Characterization and transcriptomic analysis reveal high aluminum adsorption performance of extracellular polymeric...

Aluminum (Al) pollutants pose a significant environmental and human health risk. Microorganisms and their extracellular polymeric substances (EPS) have superior potential in the bioremediation of metals in environments. Herein, Staphylococcus epidermidis GXALA1 was isolated from highly Al-polluted soil in China and showed excellent Al³⁺ adsorption capacity. The microscopic analyses and adsorption experiments showed that 80 % of Al³⁺ was adsorbed onto the surface of S. epidermidis GXALA1 through EPS, forming granular deposits. The EPS secreted from S. epidermidis GXALA1 also displayed a strong adsorptive capacity, with a high adsorption rate of 93.88 %. The Freundlich isotherm model provided a better fit for the Al³⁺ experimental data with a higher R² of 0.957, and the pseudo-second-order model fitted the sorption kinetic processes with an adsorption capacity of 87.19 mg/g. Multispectral analyses showed that the oxygen-containing groups (CO, C-O-C, CO, and PO) of polysaccharides and the humic acid-like substances derived from EPS were involved in Al³⁺ adsorption. Meanwhile, increased polysaccharides in EPS in response to Al³⁺ stress may assure the strong Al³⁺ adsorbability of S. epidermidis GXALA1. The transcriptome sequencing analysis showed that carbohydrate metabolism (KFV35_RS01275, zwf, and glmU, LFC (log2 fold change) = 2.26, 1.99, and 1.15, respectively), glycan biosynthesis and metabolism (KFV35_RS01570, mraY, and murF, LFC = 1.53, 2.07, and 2.78, respectively), and transmembrane transporter pathways (ABC and MFS: ptsG and ugpC, LFC = 1.67 and 2.57, respectively) were significantly up-regulated, which facilitated polysaccharide synthesis and abundant EPS secretion containing the groups (CO, C-O-C, CO, and PO). This study offers novel perspectives on Al³⁺ biosorption for future applications.