Microbial "spacesuits" help bacteria convert CO2 to useful chemicals
Bacteria have been found living in some pretty hostile environments, but they're not invincible. Researchers at the University of California, Berkeley have now developed "spacesuits" that wrap around bacteria to not only protect them from the elements, but turn them into biohybrids that capture carbon dioxide and turn it into useful chemicals.
The so-called spacesuits are made of metallic organic frameworks (MOFs). These structures have some of the highest surface areas of any material, with one gram holding the equivalent surface area of a football field. That incredible hidden space means MOFs can absorb quite a lot of molecules, and have been used in the past as industrial carbon-capture filters, "electronic noses" for detecting chemicals, and membranes that can separate drinking water and useable minerals out of seawater.
In this case, the UC Berkeley researchers used MOF meshes to protect bacteria and even feed them. The overall goal was to use these bugs as a hybrid artificial photosynthesis system, which takes in carbon dioxide and produces certain chemicals that are needed in industrial use.
They started with bacteria like Morella thermoacetica and Sporomusa ovata, two species that produce acetate (vinegar) and are anaerobic, meaning they don't breathe oxygen. In fact, oxygen is poisonous to them. To survive, they instead scavenge electrons from their environment.
To boost that process, the researchers first fed the bacteria cadmium, which causes them to decorate themselves with cadmium sulfide. This natural semiconductor efficiently absorbs light and uses it to feed electrons to the bacteria. Essentially, this is using light and carbon dioxide to produce vinegar or other chemicals.
"We picked these anaerobic bacteria because their selectivity toward one chemical product is always 100 percent," says Peidong Yang, lead researcher on the project. "In our case, we picked a bug that gives us acetate. But you could select another bug to give you methane or alcohol."
But there's a problem with this process – the chemical reaction also produces oxygen and reactive oxygen species, which can kill the bacteria. And that's where the MOF spacesuits come in.
"We are interfacing these bugs with a semiconductor that overwhelms them with electrons, so they can do more chemistry," says Yang. "But at the same time this process also generates all these reactive oxygen species, which are detrimental to the bugs. We are putting these bacteria in a shell so that if any of these oxidative species comes in, this first defense, the shell, decomposes them."
In their experiments, the team had the bacteria float in a solution alongside MOFs, which ends up coating the bugs in a shell just one nanometer thick. Importantly, these MOFs were made of zirconium, which is flexible enough to still allow the bacteria to grow and divide, with more MOFs then coating the new ones.
Once enshrouded, the bacteria were protected from oxygen in the environment, as well as that created as a by-product of the chemical reactions. The team says bacteria wrapped in MOF suits lived five times longer than naked ones, at oxygen concentrations of about 21 percent.
The team says that these biohybrid bacteria could be put to work removing carbon dioxide from power plants or the atmosphere, while also producing useful chemicals. They could even become handy little factories for creating substances on space stations or other planets.
"We are using our biohybrid to fix CO2 to make fuels, pharmaceuticals and chemicals, and also nitrogen fixation to make fertilizer," says Yang. "If Matt Damon wants to grow potatoes on Mars, he needs fertilizer."
The research was published in the journal PNAS.
Source: UC Berkeley