The Same Microbes Help Bodies Decompose No Matter Where They're Buried

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We may all become worm food in the end, but scientists haven't been sure exactly how that process happens. Now, a new study in the journal Science pinpoints how microbes from the soil go about turning cadavers into nutrients. 

Researchers led by Jessica Metcalf of the University of Colorado, Boulder and Rob Knight of the University of California, San Diego analyzed how bodies decompose by examining both dead mice buried in soil from different places (two spots in Colorado and one in Texas) and human cadavers donated to the Sam Houston State University Southeast Texas Applied Forensic Science (STAFS) Facility. The bodies in Texas were buried outside at different points in the year, and researchers checked in on them frequently—as much as every day in the first month after burial, then less frequently after that.

They found that whether the soil was from the Texas desert or the Colorado forest, the microbes that helped the mammal bodies decompose were the same—and they came from the soil, not from the body’s microbiome, as previous research had suggested. The organisms that break down bodies into soil nutrients are consistent across soil type, location, weather, and the presence of scavengers.

Specifically, they discovered an increased abundance of bacterial groups like proteobacteria and firmicutes as the body spent more time in the soil. (The latter is also associated with spoiled beer.) As the bodies decayed, they found an increase in the microbe genes related to the nitrogen cycle and the degradation of amino acids like lysine and arginine, which break down into the foul-smelling byproducts cadaverine and putrescine—two putrid compounds produced by decaying tissue. 

This research gives scientists a better idea of the soil nutrients provided by the decomposition of animal bodies, and might provide fodder for research into the unique smell of death. It also could prove useful to forensic scientists, the researchers postulate. They created a computer program that could date a mouse’s time of death using the shift in microbes sampled from its decaying body. Eventually, similar work might be able to provide more accurate timelines for crimes. 

[h/t: Science]