Testate amoeba CSI

Now here is something you don’t see everyday. In fact, I am pretty sure this has never been done before.  Ildiko Szelecz and colleagues set out to answer a question that very few of you must have already pondered: could testate amoebae be used in forensic studies?

This should in fact be a very ordinary question if you know something about soil biology and protists. A dead body is a huge influx of carbon and nutrients  into the soil that it is sitting atop.  The bacterial communities will basically go wild, and all of that must influence very heavily the community of eukaryotic microorganisms that used to inhabit there.  Interestingly enough, it appears that the idea of checking out what happens to testate amoebae communities has never popped into anyone’s head before.  Testate amoebae are abundant, somewhat easily recognizable micro-eukaryotes, which despite a few taxonomic issues are quite useful as indicators of environmental conditions.  Well, I think we have to thank Miss Szelecz for kindly looking into this gory issue!

Basically, the authors hung pig cadavers of approximately 20 kilos each in a nicely setup experiment.  For each pig replicate, there were two controls – a similar sized are with nothing in it, and an area where they added a plastic bag filled with 20 kg of soil to mimic possible micro-climatic effects that do not come form decomposition itself.  They then sampled soil from beneath the cadavers at regular intervals and counted testate amoebae – what could be more fun?

pig

What happens then is truly incredible.  At first, the testate amoebae die.  The changes introduced in soil chemistry are simply not tolerable to the amoebae and by the 22nd, all amoebae under the dead body are also dead.  The two controls behaved different from each other, presumably because microclimatic conditions (evaporation, etc) are quite different under a plastic bag filled with litter.

Screen Shot 2014-03-12 at 4.54.55 PMIn the image above straight from the paper, the plain line indicates live amoebae, the short-dashed line indicates encysted amoebae, and the long-dashed line indicates dead amoebae.

After the massive amoeba genocide caused by the dead pig body, it is apparently very difficult to recolonize and rebuild the original community.  Even after almost one year, the effects of the cadaver were still noticeable in the composition of the testate amoeba community.

The authors conclude that testate amoebae may actually be good forensic tools to estimate post-mortem intervals.  I’ve heard a bigger experiment exploring distinct types of habitats is in the works.  Perhaps the authors shouldn’t be surprised if they receive a phone call from the producers of CSI or another forensic show where they are looking for some kind of new forensic evidence…

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