Standing between your dead body and its eventual star-stuff fate are a whole lot of bugs and chemicals. Bodies rot and putrefy, and this is how it should be. But, as a future corpse, you may be surprised to learn that this process is still poorly understood.
A study out this week in Science takes a deep look at the process of “microbial community assembly” as dead human and dead mouse bodies decomposed on varying substrates of soil. One intriguing result is that the microbe varieties needed for proper decomposition are nearly ubiquitous across all different types of soil, albeit in often very low concentrations. Once a corpse has been introduced, this microbial background quickly comes to life.
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The corpse, perhaps yours or mine, becomes a whole new bacteria habitat. Within this habitat (read: you) takes place a critical stage in the broader ecosystem’s process of nutrient cycling, in which organic and inorganic matter is eventually “reborn” in a living organism as a basic nutrient, like nitrogen or phosphorus. From dust to dust, as they say.
The bacteria that make all of this happen have to come from somewhere, whether it’s the soil or the body itself. Are they the same regardless of season, environment, and evolutionary history?
“Are microbial decomposer communities ubiquitous?” the study asks. “From where does the microbial decomposer community originate? How does mammalian decomposition affect the metabolic capacity of microbial communities?”
To answer these questions, the researchers took a bunch of corpses and watched them rot, basically. Some corpses were mice, which were observed in more controlled laboratory settings, while others were humans, which were observed in the great outdoors.
One of the best things about decomposition is that it happens to everyone
About that: “Outdoor experiments on human cadavers were conducted at the Sam Houston State University Southeast Texas Applied Forensic Science (STAFS) Facility, a willed-body donation facility, where human bodies were exposed to all natural elements including invertebrate and vertebrate scavengers,” the study explains. “We sampled the skin and gravesoil associated with four decomposing human subjects, two of which were placed in the winter and two in spring over 143 days and 82 days, respectively.” (Is “gravesoil” not your new favorite scientific term?)
As bodies rotted, samples from the, uh, subjects’ skin, abdominal cavities, and gravesoils were taken daily for the first month and every other day after that. The collected microbes were then genetically sequenced with the result being regular snapshots of the decomposing bodies, or the diverse taxa (bacteria, fungus, worms) calling those bodies home. Eventually, researchers were able to use all of this data to come up with solid predictions of what microbial activity might be expected at different points of decomposition, regardless of season or even soil types. Indeed, Earth is just waiting for you to drop dead.
The whole process is pretty great. Paraphrasing from the study, decomposition begins with the bacteria in your intestines, who, no longer kept in check by a living immune system and a regulated body temperature, go to town. Eventually, your body gets so bloated it bursts and one of the things that leaks out is ammonia. This changes the nitrogen concentration and pH of the gravesoil, leaving conditions that are suddenly awesome for things to grow.
Meanwhile, back in your abdomen, a grand symphony of tiny, interdependent lifeforms (again: bacteria, fungi, worms) dig in. The genetic diversity of your guts goes through the roof.
“Decomposition is a fundamental microbial function spanning terrestrial ecosystems and, while plant inputs are the dominant source of organic matter, vertebrate corpse inputs can be significant resources,” the study explains. “For example, one rain forest in Panama was estimated to receive 750 kg in mammal cadavers annually per square-kilometer.”
“While this represents less than 1% of the mass of plant litter received by another Panamanian rain forest, cadaver nutrient sources can be an order of magnitude more concentrated than plant litter,” the authors continue.
One of the best things about decomposition is that it happens to everyone (assuming it’s allowed to proceed). Even very crappy people will make a fine “disturbance habitat” for new life as the community centers of whole tiny universes.
