# Unraveling the resistance mechanism for Shigella under stress of heavy metal Pb(II)

## TL;DR

A Shigella strain isolated from mining soil effectively removes lead through biosorption, with mechanisms involving surface complexation and precipitation.

## Contribution

Isolation and characterization of Shigella sp. D5, revealing its Pb(II) resistance and biosorption mechanisms.

## Key findings

- Shigella sp. D5 achieved 82% Pb(II) removal under optimized conditions.
- Pb(II) was precipitated as Pb5(PO4)3OH and Pb5(PO4)3Cl on bacterial surfaces.
- Biosorption followed pseudo-second-order kinetics and fit Langmuir/Freundlich isotherm models.

## Abstract

Lead is considered a main pollutant that is found in air, soil, and water, which is a dangerous waste and extremely toxic to any living organism. The use of micro-organisms is the most successful approach to remediate heavy metals from the environment due to their efficacy and financial viability. Shigella sp. D5 was isolated from a mining soil, which was found to be well capable of removing the heavy metal Pb(II). In the present research, biosorption of Pb(II) from aqueous solution via D5 living mass was described. Factors affecting biosorption efficiency, such as adsorbent dose, initial lead concentration, temperature, pH, and contact time, were investigated. The optimum levels of pH, initial Pb(II) concentration, temperature, and contact time were 7, 200 mg/L, 35°C, and 24 h, respectively. Under the optimized adsorption conditions, the removal rate of lead reached 82% when the initial concentration of lead was 50 mg/L. Both Langmuir and Freundlich isotherm models were fitted well with the equilibrium experimental data. The kinetic results showed that the sorption data closely followed a pseudo-second-order kinetic model. The micro-adsorption mechanism of Pb(II) was investigated by SEM, FTIR, XRD, and XPS techniques. It demonstrated that the anionic components like phosphate, oxhydryl, and chloride groups can remove Pb(II) through strong surface complexation and electrostatic attraction for D5. The strain D5 could transfer lead ions into highly insoluble compounds Pb5(PO4)3OH and Pb5(PO4)3Cl on the bacteria surfaces. All results indicated that it was feasible to effectively remove Pb(II) by using the Shigella sp. D5. This study elucidates the adsorption properties and resistance mechanism of Shigella for Pb(II).

Microbially mediated remediation is a promising approach for heavy metal pollution control due to its cost-effectiveness, environmental compatibility, and adaptability. Understanding the mechanisms of microbial adsorption and resistance to heavy metal is critical for guiding practical bioremediation efforts. In this study, we isolated a highly lead-resistant Shigella sp. D5 from coal mine-contaminated soil. Although Shigella are frequently detected in heavy metal-polluted environments, their adsorption capacities and the resistance mechanism to Pb(II) remain poorly characterized. Our findings advance the understanding of microbial strategy for heavy metal remediation and highlight their role in heavy metal mineralization processes.