A comparative in situ decomposition study using still born piglets and leaf litter from a deciduous forest

Abstract

A cadaver and dead plant organic matter, or litter, are rich energy sources that undergo a complex decomposition process, which impact the surrounding environmental microbiota. Advances in molecular microbiology techniques, with study of the 16S RNA genes, in particular, have highlighted the application of forensic ecogenomics in addressing key knowledge gaps. To investigate subsurface microbiome shifts as a novel tool to establish "postmortem microbial clock" and augment postmortem interval (PMI) and time-since-burial estimations, an in situ study with triplicate underground burials of piglets as human taphonomic proxies and Quercus robur leaf litter was monitored for 270 days. Changes in microbial community structure and composition were related directly to changes in seasonal temperature, with microbial shifts more pronounced during the summer. For example, Methylococcaceae could be used as seasonal bacterial indicators, from winter to summer, in establishing postmortem microbial clock for this site. Furthermore, Methylophilaceae (Methylophilales order) and Anaerolineaceae would differentiate for the piglet and leaf litter soils, respectively, 180 days after internment.

A Combined Application of Molecular Microbial Ecology and Elemental Analyses Can Advance the Understanding of Decomposition Dynamics

“…53.762551 • N; Long. 1.244004 • W) was a woodland characterised by tree clusters of predominately oak (Quercus robur) and as loamy soil composed of clay (22%), silt (32%) and sand (46%) (Olakanye et al, 2017). It was used for forestry agriculture and not a human taphonomic facility.…”

“…To minimise scavenging activity by vertebrates, each piglet was placed in a mesh wire cage prior to burial. All nine graves were monitored at monthly intervals for the first 12 months (December 2014-December 2015Olakanye et al, 2017) then up to 24 months (January 2016-December 2016; current report) for soil temperature, pH, and microbial (bacterial and fungal) communities. Soil core samples were collected at 20-60 cm deep from all four sides of each pit using a stainlesssteel soil corer (Eijkelkamp, Netherlands), which was cleaned after each sampling with water and 99.9% (v/v) ethanol (Thermo Fisher Scientific, Loughbrough, UK).…”

“…Furthermore, Cobaugh et al (2015) reported the persistence of human-associated microbial species in soil, which are very distinct and scarce in nature thus making them possible biomarkers of human decomposition. Ultimately, microbial communities associated with gravesoil have the potential to be used as a tool to estimate time since death and locate clandestine burials (Metcalf et al, 2013(Metcalf et al, , 2016Finley et al, 2015a;Olakanye et al, 2015Olakanye et al, , 2017.…”

“…Denaturing gradient gel electrophoresis (DGGE) is an economical and reliable method used in many laboratories around the world, with the generated data analysed further by calculating appropriate ecological indices for richness, diversity and evenness. To date, most published research on characterisation of soil microbial communities for forensic applications have used classic diversity metrics such as Shannon-Wiener, Simpson index of concentration or those built within software/pipeline packages (Can et al, 2014;Olakanye et al, 2017;Olakanye and Ralebitso-Senior, 2018;Procopio et al, 2019). However, these metrics have known shortcomings and generate results that are not easy to interpret.…”

Thanatomicrobiome composition profiling as a tool for forensic investigation

“…Therefore, studies on epinecroticmicrobiome usually focus on specific classes of environmental conditions. Presently, epinecroticmicrobiome has been investigated under conditions such as submersion in water [ 62 ] and placement in forests [ 63 ]. A consistent finding of these studies is that the environmental factors, such as seasons, play a vital part on the epinecroticmicrobiome [ 12 , 64 , 65 ].…”