Glowing Bacteria: Bioluminescence

I'm a physicist for the US Department of Energy and I teach at a state university. I'm used to people dropping by with questions about stars and black holes, armchair scientists who are struggling to understand quantum mechanics, and the occasional whack who wants me to look over his proof that the laws of thermodynamics are wrong. It was a typical Friday and I was nearly done for the day when one of my former students arrived, with an "Urgent physics question!" Her shortness of breath made it clear that she had ran to my office.

I asked, "What's going on?"
"I'm worried I'm gonna die!" she quickly replied.
A little startled, I asked, "Why what's wrong?"
"Today when I got home from class, I opened up my refrigerator and the light bulb had burnt out-I could see that my crab salad was....was....glowing!"
"Glowing....Really?!" I exclaimed with excitement.
Approaching tears she said, "I ate some of that crab salad for dinner last night! It must be radioactive! Oh God, my hair is going to fall out and I'm going to die!"
I laughed out loud and said, "Sarah, I think you're gonna be fine!"

What Sarah had encountered was a common type of bacteria which, believe it or not, glows in the dark! This type of bacteria is actually quite common in fresh sea food, but most of us usually aren't looking at our food in the dark and usually there is not enough of the bacteria on the food for us to see the glow even if we were. In Sarah's case, the electricity had been knocked out in her apartment by a storm. Since the refrigerator had not been running all day, the warmer temperature likely allowed the bacteria to grow faster than normal.

She had brought some of the salad in to show me. After a quick Geiger counter measurement to prove to her that there was no radioactivity, we shut off the lights. After a half minute or so of letting my eyes adjust to the darkness, I could clearly see a green glow emanating from her salad. I had heard of this before, but I had never seen it with my own eyes. From that moment on, I have been fascinated by bioluminescense-glowing plants, animals and bacteria.

Almost everyone has seen bioluminescence in one form or another. Indeed the firefly is the most familiar example, but there are a plethora of light emitting organisms out there: from bacteria, to fish, to bugs, to mushrooms. After my immediate captivation, I set out to see as much bioluminescence as possible. I started out by looking for various glowing mushrooms. There are several species in North America. The most common in the US is the Jack-O-Lantern mushroom, Omphalotus illudens. This proved to be quite a hunt, but I eventually found some.

What I really wanted was something I could show people in person. Although I could photograph the Jack-O-Lantern mushroom, most people weren't going to be willing to hike into the forest on a moonless night to see a glowing mushroom. I experimented with cultivating the mushroom with no success. However, I did find a very simple way to grow bioluminescent bacteria after much trial and error. In fact you can grow it in your own home with very little work and it's a wonderful science project for kids.

It turns out all you have to do is get some fresh shrimp and let it sit out for while. Now it is important that the shrimp actually be fresh! If it is kept on ice, it will likely have some strains of glowing bacteria on it. Frozen shrimp doesn't seem to be nearly as reliable as fresh shrimp.

Take several fresh shrimp and place them in a bowl. Now mix one tablespoon of salt into a liter bottle of water and shake it up. Pour the water into the bowl until the shrimp are half submerged. Place the bowl in a dark closet or bathroom and wait. Every couple hours go into the darkened room and give your eyes one minute to adjust. Between two to eight hours after the shrimp have been sitting they will likely begin to develop glowing spots called colonies. If you are lucky an entire shrimp will be glowing!

The glowing bacteria on shrimp and crab is likely Vibrionaceae Photobacterium, which is actually in the same family as vibrio choloerae-the bacteria which causes the illness cholera. However, these glowing strains of bacteria are not pathogenic and therefore cannot make you sick. These bacteria glow because they contain a series of genes collectively known as the Lux operon. This series of genes has been successfully tranfered into other bacteria by scientists. Some scientists have even suggested it would be possible to transfer the gene into other animals to create novelty pets like glowing mice and rabbits. This idea isn't so far fetched since there are already glowing bugs, worms and fish. In fact 90% of all deep sea fish have light emitting organs.

Bioluminescent bacteria don't only grow on shrimp and crab. They can grow on many different types of marine life, or they can exist by themselves. In Jule's Verne's Twenty Thousand Leagues Under the Sea, the Nautilus passes through a 40 mile region of the sea which is glowing blue and is explained as an uncountable number of tiny luminous worms floating in the water. This was not a mere fiction created for the book. There are indeed huge regions of the sea filled with the bacteria Vibrio harveyi which can cause miles and miles of the ocean to glow. In 2005 a scientist named Steven Miller, discovered that a U.S. defense satellite had unknowingly photographed a 6,000 square mile region of such glowing sea water!