Gravesoil Microbial Community Structure During Carcass Decomposition.

Estimating postmortem interval (PMI) is important to every death investigation.  It allows us to accept or reject alibis as well as identify victims. At present forensic entomology is arguably the most reliable means to accurately estimate PMI at outdoor death scenes. However, active blowfly larvae, which are critical to insect based estimates of PMI, can leave a body as soon as ten days postmortem. In these cases, forensic science is ill equipped to estimate PMI accurately. A controlled laboratory experiment was conducted to determine if soil microbial ecology can be used to estimate PMI. To evaluate this we constructed incubation units comprised of petri dishes filled with 360 g of washed sea sand inoculated with 40 g of Pawnee clay loam soil. Incubation units were calibrated to a water holding capacity of 55% and left to equilibrate in plastic chambers for seven days after which a mouse carcass was placed on its left side on the sand within 30 minutes of death. Nylon mesh was used to cover the plastic container to prevent insect colonization. The temperature was kept at approximately 20¢ªC and the water content of the sand was maintained at 55%. Carcass decomposition was monitored every day for 35 days using a decomposition scoring system. In addition, carcass mass loss was measured at 8, 14, 21, 28 and 35 days postmortem. A destructive harvest design was used to avoid the influence of carcass disturbance on the rate of decomposition. Following carcass harvest, sand was collected and analyzed for lipid phosphorus, fatty acids, pH, total nitrogen, and total carbon. The experiment was replicated four times and controls (sand with no carcass) were used. The potential of fatty acids to characterize gravesoil microbial community will be discussed with the ultimate aim of estimating PMI.