Study On Predicting Burial Time Of Rat Corpse By Microbial Community Succession

Objective:Postmortem interval estimation is the focus and hotpot in forensic science research.There is no doubt that microbial community plays an important role in the process of corpse decay.Previous studies have demonstrated microbial community succession during the decomposition of cadavers could be used to estimate PMI.However,most existing studies have looked at bodies exposed to the air.In fact,in forensic investigations,burial cadavers are very common.In this study,we used high-throughput sequencing technology to detect the microbial community during the decomposition stage of buried rat cadavers.The microbial community of gravesoil samples,rectum samples and skin samples were compared to explore the succession rules of the buried rat cadavers,and a random forest model to predicting PMI was constructed using machine learning algorithm.Methods:In this experiment,we collected samples of burial SD rats at different time points.Total DNA were extracted after the pre-processing of gravesoil,rectum and skin samples.Sequencing libraries,prepared by amplifying the 16S r RNA gene region V3-V4,sequenced with the Illumina Miseq FGX platform.High-throughput sequencing reads were merged,quality filtered and clustered by using Cutadapt,QIIME,VSEARCH,USEARCH and UCHIME.Taxonomic assignment was annotated by matching the Silva(v132)database.Diversity analysis,PCo A analysis,1-Bray-Curtis distance and PERMANOVA analyses were conducted in the R software platform.We established a random forest regression model for predicting PMI based on the biomarker sets which generated by10-fold cross-validation.Results:It was found that there were significant differences in microbial community in different decomposition stages.Alpha diversity in the late stage was lower than that in the early stage.There was a significant linear relationship between the similarity of microbial community and PMI.The R~2 of the random forest regression model of gravesoil,rectum and skin samples were 86.83%,84.55%and 81.67%,and the mean absolute errors were1.82,2.06 and 2.13 days,respectively.Conclusion:The results showed that the microbial diversity decreased over the course of decomposition,and the microbial community composition of gravesoil,rectum and skin samples became more similar during the later stages of decomposition.After further studies using human cadaver samples,the microbial community succession can be used to predict the PMI of buried corpses,which is expected to be an effective investigative tool for predicting PMI in forensic cases.