Directed Research Project
Postmortem submersion interval (PMSI) is an essential factor when recovering bodies from aquatic environments. Although several studies exist on postmortem interval (PMI) estimation of mammalian cadavers in terrestrial systems, the same is not true for the aquatic systems. Cartozzo et al. (11) developed PMSI prediction models using bacterial succession data associated with waterlogged skeletal remains. This study is a continuation of the Cartozzo et al. (11) study, but the aim of this study is to compare the bacterial DNA (16S rDNA) community found on the surface of swabs recovered from waterlogged bones to the bacterial DNA obtained from ground bone itself. If both sample types produce predominantly the same bacterial DNA diversity at the same ADD intervals, then it would be quicker and more efficient to process bone swabs than to grind the bone into a fine powder. This will also minimize precious sample consumption. Porcine skeletal remains (scapulae and ribs) were submerged in a freshwater lake in cages that were collected every 250 ADD (baseline + 20 collections). Swabs collected from three ribs and three scapulae after every 500 ADD were utilized (baseline + 10 collections, N=59 swabs). DNA extraction was performed on these swab samples using ChargeSwitch® gDNA Plant Kit. The variable region 4 (V4) of 16S rRNA gene was amplified and sequenced using the Illumina MiSeq FGx Sequencing platform. The resulting data obtained from the swab samples was analyzed and compared to the sequences obtained from the ground bone samples using mother (v 1.39.5) and R (4.0.4). For both bone types, the swab samples exhibited higher alpha diversity values compared to the bone powder samples. An analysis of molecular variance (AMOVA) showed significant differences in the bacterial community structure between swab and bone samples, supported by distinct clustering for each sample type on a non-metric multidimensional scaling (NMDS) plot using Yue & Clayton distance matrix. The differences in the bacterial community structure between the swabs and bone powder samples are attributed to several low abundance taxa. Bacterial community structure did not change significantly with time/accumulated degree day (ADD) for the swab samples. The changes in bacterial structure associated with the swab and bone powder samples could be due to the influence of the surrounding environment on the swabs.
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VCU Master of Science in Forensic Science Directed Research Projects
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Available for download on Thursday, May 12, 2022