In situ immobilization of Pseudomonas sp. T1 via self-synthesized EPS for enhanced Cr(VI) reduction

Extracellular polymeric substances, crucial bacterial stress-defense matrices, exhibit exceptional heavy metal adsorption owing to their abundant functional groups. However, current application strategies typically treat EPS as isolated functional components, neglecting the biological synergy of their interactions. Conventional immobilization methods often rely on exogenous matrix materials for carrier fabrication, similarly, overlooking these interactions. Here, a novel immobilization strategy was developed wherein Pseudomonas sp. T1 was in situ immobilized within a three-dimensional network formed by cross-linking of naturally occurring EPS. The EPS-based carrier attenuated environmental stresses on immobilized bacteria and its abundant functional groups facilitated hexavalent chromium [Cr(VI)] reduction through enhanced electron transfer, thereby creating a favorable microenvironment for bioremediation. Compared with the conventional natural polymer control, the in situ immobilization carrier exhibited enhanced Cr(VI) reduction efficacy (achieving complete bioremediation at 200 mg/L Cr(VI), increased surface area, improved mass transfer efficiency, and greater thermal stability (maximum weight loss temperature increased by 20 °C). Additionally, in situ immobilization enhanced the stability of Cr(VI) bioremediation by Pseudomonas sp. T1. Under co-stress conditions of 300 mg/L Cr(VI) and 100 RPM shear force, the immobilized system achieved 71.2% bioremediation efficiency, representing a 113.3% increase over the free-cell system. When co-exposed to 40 mg/L Cd(II), the immobilized bacteria exhibited greater tolerance, with only a 1.1% inhibition compared with 41.4% in free cells. Overall, relative to conventional natural polymer-based encapsulation approaches, this self-sustaining in situ immobilization strategy streamlined the bioprocess workflow and demonstrated superior resilience to multiple environmental stressors, providing new insights into bacterial immobilization and Cr(VI) bioremediation.