Utilization of microbial structure and function in investigations of criminal justice

As submitted by the proposer: Determination of the postmortem interval is a critical measure following events of homicide or un-witnessed deaths, and resolving the precise window of time and location of both the decedent and witness(es) is essential for excluding or including witnesses, and unlocking circumstances leading to death. However, there are challenges with reliability and accuracy in describing the postmortem interval (PMI). While there are recognizable changes that a body undergoes during decomposition, there are key variables that advance and retard the rate of these processes. Some significant factors include environmental conditions, body habitus, predation, external microbiota, and microbes resident to the human body, known as the microbiome. Microbially mediated mechanisms of human decomposition begin immediately after death and are a driving force for conversion of a once living organism to a resource of energy and nutrients. Little is known about postmortem microbiology in human cadavers, particularly the microbial structure of microflora residing within the human ecosystem, and their associations with decomposition stages; however, recent work suggests that these bacterial communities are surprisingly dynamic during the postmortem interval. Further, bacteria respond to stress and changing host conditions through competition, dispersal, and modulating gene expression that control bacterial structure and function. Gene expression is a carefully controlled, dynamic process, and only a fraction of genes are active at a single time and under specific conditions. An understanding of how bacterial genes, and ultimately the proteins they encode for function during host decomposition will provide a foundation for development of biochemical assays with potential for quantifying metrics such as PMI in a forensic investigation. In a first-of-its-kind effort, we seek to expand studies of the postmortem microbiome by partnering with a major, metropolitan city's medical examiner's office to sample and analyze, using next-generation sequencing and imaging technology, bacterial communities from six anatomical areas of at least 200 human cadavers to maximize demographic sampling and representation, several different manners of death, and confirmed PMIs. In another novel series of transformative controlled laboratory studies using fluorescently labeled bacteria in vertebrate models, we will describe how the microbiome of a living host changes and translocates within the body after death - linking the microbiome of a living being to the postmortem microbiome changes, which have demonstrated such promise as usable evidence in criminal investigations. Data obtained will significantly further investigations identifying specific microbial taxa or metabolic signatures for potential use in quantifiable, precise measurements of PMI used in forensic science. ca/ncf