Alleviating Arsenic Toxicity on Enterobacter asburiae AT40 Cells Using Ferric Compounds for Potential In Situ Arsenic Bioremediation Technology

Abstract

The detoxification of arsenic in terrestrial waterbodies through an in situ bioremediation process has great potential to alleviate the burden of arsenic-triggered diseases in humans and animals. Bacteria have been touted as suitable biocatalysts for aquatic bioremediation processes due to their fast growth, robust metabolic powerhouse enacting catalysis of a broad range of pollutants, and survival in diverse ecological niches. The arsenic detoxification mechanism in a few bacteria has been explored, while an insightful investigation of their interactions with arsenic compounds and improvement in arsenic tolerance for a resilient bioremediation process under the toxic environment is yet to be adequately pursued. Herein, an arsenic-resistant bacterial strain with a minimum inhibitory arsenic concentration of ∼1678 ppm was isolated from a wastewater body and identified as Enterobacter asburiae following 16S rRNA gene sequence analysis. Energy-dispersive X-ray analysis revealed significant adsorption of arsenic (arsenite 0.7 wt %) on the bacterial cell surface. X-ray photoelectron spectroscopic analysis confirmed the conversion of highly toxic As3+ into a less toxic As5+ state, with an overall conversion of 95.83%. In an As3+-spiked culture condition, the bacterial cells secreted iron-chelating molecules, such as desferrioxamine, as revealed from the liquid chromatography mass spectrometry analysis. These secreted compounds may facilitate iron sequestration into the cells to withstand the toxic effect, as demonstrated by the cell viability studies through fluorescence activatedcell sorting analysis of the 100 ppm As3+-treated culture broth cotreated with ferric compounds (0.6 mM), leading to a 51% increase in the active cells. This study thus demonstrated how the viability of arsenic-detoxifying endemic bacterial cells under high arsenic stress conditions could be improved by supplementing ferric compounds in the media for their resilience growth and arsenic bioremediation potential.