Postmortem succession of gut microbial communities in deceased human subjects

Abstract

The human microbiome has demonstrated an importance for the health and functioning in living individuals. However, the fate of the microbiome after death is less understood. In addition to a better understanding of microbe-mediated decomposition processes, postmortem succession of human-associated microbial communities has been suggested as a possible forensic tool for estimating time since death, or postmortem interval (PMI). The objective of our study was to document postmortem changes in human gut bacterial communities. Gut microflora were repeatedly sampled from the caeca of cadavers as they decayed under natural environmental conditions. 16S rRNA gene amplicon sequencing revealed that over time, bacterial richness significantly increased (rs = 0.449) while diversity decreased (rs = − 0.701). The composition of gut bacterial communities changed in a similar manner over time towards a common decay community. OTUs belonging to Bacteroidales (Bacteroides, Parabacteroides) significantly declined while Clostridiales (Clostridium, Anaerosphaera) and the fly-associated Gammaproteobacteria Ignatzschineria and Wohlfahrtiimonas increased. Our examination of human caeca microflora in decomposing cadavers adds to the growing literature on postmortem microbial communities, which will ultimately contribute to a better understanding of decomposition processes.

An Experiment to Characterize the Decomposer Community Associated with Carcasses (Sus scrofa domesticus) on Oahu, Hawaii

“…Postmortem microbial communities, regardless of carcass species, are regularly dominated by bacteria from phyla Actinobacteria, Bacteroidetes, Firmicutes, and Proteobacteria (26)(27)(28)(29)(30)41) with other phyla such as Verrucomicrobia and Fusobacteria observed with some regularity (39,41,42). The current results complement these studies by demonstrating that bacteria from these same phyla can be cultured under aerobic and anaerobic conditions.…”

“…As observed by Chun et al (25), this habitat selected for a microbial community comprising phyla Firmicutes and Proteobacteria. These phyla are regularly associated with decomposing remains (26)(27)(28)(29)(30) and are likely reducing sulfur compounds to acquire energy (Fig. 6c).…”

“…These microbes contribute significantly to decomposition (e.g., putrefaction) and can release volatile organic compounds that attract insects and scavengers . Recent postmortem microbiology has demonstrated that bacterial phyla Actinobacteria, Bacteroidetes, Firmicutes, and Proteobacteria are regularly associated with decomposing remains regardless of carcass species, season, or soil type . However, despite the surge of interest in postmortem microbiology, few studies have investigated the microbial communities associated with insect larval masses.…”

Sex‐related differences in the thanatomicrobiome in postmortem heart samples using bacterial gene regions V1‐2 and V4

“…). Furthermore, according to DeBruyn and Hauther (), Clostridia are organisms known for their role in advancing the process of decay; therefore, their observed rise in relative abundance may be due to an increase in available nutrients and energy obtained from fermentation reactions (DeBruyn and Hauther ).…”

Manner of death and demographic effects on microbial community composition in organs of the human cadaver

“…We identified many different taxa as being associated with manner of death, including Lactobacillus , Enterobacteriaceae, Sediminibacterium, Blautia , Rhizobiales, and Clostridium. In several recent postmortem microbiome studies, the clostridia were observed to proliferate postmortem (11, 12), potentially in part due to an increase in available nutrients and energy obtained from fermentation reactions (34). Most Clostridium spp.…”