The Angel's Glow: Battlefield Legend Meets Biology
June 9, 2015 10:59 AM   Subscribe

Teenage American Civil War buff Bill Martin was fascinated by a legend of soldiers at the battle of Shiloh whose wounds glowed an eerie blue-green at night and who subsequently had better recoveries, a phenomenon dubbed "the angel's glow." He knew from his microbiologist mom's work that some soil bacteria were bioluminescent, and wondered if there could be a connection. Turns out, yes there probably was!

Martin and his friend Jon Curtis did some research and decided to experiment. Photorhabdus luminescens, the bacteria that Bill’s mom studied, lives in the gut of nematode worms and has a curious symbiotic relationship with them. The parasitic nematodes burrow into insect larvae and then regurgitate P. luminescens into the host. The bacteria, which are bioluminescent and emit a blue glow, produce a cocktail of chemicals including some that kill the larvae and also antibiotics that suppress other microorganisms. This allows P. luminescens and the nematode to feed and multiply without competition. Once the insect corpse is consumed the nematode once again eats the P. luminescens which re-colonize its gut and hitch a ride on to the next insect host. Finding that next host should be easy, since it is theorized that the glow from the bacteria may attract other insects.

It turns out P. luminescens are (mostly) harmless to humans, but the chill conditions at the Shiloh battlefield may have enabled them to colonize the wounds of injured soldiers (normally human body temperature is too warm for the bacteria) and the antibiotic compounds they release might have reduced the rate of infection for soldiers who experienced these glowing wounds.

USDA Agricultural Research Service report from 2001 on the original student science project.

AAAS Science Update with audio interview clip.

An account of the phenomenon that references WWI rather than the American Civil War.

Evidently this theorized connection isn't totally new, as there are references to it in a 1998 paper, a 1988 book on bioluminescence and a 1939 academic journal (though the 1939 text doesn't quite get the mechanism right).
posted by Wretch729 (5 comments total) 39 users marked this as a favorite
Nature never seems to fail to amaze me.
posted by Samizdata at 11:19 AM on June 9, 2015

This is awesome, Wretch729.
posted by Sleeper at 11:54 AM on June 9, 2015 [1 favorite]

Another cool thing about Photorhabdus luminescens is it has a gene called makes caterpillars floppy (mcf), which encodes a toxin that causes caterpillars to go all floppy like before it kills them.
posted by bismol at 12:01 PM on June 9, 2015 [7 favorites]

That was nifty!
posted by TedW at 1:33 PM on June 9, 2015

Thanks for posting that.
posted by zzazazz at 4:09 PM on June 9, 2015

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