A recipe for scientific discovery: seaweed and Jell-O
When I was late for dinner as a boy, my mom would put the food on my plate and set it on the table until I came home to eat. I didn’t mind cold food so much, but the hot food on the plate would melt the Jell-O. Then the Jell-O would run all over the plate, and I hate lime Jell-O in peas.
Gelatin is an interesting compound. It is derived from a protein in vertebrate animals called collagen, which is found in cartilage and tendons. It is used as a thickening agent in foods, pharmaceuticals and cosmetics, but most of us know it as Jell-O. When making Jell-O we’ve learned that gelatin thickens as it cools but turns watery at room temperature or higher.
It was about 150 years ago when humans discovered bacterial diseases. An early problem with growing bacteria was that it could only be grown in liquids. That meant the bacteria were all mixed together, and it was difficult to get pure cultures of just one kind.
The German physician Robert Koch noticed some colored spots growing on the surface of some leftover potatoes. He teased some of the growth off with a needle and looked at it under a microscope. It was bacteria, of course, and they all looked alike. It struck him that maybe what he was seeing was a pure culture, and that using a potato surface could help him grow pure cultures of bacteria.
Growing bacteria on any surface kept the organisms in one place. This realization turned out to be key to isolating and growing pure cultures of bacteria and was a major breakthrough in bacteriology. However, there were other difficulties. Some bacteria liked potatoes about as much as I liked limed-peas. Who knew bacteria were such fussy eaters? So in search of a better surface area, Koch tried different gelling compounds, including gelatin.
Bacteria grew on gelatin surfaces just fine. But gelatin has to be kept chilly to have a surface, and many bacteria don’t grow well when it is cool. You wouldn’t think a single-celled creature could be so selective in its habits. (In contrast, no one pays much attention to what temperature I think my office should be.) Well, when it got warm in the lab, the gelatin would turn to soup, and it would run all over the plate, mixing up the bacteria again.
Koch had an assistant in his lab named Walter Hesse. Hesse’s wife, Angelina Fannie Hesse, also worked in the lab part-time. She watched everyone’s frustration as the gelatin melted in the hot labs. One day, over lunch, Walter asked “Lina” why her jellies and puddings stayed solid even in the summer heat. She told him about a heat-resistant gelling agent known as agar that she had learned about as a child growing up in New York.
She had learned about it from a Dutch neighbor who had emigrated to America from Java. An Asian woman taught a Dutch immigrant about agar, who taught an American girl in New York, who married a German and brought agar into medical research.
Agar is derived from seaweed. It has some unusual properties. Agar is a kind of sugar that doesn’t melt until heated above 100 degrees C, but then remains a liquid until it cools below 50 degrees C. Once it has gelled, it remains a solid until it is heated above 100 degrees C again. That means it is a solid at room temperature and is a perfect surface for growing bacteria.
Agar is found in many foods and consumer products ... maybe to keep stuff from running into the peas. You might be interested in checking out the contents of products in the grocery store for words such as agar, carrageenan (a similar seaweed product), agarose, agarbiose, D-galactose or 3,6-anhydro-L-galactopyranose.
OK, forget that last one. I can’t remember it either. (Hints: toothpastes, vitamins, ice cream, antacids, jellies, noodles, soups, sauces, candy bars.)
Gary McCallister is professor of biology at Mesa State College.