Sporosarcina pasteurii is a bacterium commonly found in soil, known for its capabilities. This microbe possesses a unique natural process with utility across various fields, from construction to environmental cleanup.
A Unique Microbe’s Key Ability
The most notable characteristic of Sporosarcina pasteurii is its production of the enzyme urease. This enzyme facilitates the breakdown of urea into ammonium and carbonate ions through a process called ureolysis. This hydrolysis increases the pH, making the environment more alkaline. This elevated pH, combined with calcium ions, triggers the precipitation of calcium carbonate, a naturally occurring mineral. This process, known as microbial induced calcium carbonate precipitation (MICP), effectively forms a type of biological cement.
Transforming Construction and Environment
The biomineralization ability of Sporosarcina pasteurii offers solutions in construction. It is utilized for biocementation, strengthening loose soil by binding particles with precipitated calcium carbonate. This improves soil stability for foundations and infrastructure. The bacterium’s spores can also survive in the harsh, alkaline environment of concrete, with some strains tolerating pH levels around 11.2.
This microbe also plays a role in developing self-healing concrete, a material capable of repairing its own cracks. When cracks appear in concrete with Sporosarcina pasteurii and nutrients, dormant bacteria become active. They then precipitate calcium carbonate within the fissures, sealing cracks. This biological repair mechanism helps restore the material’s structural integrity and prolong its lifespan.
Beyond construction, Sporosarcina pasteurii shows promise in environmental remediation, immobilizing heavy metals in contaminated sites. Through coprecipitation with calcium carbonate, the bacteria bind heavy metal ions, reducing their mobility and toxicity in water or soil. Studies show high remediation rates for metals such as cadmium (Cd), lead (Pb), and zinc (Zn), often above 80% for certain concentrations. While effective for many heavy metals, its efficiency can vary for others, such as copper (Cu), where immobilization might be lower.
The Biomineralization Process
The biomineralization process begins with the urease enzyme breaking down urea. This hydrolysis reaction produces ammonia (NH₃) and carbonic acid (H₂CO₃). The ammonia then reacts with water to form ammonium ions (NH₄⁺) and hydroxide ions (OH⁻), which cause the pH of the environment to rise.
Simultaneously, the carbonic acid dissociates into bicarbonate ions (HCO₃⁻) and carbonate ions (CO₃²⁻). As the pH increases due to the hydroxide ions, the equilibrium shifts, favoring the conversion of bicarbonate to more carbonate ions. These carbonate ions then react with calcium ions (Ca²⁺) to form solid calcium carbonate (CaCO₃) crystals. The bacterial cell surface often serves as a nucleation site, facilitating the formation and deposition of these calcium carbonate crystals.