High-efficiency antimony biomineralization by Serratia marcescens: process optimization and integrated genomic–transcriptomic–proteomic analysis

Antimony is a toxic metalloid that has become a growing problem in water and soil, particularly near mining operations. It exists in nature in different forms, but one version, known as antimony(III), is especially dangerous to living things because it can disrupt the way cells generate energy and repair themselves. While nature has ways of dealing with heavy metals, including bacteria that can change toxic substances into less harmful forms, the specific steps these tiny organisms take to neutralize antimony have remained largely a mystery. Scientists have long known that some microbes can turn dissolved antimony into solid crystals, effectively locking the poison away, but they have not fully understood how the bacteria survive the toxicity long enough to do the work, or exactly how they build those crystals.

A team of researchers at Guizhou University has now peeled back the layers of this process by studying a specific bacterium they found in the waste of an antimony mine in China. They isolated a strain of Serratia marcescens, a rod-shaped microbe that proved to be incredibly tough, capable of surviving in water containing more than 250 millimoles of antimony per liter. This level of tolerance is far higher than what most other bacteria can handle. The researchers wanted to know not just that this bacterium could clean up the water, but how it managed to transform the dissolved poison into a solid, crystalline mineral called antimony trioxide. To answer this, they did not just watch the bacteria grow; they combined advanced imaging with a deep dive into the microbe's genetic instructions and the proteins it produced, creating a complete picture of the biological machinery at work.

The first step was to find the perfect conditions for the bacteria to do their job. By testing different temperatures, acidity levels, and shaking speeds, the team discovered that the bacteria worked best in slightly acidic water at a temperature of 27.7 degrees Celsius. Under these optimized conditions, the microbe removed 96.18 percent of the antimony from the water in just five days. But the real story lies in what happened during those days. Using high-powered microscopes and light-based imaging tools, the researchers watched the transformation unfold over time. They saw that the process did not happen all at once. For the first day, nothing visible appeared. Then, small, grainy clumps began to stick to the surface of the bacteria. By the second day, these clumps had grown into distinct, flaky crystals that stacked together like a pile of irregular books. It took about 36 hours for the dissolved antimony to fully turn into a solid crystal of antimony trioxide. This step-by-step observation confirmed that the bacteria first create a soft, disordered gel-like layer before it hardens into the final crystal, a pathway that differs from how crystals usually form in a test tube.

To understand how the bacteria survived such a toxic environment while building these crystals, the scientists looked inside the microbe's genetic code and its active proteins. They found that the bacterium underwent a massive internal reorganization to cope with the stress. The bacteria essentially shut down their ability to move. Genes responsible for building flagella, the tiny whip-like tails bacteria use to swim, were turned off. This was a deliberate energy-saving move. Swimming requires a huge amount of energy, and by stopping, the bacteria could redirect all that power toward pumping the toxic antimony out of their cells and building the protective crystals. Instead of swimming, the bacteria thickened their outer coating, creating a physical barrier that helped trap the antimony and gave the crystals a place to grow.

At the same time, the bacteria ramped up their internal defense systems. The toxic antimony attacks specific parts of the cell that are essential for life, particularly clusters of iron and sulfur that act as tiny batteries for the cell's energy production. The bacteria responded by aggressively hunting for iron and sulfur from their surroundings to repair these damaged parts. They also boosted their production of antioxidants, which are molecules that neutralize the harmful chemical byproducts created when the cell is under attack. The study showed that the bacteria switched their metabolism to focus on burning fats and running their energy cycle more efficiently, ensuring they had enough power to run the pumps that expelled the poison. This coordinated effort allowed the microbe to not only survive but to actively convert the liquid poison into a solid mineral.

The findings suggest that this bacterium has evolved a sophisticated strategy that balances survival with resource recovery. It does not simply tolerate the poison; it actively transforms it. By turning dissolved antimony into solid crystals, the bacteria effectively remove the threat from the water while creating a valuable mineral resource. The research provides a detailed blueprint of how this happens, showing that the process relies on a precise sequence of events: stopping unnecessary movement, repairing damaged cellular machinery, and guiding the formation of crystals on the cell surface. This discovery offers a new perspective on how nature handles heavy metal pollution and points toward the possibility of using similar biological processes to clean up contaminated sites and recover useful materials from waste.