Wastewater containing low concentrations of rare earth ions not only constitutes a waste of rare earth resources but also threatens the surrounding environment. It is therefore necessary to develop environmentally friendly methods of recovering rare earth ions. The spores produced by Bacillus are resistant to extreme environments and are effective in the bioadsorption of rare earth ions, but their adsorption behaviors and mechanisms are not well understood. In this study, the cells and spores of Bacillus subtilis PS533 and PS4150 were used as biosorbents, and their adsorption of terbium ions was compared under different conditions. The adsorption characteristics of the spores were investigated, as were the possible mechanisms of interaction between the spores and rare earth ions. The results showed that the PS4150 spores had the best adsorption effect on Tb(III), with the removal percentage reaching 95.2%. Based on a computational simulation, SEM observation, XRD, XPS, and FTIR analyses, it was suggested that the adsorption of Tb(III) by the spores conforms to the pseudo−second−order kinetics and the Langmuir adsorption isotherm model. This indicates that the adsorption process mainly consists of chemical adsorption, and that groups such as amino, hydroxyl, methyl, and phosphate, which are found on the surface of the spores, are involved in the bioadsorption process. All of these findings suggest that Bacillus subtilis spores can be used as a potential biosorbent for the recovery of rare earth ions from wastewater.

Plant growth-promoting rhizobacteria (PGPR) play an important role in promoting plant growth and increasing crop yield. Bacillus cereus DW019, which was previously isolated from an ion-absorbed rare-earth ore of Ganzhou in Southeastern China, has been considered as a PGPR due to its production of indole-3-acetic acid (IAA), ammonia and siderophore, but its promoting effect on plants remains poorly understood. In this study, autoclaved dead cells and viable cells of Bacillus cereus DW019 at different concentrations were inoculated into pot-cultivated cherry tomato (Lycopersicon esculentum) to investigate the promoting effect on plant growth and yield. A total of 70 days after inoculation, the plants and fruits of cherry tomato were harvested, and their growth indicators, yields, and nutrients were measured. The results showed that biomass, stem thickness, plant height and root length were significantly promoted and that the vitamin C, soluble sugar and soluble protein were significantly increased. Inoculation with Bacillus cereus also modulated the rhizospheric microbial community diversity and structure, especially the proportions of Proteobacteria and Actinobacteriota, which in turn improved the plant height, fresh weight, nutritional quality and rhizosphere soil bacterial diversity of cherry tomato. All the findings suggest that Bacillus cereus DW019 is beneficial to the growth of crops and improves the yield of cherry tomato, suggesting that Bacillus cereus DW019 could be developed into a potential biofertilizer to be used as an agricultural inoculant to increase crop yield and improve the soil ecosystem.

Biosorption of rare earth ions by growing cells of Bacillus species has been well studied and has attracted attention for possible hydrometallurgy applications. However, the interaction of spores from Bacillus species with rare earth ions has not been well studied. We investigated here the adsorption and/or desorption of two rare earth ions, Tb ³⁺ and Dy ³⁺ , by Bacillus spores, the location of the adsorbed ions, and the spore properties after ion accumulation. The significant adsorption of rare earth ions on the surfaces of Bacillus spores and the ions’ rapid release by a chelator could allow the development of these spores as a biosorbent to recover rare earth ions from the environment.