Functional and genomic characterization of halotolerant Bacillus paramycoides MSR1 for MICCP-based durability enhancement of cementitious materials under saline conditions.

Abstract

Microbially induced calcium carbonate precipitation (MICCP) is a sustainable strategy for improving the mechanical strength and durability of cementitious materials through biologically mediated mineral precipitation. The performance of most ureolytic bacteria declines under saline conditions, limiting their use in marine environments. This study evaluates the genomic and functional adaptation of the halotolerant ureolytic bacterium Bacillus paramycoides MSR1, isolated from Sambhar Lake, Rajasthan, India, for MICCP-based applications in saline construction environments. B. paramycoides retained high urease (590 U/mL) and carbonic anhydrase (90 U/mL) activities and precipitated 180 mg/100 mL of calcium carbonate after 7 days at 3.5% NaCl concentration, equivalent to seawater salinity, while continuing to demonstrate effective biomineralization up to 5% NaCl concentration. Therefore, 3.5% NaCl was selected for mortar casting and curing to simulate marine conditions. Incorporation of B. paramycoides in mortar specimens cast and cured under 3.5% saline conditions (BS) increased 28-day compressive strength by 15.28% and reduced sorptivity from 0.0043 to 0.0007 cm s^- 1/2 compared to control mortar (W). FE-SEM/EDX analysis confirmed CaCO₃ deposition in mortar matrix of BS specimens. Whole-genome sequencing produced an assembly of 5,453,313 bp with N₅₀ of 129,914 bp, comprising 5,832 coding sequences. Genome annotation identified urease structural (ureA, ureB, ureC) and accessory (ureD, ureE, ureF, ureG) genes along with carbonic anhydrase genes and a broad range of salt adaptation genes involved in compatible solute biosynthesis and transport, ion homeostasis, mechanosensitive channels and stress response regulation, providing molecular insight into its biomineralization potential. The physiological, material and genomic analyses demonstrate that B. paramycoides can sustain biomineralization under saline stress, highlighting its potential for developing durable and self-healing cementitious materials for coastal and marine infrastructure.