# Characterization and Proteomic Analyses of the High Cr Resistance and Removability of a Novel Lysinibacillus capsici FPHNCRA4-48 Isolated from Highly Cr-Polluted Water

## TL;DR

A new strain of Lysinibacillus capsici was found to efficiently remove chromium pollution from water, with proteomic analysis revealing key mechanisms involved in the process.

## Contribution

The study identifies a novel bacterial strain with high Cr(VI) removal efficiency and provides insights into the proteomic mechanisms underlying its bioremediation capability.

## Key findings

- The strain FPHNCRA4-48 removes over 99% of Cr(VI) at 1000 μmol/L.
- Extracellular polymeric substances (EPSs) with -OH, -NH2, and -CO-NH2 groups are key to Cr(VI) removal.
- Proteomic analysis shows up-regulation of genes related to protein synthesis and amino acid metabolism under Cr(VI) stress.

## Abstract

Chromium (Cr) is a common heavy-metal pollutant that poses a significant threat to both the environment and human health. Herein, a novel strain Lysinibacillus capsici FPHNCRA4-48, with a high Cr tolerance and removal performance, was isolated from Cr-contaminated plant water in Changde, Hunan Province. Structural characterization and proteomic analyses were performed to investigate the Cr removal performance and molecular mechanism of L. capsici FPHNCRA4-48. FPHNCRA4-48 can effectively remove more than 99% of the Cr(VI) at an initial concentration of 1000 μmol/L. The FTIR, 3D-EEM, and XPS results revealed that -OH, -NH2, and -CO-NH2 derived from extracellular polymeric substances (EPSs) were mainly involved in Cr(VI) removal. Interestingly, the protein content in the EPS increased significantly (1.32-fold) after exposure to Cr(VI). Moreover, proteomic analysis revealed that genes (rpmA, rpmI, rpmC, rplI, rpmD, deoB, deoC) related to translation and carbohydrate metabolism, and genes (pyk, icd, rpiB, eno) related to amino acid biosynthesis were all significantly up-regulated, suggesting that these pathways related to protein synthesis in L. capsici FPHNCRA4-48 were activated under Cr(VI) stress. Finally, KEGG ribosome pathway enrichment occurred. These data highlight the importance of microbial EPSs in bioremediation in Cr-polluted environments. This study identified highly efficient Cr(VI)-removing bacterial strains and conducted an in-depth analysis of the removal mechanism of their extracellular polymeric substances (EPSs), thereby providing theoretical foundations and technical support for the biological remediation of Cr(VI)-contaminated water bodies.