Speciation of Arsenic in Medium Containing Bacterial Strains of Lysinibacillus boronitolerans and Bacillus cereus: Mechanism of Arsenic Removal.

Environmental issues have become increasingly critical and frequent in recent decades due to excessive population growth and intensified industrial and mining activities. Among the most concerning contaminants is arsenic (As), a toxic element associated with severe environmental and human health risks. This study aimed to investigate the bioremediation potential of the bacterial strains Lysinibacillus boronitolerans and Bacillus cereus, elucidating the mechanisms involved in arsenic transformation and removal under controlled conditions. The strains were cultivated in liquid medium containing known concentrations of As(III) and As(V), and the chemical forms of arsenic were analyzed using High-Performance Liquid Chromatography coupled with Inductively Coupled Plasma Mass Spectrometry (LC-ICP-MS). The production of exopolysaccharides (EPSs) and arsenite oxidase activity were also evaluated. Morphological and elemental analyses were performed using scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS). The bacterial strains exhibited significant 69.38-85.72% reductions in arsenic concentration and approximately 14-15% volatilization rates. No EPS production or arsenite oxidase activity was detected, suggesting alternative detoxification pathways. SEM-EDS analyses revealed intracellular accumulation of arsenic, while LC-ICP-MS speciation confirmed interconversion between As(III) and As(V), indicating the action of methylation-dependent detoxification and membrane transport mechanisms. The findings demonstrate that L. boronitolerans and B. cereus possess efficient arsenic resistance and transformation mechanisms, even without conventional enzymatic pathways. These strains show strong potential for use in sustainable bioremediation of arsenic-contaminated environments, particularly in regions affected by mining activities.