The notorious E. coli bacteria, renowned as a source of food poisoning, has lately been undergoing something of a rehabilitation tour. Various strains of E. coli are being developed to make sustainable biofuels or convert sunlight into usable energy, and in the latest example, a team of chemists from Tufts University in Massachusetts has engineered new strains of fluorescent E. coli bacteria. These strains can grow into colorful pattens that could form coded messages, signs, or works of art, reducing the need for inks or paints based on petroleum products and toxic chemicals.
Glow-in-the-Dark E. Coli
The Tufts research, lead by chemistry professor David R. Walt, resulted in the creation of seven new strains of bacteria that display different fluorescent colors. Like any color code, the bacteria can be arranged in different sequences to represent letters, numbers, and punctuation. The tricky part is to get each strain to stay in a discrete area. The team solved that by using a microtiter, which is a slim tray that has a grid of small wells or depressions arrayed on its surface, each of which can hold a microscopic amount of bacteria.
Self-Assembling Art from Bacteria
The process of making “art” from the bacteria is fairly straightforward. After the different strains are arranged in a pattern on the microtiter, the whole array can be transferred to a membrane. The membrane is a neutral environment (the team used nitrocellulose, which movie buffs may recall as the highly flammable ingredient in old film), which preserves the bacteria without enabling them to divide, so the array can be shipped or stored if needed. When it’s ready for use, the array is transferred to a growth medium, and the colonies grow large enough to become visible.
From E. coli to Cryptography
A skilled cryptographer could easily crack a dotted color code, but since bacteria are living organisms there are a few twists that would make an E. coli code more difficult to pick apart. While still on the membrane the sequence is invisible, so the decoder would have to know where to find it and then expose it to an appropriate growth medium. Also, with some additional engineering the fluorescent properties of the bacteria can be made to lie dormant, and the message will not appear until a specified period of time passes, or until they are exposed to a certain chemical.
Antibiotics can provide another layer of encryption. An array can be made with bacteria that are immune to different antibiotics, so that exposure to one antibiotic will preserve some parts of the array but not others. With this method, more than one message can be sent in the same array.
Additional twists can be added by using strains of bacteria that reveal their fluorescence when exposed to different wavelengths of light. Future plans include engineering strains that will die off after a specified time, adding a new twist to the famous line, “This tape will self destruct in five seconds.”
Bacteria and Sustainability
E. coli is not the only bacteria marking out its place in a more sustainable future. Researchers are developing bacteria that can convert old newspapers to biofuel, produce valuable fuels and chemicals out of waste from biofuel refineries, generate electricity, and help plants suck copper and other contaminants out of soil. A living E. coli ink or paint is a long way from commercial development, but the Tufts researchers envision that in the future it could be used for bar codes, counterfeit prevention, or of course, the secret transmission of messages.
Image: Fluorescent straws by Spacepleb on flickr.com.