The living dead: microscopic bacteria that bloom after we die unlock surprising mysteries

Peter Andrey Smith in The New York Times:

AliveNo problem in forensic science has been investigated more, and understood less, than the post-mortem interval. Medical investigators calculate the interval between death and the discovery of a body using three cardinal measurements: temperature (algor mortis), stiffness (rigor mortis) and the settling of blood (livor mortis). These factors vary depending on a person’s distribution of visceral fat, as well as their clothing, the ambient air temperature and other factors. After two days or so, though, these observations are no longer trustworthy. Schmidt keeps a copy of a statistical opus on post-mortem intervals, in which Claus Henssge and his co-authors warn against extrapolating much beyond 48 hours, but he takes an even more pessimistic view. “Post-mortem interval is one of the most pseudoscientific bits of information out there that, and I hate to use this, will never die.”

…Biologists now suspect that opportunistic micro-organisms that feed on corpses persist in trace quantities everywhere on earth. But when a person dies, the body begins to digest itself, and these mysterious organisms rapidly emerge and assemble on decomposing mammal flesh. (The microbiologist Jack Gilbert compares them to shore-bound pirates, lying in wait for the next shipwreck.) This hypothesis draws largely from a detailed study led by Jessica Metcalf, a biologist at the University of Colorado, Boulder, who late last year confirmed that communities of the same bacteria, fungi and other eukaryotes bloomed at regular intervals after death, like a microbial clock. In dead mice and in donated human remains, under varying soil conditions and across a range of temperature fluctuations, the model predicted time of death accurately across experiments.

More here.