Abstract
(1) Background: Rhizobia can promote plant growth by providing essential nutrients such as NH(4)(+) and PO(4)(3-); thus, rhizobia that can tolerate the stress of heavy metals will be conducive to the phytoremediation of heavy-metal-contaminated soils. Therefore, understanding the dominant heavy-metal-tolerant rhizobia that can be cultured is important for the establishment of an indigenous legume-rhizobia symbiotic remediation system; (2) Methods: Here, we investigated nifH gene diversity in culturable rhizobia from black locust (Robinia pseudoacacia L.) grown in cadmium (Cd)-contaminated soils using high-throughput sequencing.; (3) Results: A total of 16 genera and 26 species were identified from the cultures of root nodules of black locust exposed to five Cd levels. Cadmium did not show a significant effect on the abundance, diversity, and evenness of the culturable rhizobia community. However, Cd significantly affected the community structure of culturable rhizobia containing nifH. Mesorhizobium, Sinorhizobium, and Rhizobium were the absolute dominant genera present in the cultures under five Cd treatments. Additionally, Cd significantly affected the relative abundance of Azohydromonas, Xanthobacter, Skermanella, Bradyrhizobium, Paenibacillus, and Pseudacidovorax in the cultures. Soil pH, total Cd, DTPA-Cd, and C/H ratio were the significant factors on culturable rhizobia community.; (4) Conclusions: Cd showed a negative effect on nifH gene community of culturable rhizobia from black locust, which will provide insight into the selection of excellent strains that can promote phytoremediation of heavy-metal-contaminated soils.