Isolation and characterization of a cadmium-tolerant and plant growth-promoting bacterium, Brevundimonas diminuta Y01Z

Abstract:

[Objective] This study aims to isolate and characterize the bacteria with tolerance to cadmium ions and the abilities to remove cadmium and promote plant growth from the rice rhizosphere soil in Hubei province, China. [Methods] Using the dilution-plate spreading and gradient domestication methods with cadmium concentration gradients, we isolated a bacterial strain named Y01Z, which demonstrated stable growth and could tolerate 700 mg/L CdCl₂. The strain was then identified based on morphological, physiological, biochemical, and molecular biological characteristics. [Results] Y01Z was identified as Brevundimonas diminuta, with the optimal growth conditions of pH 7.0, 30 °C, and 0.5% NaCl. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed that Y01Z elongated its cells under high cadmium concentrations to ensure survival and reproduction. Moreover, it accumulated cadmium ions and transported them intracellularly. Fourier transform infrared spectroscopy indicated that Cd²⁺ bound to carboxyl, hydroxyl, carbonyl, and amide functional groups on the cell surface. After 104 hours of cultivation, B. diminuta Y01Z removed 75% of the total added cadmium, reducing the cadmium concentration from 300 mg/L to 74.73 mg/L. Additionally, the bacterium exhibited plant growth-promoting properties, including solubilization of phosphorus, production of amino nitrogen and indole-3-acetic acid, and possession of iron-chelating agents. [Conclusion] The findings suggest that B. diminuta Y01Z has significant potential for rhizobacteria-mediated remediation of cadmium-contaminated soils and the promotion of sustainable agriculture practices.