animals, microbes, technology

Dating Corpses: How Microbes Can Help

Decomposition is a fascinating area of research, if you have the stomach for it. Biologists often pursue it to help make us better forensics tools, since if we understand how a body changes as it decomposes, we can get a better idea of when a person (or other animal) died. In other words, it’s all about dating corpses. One tool biologists use is blow flies (of the family Calliphoridae), which lay their eggs and raise their larva in meat (i.e., dead animals). These winged critters’ lifecycle has been so well-studied that a corpse can be roughly dated based on what stage its flies are at, but there’s a lot of room for error, resulting in apparent times of death being days to weeks off. Clearly more tools are needed to improve accuracy. And this is where microbes come into play.

(Note: The rest of this article contains a graphic image.)

blow flies Calliphoridae
Blow flies on a decaying fish head. (Image credit: Laszlo Ilyes)

In addition to examining biochemical changes and other markers, forensics researchers are also turning to microbes to help with the dating process. In fact, just last week a study by researchers at the University of Colorado Boulder and collaborators showed that they could date (mouse) corpses to within three days of their death date by examining the microbial community that’s eating the rotting body. They identified the wide variety of microbes (archaea, microscopic eukaryotes, and bacteria) from different parts of the corpses using DNA sequencing. Changes in Rhizobiales (an order of nitrogen-fixing bacteria that live on plant roots) proved to be particularly useful for figuring out the timing.

Rhizobiales forming nodules on the roots of a young legume plant. (Image credit: Ninjatacoshell)

While we still have a lot to learn about the surprisingly complex progression of decomposition, at least we’re much better off now than we were in the past; for centuries, stories of vampires and zombies turned out to be due to misunderstandings of the natural decomposition process (which is explored in detail in one of my books, Biology Bytes: Digestible Essays on Animals Both Commonplace and Bizarre). Comprehending the abstract idea that things too small for us to see have such visible results has always been very challenging for people. But not only do they occasionally have apparent effects – the tiny, microscopic organisms actually often turn out to be more important than the bigger ones. (In just this blog we’ve already explored diatoms, brain-controlling Toxoplasma, MERS, antibiotic-resistant microbes, and malaria.) We have much to learn about our microbiomes, both in life and in death.

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