Pb-resistant Pantoea rwandensis promotes maize's growth by altering Pb accumulation in biomass and soil Pb immobilization.

In lead (Pb)-contaminated soil, inoculating phosphate-solubilizing bacteria (PSB) to reduce the phytoavailability of Pb and to change the soil nutrients is an important way to inhibit the Pb uptake by plants. In this study, we isolated the native Pb-resistant Pantoea rwandensis from a tailings site. We employed broth culture and pot experiments to investigate the effect of the inoculation of P. rwandensis on Pb immobilization in the soil, the soil nutrients, the microbial community, and Pb accumulation in the biomass of maize (Zea mays L.). The results showed that P. rwandensis not only tolerated Pb2+ but also dissolved Ca3(PO4)2 by secreting oxalic acid, tartaric acid, lactic acid, and acetic acid, which significantly increased the amount of dissolved P, up to 567.50 mg.L-1. In the pot experiment, the application of culture filtrate, an inoculation with P. rwandensis, or a mixture of culture filtrate and P. rwandensis increased the soil residual Pb by 49.57%, 89.81%, and 41.69%, respectively, compared to the control. Consequently, the increase in the residual Pb in the soil inhibited its uptake by maize, and an inoculation of P. rwandensis or a mixture of culture filtrate and P. rwandensis decreased the accumulation of Pb in the shoot biomass of maize by 61.65% and 72.48% and in the roots of maize by 26.00% and 39.59%, respectively. Meanwhile, P. rwandensis and the mixture of culture filtrate and P. rwandensis increased the shoot biomass of maize by 54.39% and 17.86% and the root biomass of maize by 108.77% and 17.86%, respectively. A P. rwandensis inoculation increased the biodiversity of the fungal community and the abundance of Proteobacteria, Mortierella, and Sphingomonas. Our results demonstrate that an inoculation with P. rwandensis could promote the transformation of Pb fractions and a functional change in the soil bacterial community, ultimately decreasing Pb accumulation in the biomass and promoting the development of maize.