Microbial Masons Cement Bricks for Lunar Habitation

Back in 1969, Neil Armstrong famously took one small step for a man and one giant leap for mankind. Following this, 11 people walked on the moon, with the last astronaut leaving his footprints on the lunar surface in 1972. Now, more than half a century later, space organizations are gearing towards resending humans to the Moon and building long-term settlements there for research purposes.¹

Aloke Kumar, a mechanical engineer and biophysics researcher at the Indian Institute of Science, has always been fascinated by space colonization research. This led him to collaborate with the Indian Space Research Organization (ISRO) on building extraterrestrial infrastructure. Kumar explained his back-to-basics process, “I asked myself a simple question: If an astronaut has to have a house on the Moon, what would it look like?”

So, Kumar set out to build “space bricks” made out of lunar soil-like material.² In this endeavor, his team turned to a bacterial species, Sporosarcina pasteurii, to develop bricks with substantial mechanical integrity. They also found that this bacterium can seal cracks in sintered bricks, highlighting a sustainable solution for building and repairing construction materials in extraterrestrial environments.³

The team had to be mindful of several things when they started this project. “A sustainable colony has to use as [many] resources as possible locally,” said Kumar. This aligns with the National Aeronautics and Space Administration’s ideology of in situ resource localization, where astronauts harness local natural resources at the destination instead of carrying supplies from Earth to reduce the cost of space missions.

Six bottles with blue caps hold several brown-colored bricks. — Kumar and his team made and collected several space bricks for testing in the lab.
Matjaž Tančič

The lunar surface is abundant in fine soil, called regolith, which can be used as raw construction material. Kumar and his team collaborated with scientists at ISRO who had developed a lunar soil simulant resembling the chemical, mineral, and mechanical properties of the Moon’s regolith.⁴ They next focused on consolidating the fine particles into structures that would have mechanical integrity.

The researchers turned to a biomineralization process called microbial induced calcite precipitation (MICP), commonly used for cementing structures. MICP involves the crystallization of calcium carbonate within soil by microorganisms. Kumar and his team used a soil bacterium S. pasteurii, which hardens sand in the presence of calcium and urea and is used to enhance the mechanical strength of concrete construction materials.⁵ The bacterium secretes urease enzyme to hydrolyze urea, triggering a series of chemical reactions resulting in carbonate ion production. Combining with a calcium source leads to calcium carbonate precipitation, which serves as both a filler and a cementing agent that enhances the mechanical properties of construction materials.

In practice, the experiment turned out to be much harder. “For a few years, we struggled even keeping this bacterium alive with the Moon sand,” recalled Kumar. Over time, the team realized that adding a biopolymer extracted from guar seeds—guar gum—made the lunar soil simulant more habitable for the bacterium.⁶

The researchers prepared a slurry containing the simulant soil, S. pasteurii, and guar gum in aluminum molds; the mixture consolidated into bricks over a few days. Moreover, these bricks had compressive strength comparable to commercially used mud bricks.²

A person wearing purple gloves holds a mold containing four grey-brown bricks. — Kumar and his team made space bricks by pouring a slurry consisting of lunar soil stimulant, guar gum, and S. pasteurii into a mold.
Matjaž Tančič

Next, Kumar said he and his team asked, "What happens if this kind of brick has a failure [on the Moon]?" The lunar environment is harsh: In addition to threats of meteorite impacts, the surface temperature can vary anywhere between 250°F (121°C) in the daytime to -208°F (-133°C) after nightfall, which can fracture the bricks. Since other researchers had previously shown that MICP can effectively repair cracks in terrestrial bricks, Kumar and his team investigated whether the MICP-based slurry could repair sintered space bricks.⁷

They subjected lunar soil simulant to a high temperature and sintered it to form synthetic space bricks.⁸ They introduced various cracks in these bricks, and poured a slurry made of regolith simulant, S. pasteurii, and guar gum. Over time, the bacterially-produced calcium carbonate helped fill the cavities in the bricks, significantly strengthening their mechanical properties.³

Will the bacterium undergo the same metabolic pathways to yield similar results in space? “That’s the million-dollar question,” said Kumar. “We always envision that, if aliens come to earth, how will they survive?” But when these microbes go to the Moon, they become aliens there, raising questions about their adaption and survival.

Kumar hopes to have some answers soon: The team has recently started conducting experiments in space-like conditions using vacuum chambers and microgravity simulators. They are also in the process of brainstorming a payload design with lab member Shubhanshu Shukla, an astronaut designate for India’s Gaganyaan Mission, for carrying the bacterium to space to test its behavior in microgravity.

But for now, this project has made Kumar appreciate Earth a bit more. “When I started learning more about the Moon and Mars, I started understanding how Earth was different,” he said. “It made me much more informed about how our life is and to be grateful for the life-sustaining conditions [on Earth].”