"Space suits" protect microbes destined to live in space

Chemists at the University of California at Berkeley have developed protective suits to extend the life of the bacteria in a unique system that combines live bacteria with light-absorbing semiconductors to capture the dioxide of carbon and convert it into chemicals that can be used by industry or possibly in the colonies of space.

The system mimics photosynthesis in plants. However, while plants capture carbon dioxide and convert it to the carbohydrates we eat often, the hybrid system captures CO2 and light to produce various carbon compounds, depending on the type of bacteria.

The bacteria used in the experiment are anaerobic, which means that they are suitable for living in oxygen-free environments. The combination – a mosaic of mesh-shaped pieces called Metallic / Organic Frame (MOF) – is impermeable to oxygen and reactive oxygen molecules, such as peroxide, which shorten their lifespan.

The hybrid system could be a winning solution for the industry and the environment: it can capture the carbon dioxide emitted by power plants and turn it into useful products. It also provides a biological means of producing the necessary chemicals in artificial environments such as spaceships and habitats on other planets.

"We use our biohybrid to fix CO2 in the manufacture of fuels, pharmaceuticals and chemicals, as well as that of nitrogen for the manufacture of fertilizers," said Peidong Yang, Chairholder SK and Angela Chan in Energy Department of Chemistry, University of Berkeley. "If Matt Damon wants to grow potatoes on Mars, he needs fertilizer."

Yang, a faculty researcher at the Lawrence Berkeley National Laboratory and co-director of the Kavli Energy Nanoscience Institute, was referring to the actor who played the protagonist in the film The Martian. Damon's character was abandoned on Mars and had to use his own garbage as fertilizer to grow potatoes for food.

The research, funded by NASA through the Center for the Use of Biological Engineering in Space at the University of Berkeley, will be on-line this week before being published in the journal. Proceedings of the National Academy of Sciences.

A hybrid of bacteria and semiconductors

Yang and his colleagues have been developing the hybrid bacterial system over the last five years on the basis of their work on light-absorbing semiconductors such as nanowires: silicon wires of a few hundred nanometers, where a nanometer is a billionth of a meter. Networks of nanowires can be used to capture light and generate electricity, promising cheap solar cells.

The hybrid system takes advantage of the efficient capture of light by semiconductors to supply anaerobic bacteria with electrons, which normally capture electrons from their environment. The goal is to increase carbon capture by bacteria to produce useful carbon compounds.

"We are interfacing these insects with a semiconductor that submerges them with electrons so that they can do more chemistry," Yang said. "But at the same time, this process also generates all these reactive oxygen species, which harm the insects.We put these bacteria in a shell so that if one of these oxidant species enters, this first defense, the shell, decomposes them. "

The combination is made of an MOF mesh that envelops the bacteria and covers them in plates. By wearing these MOF suits, bacteria live five times longer at normal oxygen levels – 21% by volume – than without combinations and often longer than in their natural environment, Yang said. Their normal lifespan varies from a few weeks to several months, after which they can be emptied from the system and replaced by a new batch.

In this experiment, researchers used a bacterium called Morella thermoacetica, which produces acetate (acetic acid or vinegar), a common precursor of the chemical industry. Another bacterium in their test, Sporomusa ovata, also produces acetate.

"We selected these anaerobic bacteria because their selectivity to a chemical is always 100%," he said. "In our case, we chose a bug that gives us acetate, but you can choose another one to give you methane or alcohol."

In fact, bacteria that ferment alcohol in beer and wine and turn milk into cheese and yogurt are all anaerobic.

While his early experiments with the hybrid system associated a bacterium with a Silicon nanowire silk, Yang discovered that in 2016, feeding the cadmium bacteria prompted them to decorate with a natural semiconductor, cadmium sulphide. , which effectively absorbs light and feeds the electrons of the bacteria. .

In the current experiment, the researchers took bacteria decorated with cadmium sulfide and wrapped them in a flexible layer of MOF of a thickness of one nanometer. While a rigid MOF interfered with the normal growth and division process of the bacterium, a zirconium-based MOF patch was found to be flexible enough to allow the bacteria to swell and divide as She was still wearing MOF, after which a new MOF in the solution dressed them.

"You can think of the MOF 2D as a graphene sheet: a thick coat covering the bacteria," said co-author Omar Yaghi, MOF pioneer and chairman of the James and Neeltje Tretter department. of chemistry. "The MOF 2D floats in solution with the bacteria and, as the bacteria replicate, they are further overlaid with the 2D MOF layer to protect the bacteria from oxygen."

Yang and his colleagues are also working to improve the efficiency of the hybrid system in terms of light capture, electron transfer and specific compound production. They plan to combine these optimized capabilities with the new metabolic pathways of these bacteria to produce ever more complex molecules.

"Once you have repaired or activated CO2, and this is the hardest part, you can use many existing chemical and biological approaches to turn them into fuels, pharmaceuticals and basic chemicals," he said. he declared.

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More information:
Zhe Ji el al., "Cytoprotective organometallic structures of anaerobic bacteria" PNAS (2018). www.pnas.org/cgi/doi/10.1073/pnas.1808829115