Phytoremediation has become the most eco-friendly and commonly used way to handle heavy metal contaminated soil. Metal-resistant bacteria were widely used to assist this process by secreting beneficial phytotrophin and immobilizing heavy metal ions. However, while assisting, soil minerals might be able to adsorb metal-resistant bacteria so that induce changes in surface properties of bacteria and influence its metal-immobilization potentials. Furthermore, surface properties of Gram-negative bacteria and Gram-positive bacteria might change differently by the present of various soil minarals, and finally show different metal immobilization preference. In this study, two metal-resistant bacteria (Gram-negative bacteria Enterobacter sp.EG16 and Gram-positive bacteria Bacillus subtilis DBM) were screened from the rhisosphere of Hibiscus cannabinus, and three typical soil minerals (goethite, kaolinite and gibbsite) were chosen. The result showed that the maximum adhesion capacities of goethite, kaolinite, and gibbsite for Gram-negative bacteria EG16 were 534.54, 255.03, and 160.95 mg g−1 and for Gram-positive bacteria DBM were 417.12, 217.58, and 160.27 mg g−1 respectively. The effect of pH on the adsorption of Gram-positive bacteria DBM and Gram-negative bacteria EG16 was similar. The maximum amount of bacteria adsorption occurred at pH 4.0 and decreased with increasing pH from 4.0 to 7.0. The adsorption capacity of goethite was greater than that of kaolinite and gibbsite within the pH range of 4 to 7. The adsorption of EG16 and DBM onto goethite decreases significantly with increasing ionic strength from 1 to 100 mM K+. while ionic strength has little effect on the adsorption capacity of kaolinite and gibbsite. The trend of adsorption capacity of the two bacteria is basically the same with time. Within the first 15 minutes, two bacteria rapidly adsorbed onto the surface of three minerals. Then the adsorption is relatively slow Adsorption saturation between two bacteria and goethite is about 30 min and no significant changes were observed after 30 min. The adsorption of bacteria onto minerals can be characterized by Pseudo-second-order kinetic model. This indicates that the adsorption process of two bacteria on minerals is mainly controlled by chemical adsorption. The image of TEM and FTIR showed the same result. This study help to understand surface changes of bacteria while microbes assisting phytoremediation and give evidence to predict metal-immobilization potentials of metal-resistant bacteria.
This work was supported by the National Key R&D Program of China (2018YFD0800700); Natural Science Foundation of Guangdong Province (2018A030310127); NSFC (41807031) and the 111 Project(B18060).