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. • A heavy metal-resistant bacteria, Comamonas testosteroni strain ZG2, was isolated, with the ability to produce urease enzyme, indole-3-acetic acid (IAA), and siderophores. • The bacterial strain ZG2 could induce the Cd-containing carbonate mineral and remove more than 60% of Ni 2+ and Cd 2+ concentrations in the fermentation broth. • Strain ZG2 can immobilize heavy metals (Ni and Cd) from the polluted soil, reduce the Ni and Cd available contents in the soil and the edible parts of Pakchoi, and promote the growth of Pakchoi.