Washington, D.C. — Pee on a spaceship seems like a problem, not a solution. But someday astronauts’ urine could become food for genetically engineered yeast. And the breaths these space travelers exhale could be used to help those yeast cells work like tiny factories. They might churn out the ingredients used to make plastics. Or they could become the raw materials for nutrient supplements that keep astronauts healthy. Each might help humans survive on a trip to Mars or beyond.
The International Space Station already recycles urine. Systems on the station remove nitrogen compounds and other chemicals. What emerges is clean water that astronauts then drink. Mark Blenner now wants to take that same nitrogen from urine and feed it to his yeast.
Blenner is a chemical engineer at Clemson University in South Carolina. He talked about how pee could become plastic at the American Chemical Society’s 2017 fall national meeting in Washington, D.C.
Yeast is a kind of single-celled fungus. One yeast species is famous for making bread rise and for helping brew beer. But there are more than a thousand other species. The yeast Blenner wants to send into space is called Yarrowia lipolytica (Yahr-OH-wee-uh LIP-oh-LIT-ih-kuh). Its cells are like little factories that make chemicals called lipids. These greasy molecules include fatty acids, oils and waxes. The yeast uses its lipids to store energy. When the yeast needs that energy later, it chops the chemicals into smaller chunks.
Scientists have tinkered with the yeast’s genes. The changes they made to its genetic code can coax these cells to make new chemicals. Humans can then use these molecules to create things they need.
A couple of years ago, Blenner’s group and a team at the University of California, Riverside did this with a tool called CRISPR. That process can snip out one bit of DNA and substitute another. It’s like cutting and pasting passages within a cell’s chemical-instruction book. The researchers wrote about that work in ACS Synthetic Biology in 2016.
Instead of their natural lipids, some engineered strains of the yeast could make ingredients that go into plastics known as PHAs. That’s short for polyhydroxyalkanoates (PAH-lee-hy-DROX-ee-AL-kuh-NO-aytz). These are already used in food packaging and some medical devices. These plastics can be used as “ink” for 3-D printers. On a space mission, those printers could use PHAs from yeast to build tools or parts to repair equipment.
Scientists have engineered other strains of the yeast to pump out omega-3 fatty acids. These are molecules people need to eat for good bone and eye health. But omega-3s don’t store well for long periods. Rather than packing pills for a long journey, astronauts could make their own supplements in space.
So far, researchers have done their experiments in the lab. Says Blenner, “The tricky part is: How do we do this in space?”
Yeast needs carbon and nitrogen to live. That’s where recycled pee comes in. Urine has a nitrogen-rich ingredient called urea (Yu-REE-uh). Some researchers use urine to make fertilizer here on Earth. And Blenner has had luck growing yeast cells with urine. “They prefer it, actually, over other common nitrogen sources,” he says. His team wrote about using urea and urine to feed yeast in a paper that will appear in the March issue of Applied Microbiology and Biotechnology.
The carbon part is trickier. People breathe out carbon dioxide (CO2). But the yeast can’t use that gas directly. Instead, Blenner suggests a two-step process. Other microbes can pull carbon dioxide out of the air. Among these are cyanobacteria (Sy-AN-oh-bak-TEER-ee-uh), also known as blue-green algae. They use CO2 to make carbon-containing food for their own energy and growth. Chemists and engineers could instead feed the algae’s food to the yeast. Blenner’s team has had some success with that on a small scale in the lab.
Countdown to launch
Farshad Darvishi knows from experience that Yarrowia can grow in urine. He is a microbiologist at the University of Maragheh in Iran. He was not involved in Blenner’s project, but he has worked with this yeast for more than 12 years. In 2009, he also used urea as a nitrogen source for the yeast.
“The idea is really fantastic to recycle urine and human waste into plastic and nutrients for a space mission,” he says. But researchers will need to solve a lot of problems to get there, he adds. For example, systems in space would have to feed carbon and nitrogen to yeast in just the right ratios. Otherwise the yeast might not have enough of some molecules to grow well and make the raw ingredients that astronauts want. The yeast would need an oxygen supply, too.
Researchers also will need to design new equipment to carry out this process in space. One challenge is the minimal gravity there. Blenner currently grows the yeast in small, open flasks of liquid in his lab. That wouldn’t work on a spaceship, Blenner says — “unless you wanted your microbial cultures everywhere.” Instead, crews would need interconnected but closed containers for the yeast and blue-green algae.
Some researchers also hope to develop strains of the yeast that would eat carbon dioxide directly, Darvishi says. If that works, space factories might not need cyanobacteria at all. However, that development is still years away.
Another hurdle will be figuring out the best way to get lipids out of the yeast. On Earth, scientists can use chemicals called solvents. That may or may not be the most efficient way in space, Blenner says. For now, he says, “We’re exploring options.”
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astronaut Someone trained to travel into space for research and exploration.
biology The study of living things. The scientists who study them are known as biologists.
carbon The chemical element having the atomic number 6. It is the physical basis of all life on Earth. Carbon exists freely as graphite and diamond. It is an important part of coal, limestone and petroleum, and is capable of self-bonding, chemically, to form an enormous number of chemically, biologically and commercially important molecules.
carbon dioxide (or CO2) A colorless, odorless gas produced by all animals when the oxygen they inhale reacts with the carbon-rich foods that they’ve eaten. Carbon dioxide also is released when organic matter burns (including fossil fuels like oil or gas). Carbon dioxide acts as a greenhouse gas, trapping heat in Earth’s atmosphere. Plants convert carbon dioxide into oxygen during photosynthesis, the process they use to make their own food.
cell The smallest structural and functional unit of an organism. Typically too small to see with the unaided eye, it consists of a watery fluid surrounded by a membrane or wall. Depending on their size, animals are made of anywhere from thousands to trillions of cells. Most organisms, such as yeasts, molds, bacteria and some algae, are composed of only one cell.
chemical A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.
chemical engineer A researcher who uses chemistry to solve problems related to the production of food, fuel, medicines and many other products.
compound (often used as a synonym for chemical) A compound is a substance formed when two or more chemical elements unite (bond) in fixed proportions. For example, water is a compound made of two hydrogen atoms bonded to one oxygen atom. Its chemical symbol is H2O.
CRISPR An abbreviation — pronounced crisper — for the term “clustered regularly interspaced short palindromic repeats.” These are pieces of RNA, an information-carrying molecule. They are copied from the genetic material of viruses that infect bacteria. When a bacterium encounters a virus that it was previously exposed to, it produces an RNA copy of the CRISPR that contains that virus’ genetic information. The RNA then guides an enzyme, called Cas9, to cut up the virus and make it harmless. Scientists are now building their own versions of CRISPR RNAs. These lab-made RNAs guide the enzyme to cut specific genes in other organisms. Scientists use them, like a genetic scissors, to edit — or alter — specific genes so that they can then study how the gene works, repair damage to broken genes, insert new genes or disable harmful ones.
culture (v. in microbiology) To grow cells outside the body or their normal environment, usually in a beaker, a laboratory dish or some big vessel. To keep the cells healthy, they must be kept at the proper temperature, given the proper nutrients and provided ample room to grow.
cyanobacteria A type of bacteria that can convert carbon dioxide into other molecules, including oxygen.
DNA (short for deoxyribonucleic acid) A long, double-stranded and spiral-shaped molecule inside most living cells that carries genetic instructions. It is built on a backbone of phosphorus, oxygen, and carbon atoms. In all living things, from plants and animals to microbes, these instructions tell cells which molecules to make.
engineer A person who uses science to solve problems. As a verb, to engineer means to design a device, material or process that will solve some problem or unmet need.
fatty acid A large molecule made of up chains of carbon and hydrogen atoms linked together. Fatty acids are chemical building blocks of fats in foods and the body.
fertilizer Nitrogen, phosphorus and other plant nutrients added to soil, water or foliage to boost crop growth or to replenish nutrients that were lost earlier as they were used by plant roots or leaves.
flask A type of container with a narrow neck. In the laboratory, sterile flasks made from glass are used for conducting chemical and biological experiments.
fungus (plural: fungi) One of a group of single- or multiple-celled organisms that reproduce via spores and feed on living or decaying organic matter. Examples include mold, yeasts and mushrooms.
gene (adj. genetic) A segment of DNA that codes, or holds instructions, for a cell’s production of a protein. Offspring inherit genes from their parents. Genes influence how an organism looks and behaves.
genetic Having to do with chromosomes, DNA and the genes contained within DNA. The field of science dealing with these biological instructions is known as genetics. People who work in this field are geneticists.
genetic engineering The direct manipulation of an organism’s genome. In this process, genes can be removed, disabled so that they no longer function, or added after being taken from other organisms. Genetic engineering can be used to create organisms that produce medicines, or crops that grow better under challenging conditions such as dry weather, hot temperatures or salty soils.
gravity The force that attracts anything with mass, or bulk, toward any other thing with mass. The more mass that something has, the greater its gravity.
International Space Station An artificial satellite that orbits Earth. Run by the United States and Russia, this station provides a research laboratory from which scientists can conduct experiments in biology, physics and astronomy — and make observations of Earth.
lipid A type of fat.
Mars The fourth planet from the sun, just one planet out from Earth. Like Earth, it has seasons and moisture. But its diameter is only about half as big as Earth’s.
microbe Short for microorganism. A living thing that is too small to see with the unaided eye, including bacteria, some fungi and many other organisms such as amoebas. Most consist of a single cell.
microbiology The study of microorganisms, principally bacteria, fungi and viruses. Scientists who study microbes and the infections they can cause or ways that they can interact with their environment are known as microbiologists.
molecule An electrically neutral group of atoms that represents the smallest possible amount of a chemical compound. Molecules can be made of single types of atoms or of different types. For example, the oxygen in the air is made of two oxygen atoms (O2), but water is made of two hydrogen atoms and one oxygen atom (H2O).
nitrogen A colorless, odorless and nonreactive gaseous element that forms about 78 percent of Earth's atmosphere. Its scientific symbol is N. Nitrogen is released in the form of nitrogen oxides as fossil fuels burn.
nutrient A vitamin, mineral, fat, carbohydrate or protein that a plant, animal or other organism requires as part of its food in order to survive.
oxygen A gas that makes up about 21 percent of Earth's atmosphere. All animals and many microorganisms need oxygen to fuel their growth (and metabolism).
plastic Any of a series of materials that are easily deformable; or synthetic materials that have been made from polymers (long strings of some building-block molecule) that tend to be lightweight, inexpensive and resistant to degradation.
ratio The relationship between two numbers or amounts. When written out, the numbers usually are separated by a colon, such as a 50:50. That would mean that for every 50 units of one thing (on the left) there would also be 50 units of another thing (represented by the number on the right).
recycle To find new uses for something — or parts of something — that might otherwise be discarded, or treated as waste.
solvent A material (usually a liquid) used to dissolve some other material into a solution.
species A group of similar organisms capable of producing offspring that can survive and reproduce.
strain (in biology) Organisms that belong to the same species that share some small but definable characteristics. For example, biologists breed certain strains of mice that may have a particular susceptibility to disease. Certain bacteria or viruses may develop one or more mutations that turn them into a strain that is immune to the ordinarily lethal effect of one or more drugs. supplement (verb) To add to something. (in nutrition) Something taken in pill or liquid form — often a vitamin or mineral — to improve the diet. For instance, it may provide more of some nutrient that is believed to benefit health.
synthetic An adjective that describes something that did not arise naturally, but was instead created by people. Many synthetic materials have been developed to stand in for natural materials, such as synthetic rubber, synthetic diamond or a synthetic hormone. Some may even have a chemical makeup and structure identical to the original.
synthetic biology A research field in which scientists work on developing custom life forms in the lab. Because they make synthetic organisms, scientists who work in this field are known as synthetic biologists.
urea A nitrogen-rich chemical that the bodies of many animals produce after breaks down proteins, amino acids (the building blocks of proteins) or ammonia. People excrete excess nitrogen from the body — as urea — in urine. But many other mammals, amphibians and fish make urea as well. Synthetic urea is often a nitrogen source of plant fertilizers. In 1828, German chemist Friedrich Wöhler for the first time created urea in the laboratory. This discovery would lead to the widespread use of synthetic fertilizers in farming.
waste Any materials that are left over from biological or other systems that have no value, so they can be disposed of as trash or recycled for some new use.
yeast One-celled fungi that can ferment carbohydrates (like sugars), producing carbon dioxide and alcohol. They also play a pivotal role in making many baked products rise.
Journal: M. Brabender et al. Urea and urine are a viable and cost-effective nitrogen source for Yarrowia lipolytica biomass and lipid accumulation. Applied Microbiology and Biotechnology. Vol. 102, March 2018, p. 2313. doi: /10.1007/s00253-018-8769-z.
Meeting: M. Blenner. Biosynthesis of materials and nutraceuticals from astronaut waste: Towards closing the loop. American Chemical Society, Fall Meeting 2017. August 23, 2017. Washington, D.C.
Journal: C.M. Schwartz et al. Synthetic RNA polymerase iii promoters facilitate high-efficiency CRISPR-Cas9-mediated genome editing in Yarrowia lipolytica. ACS Synthetic Biology. Vol. 5, April 15, 2016, p. 356. doi: 10.1021/acssynbio.5b00162.