Toxic chemical in Martian soil leads to stronger brick-building bacteria

Researchers at the Indian Institute of Science (IISc) have investigated how bacteria that can mould Martian soil into brick-like structures fare in the presence of perchlorate, a toxic chlorine-containing chemical.

In a study published in PLOS One, whose authors include Indian astronaut Group Captain Shubhanshu Shukla, the authors found that although perchlorate slows bacterial growth, it also leads to the formation of stronger bricks.

According to IISc, bacteria that thrive on Earth may not make it in the alien lands of Mars, and a potential deterrent is perchlorate, which has been discovered in Martian soil during various space missions.

Impact on earth organism

“Mars is an alien environment. What is going to be the effect of this new alien environment on Earth organisms is a very, very important scientific question that we have to answer,” said Aloke Kumar, associate professor in the Department of Mechanical Engineering and corresponding author of the study.

In previous studies, the researchers used the soil bacterium Sporosarcina pasteurii to build space bricks from lunar or Martian soil that can potentially be used to set up extraterrestrial habitats.

When added to synthetic Martian or lunar soil along with urea and calcium, the bacterium produces calcium carbonate crystals (precipitates), which help glue the soil particles together into bricks, in a process called biocementation. The process also requires the natural adhesive guar gum, a powdery polymer extracted from guar beans.

In Bengaluru soil

In the current study, the authors used a more robust, native strain of the bacterium that they discovered in the soils of Bengaluru.

IISc said that after first establishing its precipitate-forming skills, the researchers were curious to see if this strain could survive in the presence of perchlorate, which can be found at levels of up to 1% in Martian soils.

In collaboration with Punyasloke Bhadury, professor at the Indian Institute of Science Education and Research (IISER), Kolkata, the team found that the bacterial cells become stressed in its presence, they grow slowly, become more circular in shape, and start clumping together into multicellular-like structures.

More proteins

The stressed bacterial cells also release more proteins and molecules in the form of extracellular matrix (ECM) into the environment. Using electron microscopy, the researchers found that more calcium chloride-like precipitates were formed, and that the ECM formed little “microbridges” between the bacterial cells and the precipitates.

“When the effect of perchlorate on just the bacteria is studied in isolation, it is a stressful factor. But in the bricks, with the right ingredients in the mixture, perchlorate is helping,” said Swati Dubey, currently a PhD student at the University of Florida and first author of the study.

As building strategy

The team said that its goal is to deploy this method as an alternative, sustainable building strategy, to rely less on carbon-intensive cement-based processes — both on Earth and Mars.

“Such technologies can also help make future Mars landing missions smoother by helping build better roads, launch pads, and rover landing sites,” Group Captain Shukla said.