The microbial clock tells the time of death
The bacteria and other microbes found on a decomposing corpse can be used to estimate when death occurred.
Our bodies — especially our skin, our saliva, the lining of our mouth and our gastrointestinal tract — are home to a diverse collection of bacteria and other microorganisms called the microbiome. While the roles played by many of these microorganisms have yet to be identified, it is known that they contribute to the health and wellbeing of their host by metabolizing indigestible compounds, producing essential vitamins, and preventing the growth of harmful bacteria. They are important for nutrient and carbon cycling in the environment.
The advent of advanced sequencing techniques has made it feasible to study the composition of this microbial community, and to monitor how it changes over time or how it responds to events such as antibiotic treatment. Sequencing studies have been used to highlight the significant differences between microbial communities found in different parts of the body, and to follow the evolution of the gut microbiome from birth. Most of these studies have focused on live animals, so little is known about what happens to the microbiome after its host dies. In particular, it is not known if the changes that occur after death are similar for all individuals. Moreover, the decomposing animal supplies nutrients and carbon to the surrounding ecosystem, but its influence on the microbial community of its immediate environment is not well understood.
Now Jessica Metcalf and colleagues have used high-throughput sequencing to study the bacteria and other microorganisms (such as nematodes and fungi) in dead and decomposing mice, and also in the soil beneath them, over the course of 48 days. The changes were significant and also consistent across the corpses, with the microbial communities in the corpses influencing those in the soil, and vice versa. Metcalf and colleagues also showed that these measurements could be used to estimate the postmortem interval (the time since death) to within approximately 3 days, which suggests that the work could have applications in forensic science.
To find out more
Listen to Jessica Metcalf talk about bacteria and forensic science in episode 5 of the eLife podcast.
Read the eLife research paper on which this story is based: “A microbial clock provides an accurate estimate of the postmortem interval in a mouse model system” (October 15, 2013).
eLife is an open-access journal that publishes outstanding research in the life sciences and biomedicine.
