The key role of extracellular polymeric substances from indigenous Bacillus sp. X-113 in facilitating uranium immobilization

Uranium (U) contamination poses a serious threat to both humans and ecological environment, and the interaction between microorganisms and U can reduce the mobility of U. In this study, the impact of EPS secreted by indigenous Bacillus sp. X-113 on U immobilization was systematically investigated. The obtained results showed that the presence of EPS facilitated U immobilization by Bacillus sp. X-113, and U removal rate of Bacillus sp. X-113 with EPS was 19.39% higher than that of Bacillus sp. X-113 without EPS. U immobilization by Bacillus sp. X-113 was a monolayer adsorption on the cell surface through chemical adsorption, and Bacillus sp. X-113 could induce the formation of amorphous U-P precipitates. EPS contains abundant functional groups that provide more binding sites for U immobilization, especially phosphate groups. The products of U containing precipitates are more pronounced after U immobilization by Bacillus sp. X-113 in the presence of EPS, and EPS has an effect on the distribution of precipitates. Moreover, the protein-like and humic acid-like substances in EPS enhance the U immobilization by Bacillus sp. X-113. This study provides a new perspective and in-depth understanding of the interaction between microorganisms in mining areas and U from the perspective of EPS.