Exploration of functional genes in Brucella anthropi for hexavalent chromium bioremoval through gene mining: A whole genome sequencing based approach

Development of whole genome sequencing (WGS) has revolutionized in understanding the functional genes and molecular perspectives involved in the resistance of heavy metals. In the current study, VITPLJ18 bacterial isolate obtained from tannery industry showed a maximum tolerable concentration of 1300 ppm against hexavalent chromium [Cr(VI)] and specific growth rate (µmax) for the cells at 650 ppm of chromium was found to be 0.088 h⁻¹ . Whole genome analysis confirmed VITPLJ18 to be Brucella anthropi which belonged to the family Brucellaceae. Mining of VITPLJ18 genome revealed the total number of genes to be 4468, among which key resistance genes such as chrA, chrB, chrC and chrF were further analysed through comparative gene cluster analysis across various bacteria. Pangenome analysis showed both core and accessory genes contributing to metal resistance, while phylogenetic reconstruction positioned the isolate within a distinct lineage, suggesting unique adaptive evolution. Further, upregulation of chromium resistant genes such as chrA, chrB, chrC and chrF was observed in cells treated with chromium with gyrA serving as housekeeping gene. SEM-EDX confirmed structural resilience and accumulation of Cr(VI) by cells under chromium stress which corroborated with the ICPMS study showing 40 mg/g of Cr(VI) accumulation. Collectively, these findings provide substantial insights into the resistance mechanism and bioaccumulation of Cr(VI) through the upregulation of transporter and resistant genes. Therefore, VITPLJ18 can be considered as a suitable strain for the bioremoval of Cr(VI).