Biofilm mediated mineral alteration of limestone by Bacillus cereus and sulphate reducing bacterial consortia: impacts on quality grading, stability, and composition

Abstract

Microbial mediation of mineral transformation plays a vital role in both geochemical processes and industrial applications. This study investigates native bacterial communities from Upper Cretaceous limestone fossil deposits in Ariyalur, Tamil Nadu, India, focusing on their role in altering the composition of the limestone. A total of eleven morphologically distinct bacterial isolates and a sulphate-reducing bacterial (SRB) consortium were isolated and screened for urease production and sulphate-reducing ability under site-specific conditions. Biofilm formation, evaluated using confocal laser scanning microscopy (CLSM), revealed isolate-specific differences in biofilm architecture. The urease-positive isolate (CS4), Bacillus cereus, produced a thick matrix-rich biofilm (81.34 ± 0.84 µm) associated with mineral precipitation. In contrast, the SRB consortia formed a thinner biofilm (42.18 ± 0.87 µm), which promoted mineral dissolution. SEM/EDX and XRD analysis confirmed significant changes in the limestone texture and mineral composition of CS4-treated samples, including increased calcium content (∼6.39%) and reduced phosphorus (∼11.68%), sulphur (∼2.33%), and chlorine (∼3.07%), which are elements detrimental to cement quality. The study also indicates that sulphate reduction may be an important factor in the genesis of microbial-mediated limestone fossil formation. These findings suggest that microbial biofilm dynamics and urease-mediated processes can selectively enhance limestone quality, providing new insights into selective mineral leaching, biocalcification, and microbial–mineral interactions with potential industrial relevance.