Lead Detoxification in Priestia megaterium

Abstract

Lead is a priority pollutant with an increasing environmental prevalence from human industrialization with deleterious consequences for both human and natural ecosystem health. In recent years, the application of lead-resistant microorganisms for bioremediation has received attention for its advantages over physiochemical remediation strategies. The bacterium Priestia megaterium has been previously observed to harbor lead resistance and accumulate lead intracellularly; however, our understanding of the mechanism for lead detoxification in this species remains incomplete. The present research employed a suite of analytical tools to investigate the mechanism of lead resistance in P. megaterium with lead sequestration in polyphosphate as the working hypothesis. Cells that were cultured in a lead-amended growth medium exhibited declining polyphosphate abundance with time, and spatial elemental analysis revealed that cells contained nanoparticles with an atomic composition similar to pyromorphite, suggesting that P. megaterium detoxifies lead by precipitating the metal with phosphate liberated from polyphosphate hydrolysis. Genomic analysis revealed that P. megaterium may export leadphosphate precipitates from the cytoplasm via the Pit or Pst system. Furthermore, lead concentrations in the growth medium increased in the presence of the bacteria relative to abiotic controls, indicating that P. megaterium can solubilize abiotic lead precipitates in its environment. Collectively, these findings concur with previous observations of lead detoxification via lead-phosphate precipitation in other bacteria and have important implications for bioremediation strategies aiming to sequester lead within bacterial cells. Notably, the release of lead nanoparticles into aqueous solution may complicate efforts to remove lead from contaminated sites using polyphosphate-accumulating bacteria such as P. megaterium, necessitating the consideration of alternative lead removal techniques for environmental remediation efforts.