Characterizing carbonate mineral-forming bacterial strains and their carbonic anhydrase activities in two coastal sabkhas

The enzyme carbonic anhydrase (CA) plays a key role in carbonate mineral formation by facilitating the interconversion between CO₂ and bicarbonate ions, thus influencing carbonate precipitation processes in natural environments. This study investigates the biomineralization potential of <i>Virgibacillus</i> strains isolated from two distinct coastal sabkhas in Qatar-Dohat Faishakh Sabkha (DFS) and Khor Al-Adaid Sabkha (KAS)-to better understand the enzymatic mechanisms driving carbonate formation in hypersaline environments. The isolated strains were evaluated for mineral formation and CA activity using three artificial media designed to simulate natural conditions: MD1, seawater-based with tryptone (SWTr), and evaporated seawater-based with tryptone (EWTr). While all strains demonstrated the ability to form minerals in MD1, only <i>Virgibacillus salarius</i> and <i>Virgibacillus marismortui</i>, both exclusive to DFS, exhibited robust mineral precipitation in SWTr and EWTr media. These strains also showed significantly higher CA activity compared to <i>Virgibacillus chiguensis</i> and <i>Virgibacillus dokdonensis</i>, which were present in both sabkhas but displayed limited mineralization and low enzymatic activity under saline conditions. Statistical analyses, including ANOVA and principal component analysis (PCA), confirmed the significant role of CA activity and salinity in modulating biomineralization potential among these strains. This research underscores the potential of CA-driven biomineralization for environmental applications. The ability of <i>V. salarius</i> and <i>V. marismortui</i> to precipitate carbonates under high-salinity conditions positions them as promising candidates for bio-based carbon sequestration technologies.