Application potential of Comamonas testosteroni ZG2 for vegetable cultivation in nickel and cadmium polluted soil

Abstract Microbial-induced carbonate precipitation plays an important role in the remediation of heavy metal contaminated soils, but the research on microorganisms that can both induce carbonate precipitation and promote plant growth is insufficient. In this study, a nickel-cadmium-resistant bacterial strain, which can not only produce urease activity to induce carbonate precipitation but also indole-3-acetic acid (IAA) and siderophores, was isolated from heavy metal contaminated soil. It was identified as Comamonas testosteroni and named ZG2. The bacterial cells of strain ZG2 can resist high concentrations of Ni and Cd (500 mg/L and 20 mg/L, respectively) by becoming longer and thinner. The urease activity and IAA concentration in the culture broth decreased with the increase of heavy metal concentrations, while the siderophore content increased. The strain ZG2 could remove more amount of cadmium than nickel and can induce the formation of carbonate precipitation. The Cd-containing carbonate precipitate was irregularly shaped of cadmium carbonate crystals, while the Ni-containing carbonate precipitate has a regular cubic shape, but there is no crystal form. Furthermore, in soil treatment experiments, the strain ZG2 could increase the soil pH, reduce the content of available Ni and Cd in the soil and the edible parts of pakchoi, increase the biomass of pakchoi, and also promote the root system growth and development. The above results show that the strain ZG2 is valuable in the Ni-Cd contaminated soil remediation application for the safe production of vegetables.