Isolation and Characterization of a Novel Calcium-Precipitating Alkali-Tolerant Lysinibacillus sphaericus in Local Urban Environment

Abstract

Concrete is an extensively used construction material in infrastructures due to cost-effectiveness and durability. However, its low tensile strength makes it prone to cracking, posing persistent maintenance challenges. Traditional repair methods are often expensive and difficult to implement, especially for critical structures. Recent studies propose a potential solution involving alkaliphilic or alkali-tolerant calcium-carbonate producing bacteria in aiding concrete crack repair through microbial-induced calcium carbonate precipitation (MICP) via urea hydrolysis. Considering the adaptive nature of bacteria, we hypothesize that naturally occurring concrete-inhabiting microbes possess properties crucial for mending cracks. Therefore, this study aims to isolate and evaluate these inherent microbes and their MICP ability. Six concrete samples were collected and cultured on Alkaline Nutrient Agar for microbial isolation. Urease activity was assessed phenotypically and genotypically. MICP activity was observed and validated under Scanning Electron Microscope/Energy Dispersive Spectroscopy (SEM/EDS). Out of the 49 isolates cultured, Lysinibacillus sphaericus PUMA0250 emerges as the most promising isolate for practical implementation, showing high pH survivability in an in-house formulated concrete agar medium (pH 12.6). L. sphaericus PUMA0250 exhibited MICP activity via urea hydrolysis and harbored all crucial genes involved in urease-mediated MICP. SEM/EDS analysis confirmed the structure and composition of the produced calcium carbonate precipitate. This study demonstrates the potential of L. sphaericus PUMA0250 to be incorporated into concrete to assess its healing efficiency. Its ability to thrive in the alkaline concrete environment and produce calcium by-products may aid concrete crack repair, opening microbiological avenues for sustainable and efficient concrete repair methodologies. IMPORTANCEAlthough concrete is widely used in construction, the construction material is prone to cracking, leading to costly repairs and structural degradation. This study isolated Lysinibacillus sphaericus PUMA0250 from tropical urban concrete, that can survive the highly alkaline environment typical of concrete structures in equatorial climate. Importantly, it produces calcium carbonate, a mineral that can help in concrete repair. These findings contribute to our understanding of how microbes that naturally produce calcium carbonate by-products can be used to repair concrete. For such applications, microbes must be able to withstand extreme conditions, including high pH and low nutrient availability. Our discovery of a resilient, native isolate highlights the potential of tropical concrete microbiomes as sources for self-healing construction technologies. This work lays the foundation for more sustainable, low-maintenance building materials and opens new possibilities in microbiology-driven solutions for urban infrastructure challenges.