associated microbial populations were generated and clustering and classification models were constructed for data analysis. In addition to the development of these methods, three criminal cases are described illustrating the high potential of microbial population analysis in forensic investigations.