Endophytic bacteria in Halogeton glomeratus from mining areas are mainly Sphingomonas pseudosanguinis, with a Cyanobacteria moving from roots to leaves to avoid heavy metals

Abstract

In the cold and arid mining areas of Northwest China, Halogeton glomeratus C. Meyer (Amaranthaceae) is a promising plant for the remediation of heavy metal pollution. In this study, samples correspond to a gradient of nickel and copper pollution, and this study aims to analyze the characteristics of endophytic bacteria in H. glomeratus under such pollution gradients. Samples of the plant H. glomeratus and their corresponding rhizosphere soil were collected from a smelting area, a mining area, and a control area within the Jinchang mine. In mining and smelting areas, Ni in H. glomeratus rhizosphere soils was 95 and 6 times, and Cu was 40 and 94 times higher than control area. Ni in H. glomeratus from these areas was 27 and 4 times, and Cu was 4.2 and 4.6 times greater than control area. The endophytic bacteria predominantly found in H. glomeratus from nickel-copper mining regions was Sphingomonas pseudosanguinis. Our findings might corroborate the notion that heavy metal stress in the soil can markedly facilitate the migration of an unclassified second most abundant species of Cyanobacteria, residing within the roots of H. glomeratus, to aerial tissues, where the stress from heavy metals was diminished. RDA indicated that the migration and enrichment of nickel and copper into the tissues of H. glomeratus in smelting and mining areas influenced changes in the community structure of endophytic bacteria. Under varying levels of nickel and copper stress, endophytic bacteria underwent alterations in their metabolic characteristics, aiding H. glomeratus in withstanding heavy metal stress through processes such as lipid, nucleotide, and amino acid metabolism, xenobiotics biodegradation and metabolism, protein folding, sorting, and degradation, as well as replication and repair. The identification of plant growth-promoting traits, including the ability to release phosphorus, produce IAA and ACC deaminase, and exhibit tolerance to nickel and copper, among culturable dominant strains, had shown that Pseudomonas oryzihabitans K2l-2-LB and Pseudomonas putida K2r-3-R2A possess significant potential for application. These strains could be effectively utilized as microbial inoculants to promote plant growth during the restoration of vegetation in nickel and copper-contaminated mine sites.