While we are alive, we have intimate relationships with the microbes — the microscopic bacteria, yeast, and other critters — that live on, and inside of, our bodies. We’re only just beginning to learn about the vital roles these microbiomes play, but already we’ve found they’re closely tied to aging, as well as medical conditions such as obesity, autoimmune diseases, and infections. And, unsurprisingly, they play essential roles in the death and decomposition of our body as well.
(Note: The rest of this article contains a graphic image.)
A recently published paper explored how the bacterial communities on human cadavers change over time as the body decays. Such a technique could be quite useful for dating corpses and determining post-mortem details, such as whether the corpse was moved after death, and where it might have been moved from.
A powerful aspect of this study is that genetic sequencing was used to identify the bacterial species and strains. Previous studies have primarily tried to identify these microbes by growing them in laboratories, but, according to an author of the recent paper, this approach may only reveal about 1% of the bacteria living on the corpses (due to the difficulty of growing them in a lab setting). Consequently, this new study was able to identify many novel bacterial species.
In this particular study, two cadavers were placed outdoors among trees and shrubs and allowed to “naturally” decompose. (This was done at one of only four facilities in the U.S. where cadavers can be investigated in natural settings such as this.) The decomposition stage the researchers focused on was the “bloat stage,” which is visually recognizable as the point when the corpse becomes bloated due to the buildup of gases produced by the corpse-consuming microbes. (For an engrossing read on how the natural decomposition process led to stories of vampires and zombies, check out my book Biology Bytes: Digestible Essays on Animals Both Commonplace and Bizarre.)
The researchers found that the most notable shift in bacterial populations during the bloat stage was from aerobic bacteria (bacteria that need oxygen to survive) to anaerobic bacteria (ones that don’t want to be around free oxygen). This is likely due to tissues losing oxygenated blood. But while this general trend was observed, a lot of variation was also present between the necrobiomes of the two cadavers, as well as on different parts of the same cadaver (since different areas are often at different stages of decomposition). Additional studies need to be done to characterize other general trends to improve corpse dating techniques based on the necrobiome.
We surly still have much to learn about our microbiomes, both in life and in death.
For further reading:
- Embriette R. Hyde, Daniel P. Haarmann, Aaron M. Lynne, Sibyl R. Bucheli, and Joseph F. Petrosino’s article “The Living Dead: Bacterial Community Structure of a Cadaver at the Onset and End of the Bloat Stage of Decomposition“
- ScienceDaily’s article “The Necrobiome”
- Teisha J. Rowland’s book Biology Bytes: Digestible Essays on Animals Both Commonplace and Bizarre