Characteristic study of Pb2+ binding to extracellular polymeric substances from Staphylococcus epidermidis G257

Abstract

As an important toxic pollutant, lead (Pb²⁺) seriously threatens the environment and human well-being. Microbes and microbial extracellular polymeric substances (EPS) are highly effective at removing heavy metals from solutions. Herein, a Pb²⁺-tolerant strain, Staphylococcus epidermidis G257 was isolated from Guangxi of China. The strain showed strong resistance to Pb²⁺ and great Pb²⁺ adsorbability. The biosorption processes of S. epidermidis G257 and its EPS were characterized using microscopical techniques, ICP-MS, zeta potential measurement, XRD, FTIR, 3D-EEM, and XPS spectroscopy. Results showed that S. epidermidis G257 were effective in adsorbing Pb²⁺, with a biosorption efficiency of 81%. The biosorption process of Pb²⁺ was described well by the pseudo-second-order model with an adsorption capacity of 53.52 mg/g. Microscopical analyses showed that Pb²⁺ was adsorbed on the S. epidermidis surface by forming EPS precipitates. The variations in zeta potential indicated an electrostatic attraction in the Pb²⁺ adsorption process. Moreover, FTIR, 3D-EEM and XPS analyses revealed that the functional groups participating in Pb²⁺ adsorption were primarily carbonyl, carboxyl and amino groups of proteins in the EPS, which greatly facilitated Pb²⁺ adsorption by forming EPS-metal complexes. Therefore, this study unveiled that S. epidermidis G257 can be utilized as a potential biosorbent for eliminating Pb²⁺ from polluted environment.