Life After Death: Thanatomicrobiome Sex Differences

Graduate #23
Discipline: Biological Sciences
Subcategory: Genetics

Zahra Campbell - Alabama State University
Co-Author(s): Natalie Lorenҫo and Gulnaz Javan, Alabama State University, Montgomery, AL

The Human Microbiome Project demonstrated that Homo sapiens and its related microbes have coevolved to produce what is called a second genome, or metagenome. Upon death, this metagenome is converted to the thanatomicrobiome, or ‘microbiome of death,’ and is the diverse assortment of microorganisms involved in human decomposition. Accurate determination of the time of death, or postmortem interval, is important in suspicious or unnatural deaths, particularly in criminal cases. The postmortem interval provides critical information for crime scene reconstruction and in some cases can define the difference between courtroom innocence or guilt. Conventional methods of determining postmortem interval include rate (e.g., algor, livor, and rigor mortis) and concurrence methods (e.g., gastric emptying). These methods often do not provide definitive answers, which consequently lead forensic investigators to subjective conclusions. We hypothesized that as a human body decays, time-dependent changes in the thanatomicrobiome within internal organs are also predictive of the time of death. To assess this hypothesis, we did a cross-sectional study by sampling 28 human corpses with postmortem intervals between 3.5-240 hours. The samples were obtained by swabbing tissues from 1-6 internal body sites (blood, brain, buccal cavity, heart, liver, and spleen) of cadavers. We extracted DNA and amplified the V4 region of the 16S rRNA genes. Through 16S rRNA gene amplicon-based sequencing and bioinformatic analysis, the results demonstrated that thanatomicrobiome communities of sex-specific organs correlated to the time of death. Females had a high relative abundance of Pseudomonas and Clostridiales, whereas males had Clostridium, Clostridiales, and Streptococcus in high abundance with the lapse of time. Significant differences (p < 0.05) were observed in gender and PMI for both unweighted and weighted UniFrac ADONIS tests. To date, relatively few studies have investigated the microbiome of dead bodies in a forensic context. These results suggest that the thanatomicrobiome could be useful to criminal investigators and forensic biologists as a new source of data for identifying gender and time of death. Future studies would include defining the thanatomicrobiome in various body sites (i.e., muscle, lymph nodes, and pancreas) and during different postmortem periods in the life after death. References: Can, I., Javan, G.T., Pozhitkov, A.E., Noble, P.A. 2014. Distinctive thanatomicrobiome signatures found in the blood and internal organs of humans. Journal of Microbiological Methods.106:1-7.

Not Submitted

Funder Acknowledgement(s): This study was supported by a grant from NSF/HRD 1401075 awarded to Gulnaz Javan, Assistant Professor of Forensic Science, Alabama University, Montgomery, AL 36104.

Faculty Advisor: Gulnaz Javan, gjavan@alasu.edu