Exploration of urease-mediated biomineralization for defluoridation by Proteus columbae MLN9 with an emphasis on its genomic characterization

Fluoride (F-) contamination of groundwater is a silent killer of human health that has now become a global problem. In the present study, we sought to isolate fluoride-resistant, urease producing bacteria from Fcontaminated groundwater to evaluate their potential F- biomineralization. Strain MLN9, isolated from the fluoride-contaminated village of Madhabpur in Birbhum, could resist up to 5600 mg L-1 F- concentration. Taxonomic classification of strain MLN9 based on whole genome sequence identified it as Proteus columbae MLN9. Strain MLN9 showed 88.9% of maximum F- removal efficiency at pH 8.0, 1.0 g L-1 CaCl2, and 10.0 g L-1 urea concentration. Scanning electron micrographs showed dense and porous biological crystal precipitates surrounding the surface of the bacterial cells, and the adherence of F- to the cell surface was confirmed by the energy dispersion spectrum. Moreover, the X-ray diffraction pattern showed that the F- precipitates on the cell surface were biological crystals of Ca5(PO4)3F and CaF2. Genomic analysis of strain MLN9 revealed the presence of crcB gene homologs possibly encoding F- transporters and urease regulatory proteins such as UreA, UreB, UreC, UreD, and UreG suggesting a role in defluoridation. Our findings provide new insights into the urease based MICP technology using a noble bacterium Proteus columbae MLN9 for fluoride removal.