The Bacteria That Might Just Be the Future of Materials Science

Sci-fi, as a super-generalized set of ideas, likes to view the encroaching future-world as a metallic, post-biology realm where robots and computer-brains populate the day to day, and even food is consumed as inert doses of pure nutrition. There is no disease unless it’s the disease, the one that knocks civilization loose. This world goes whoosh instead of squish, screek instead of moan. Biology becomes a thing of the past, and the tissues of the new world become cold and dead; membranes and mucous are no longer.

But that’s not right. If you’ve been keeping up, you’ll have noticed that as much as biology and technology apparently split, they so often find themselves reconnecting somewhere else. One such somewhere else is the realm of materials science/materials engineering. The thing is that biology, over the course of 3.7 billion years, has gotten quite good at materials science itself, and you’ll find discoveries like, say, wood being a great bacterial filter, happening on a regular basis. But that’s just the start.

Unveiled in a study today, MIT scientists have crossed over to an entirely new level of bioengineering, coaxing bacterial cells to create biofilms that incorporate non-living material like gold nanoparticles and quantum dots. The result are tissues that can do way cool biological things like “respond to their environment, produce complex biological molecules, and span multiple length scales” while also doing handy stuff like conducting electricity or emitting light, according to a press release from the institute.

Potential applications include solar cells, self-healing materials, and embedded tissues that might be able to diagnose medical conditions in vivo. "Our idea is to put the living and the nonliving worlds together to make hybrid materials that have living cells in them and are functional," says Timothy Lu, senior author of the new study. "It's an interesting way of thinking about materials synthesis, which is very different from what people do now, which is usually a top-down approach."

The particular bacteria used in the research was good old E. coli, selected because it produces what are known as "curli fibers," a certain variety of protein that allows the bacteria to attach itself to surfaces. These fibers are made from repeating chains of subunits called CsgA. These subunits can be modified by adding protein fragments called peptides, and it’s these fragments that are able to capture non-biological materials like gold nanoparticles and incorporate them into the bacteria’s biofilm.

By tweaking the bacterium to produce different sorts of curli fibers, the researchers were able to make gold nanowire, biofilm that can conduct electricity, and quantum dots, nanocrystals with quantum mechanical properties and boasting a wide range of potential applications, from quantum computing to lasers to “tagging” cancer cells for removal.

The MIT team achieved their new sort of biomaterial essentially by creating on and off switches for aspects of the bacteria’s biofilm production. Specifically, they removed the cells’ ability to create the curli fibers on their own, instead requiring the presence of an additional molecule, called AHL, only supplied by the researchers. The bacteria cells were then engineered again to only produce a specific sort of CsgA, made from the amino acid histidine, and only in the presence of another researcher-provided molecule, aTC. The combined result of the two engineering feats is the ability to vary the chemical composition of the biofilms by varying the levels of AHL and aTC relative to each other. As the composition of the film changes, so too does its ability/”willingness” to utilize particular non-biological materials.

What’s more, the team created yet another class of bacterial cells that are able to dictate to other cells what to do. Lu notes that what’s actually occurring really isn’t all that strange in the natural world. "It's a really simple system but what happens over time is you get curli that's increasingly labeled by gold particles. It shows that indeed you can make cells that talk to each other and they can change the composition of the material over time," he says. "Ultimately, we hope to emulate how natural systems, like bone, form. No one tells bone what to do, but it generates a material in response to environmental signals."

The applications for this sort of biotechnology are nearly endless. Other possibilities include building biological “lattices” on which to grow new replacement tissue for human bodies, or creating biofilms that catalyze the breakdown of waste material into biofuel.