Study on diversity, nitrogen-fixing capacity, and heavy metal tolerance of culturable Pongamia pinnata rhizobia in the vanadium-titanium magnetite tailings

Abstract

IntroductionThe diversity, nitrogen-fixing capacity and heavy metal tolerance of culturable rhizobia in symbiotic relationship with Pongamia pinnata surviving in vanadium (V) - titanium (Ti) magnetite (VTM) tailings is still unknown, and the rhizobia isolates from the extreme barren VTM tailings contaminated with a variety of metals would provide available rhizobia resources for bioremediation.MethodsP. pinnata plants were cultivated in pots containing the VTM tailings until root nodules formed, and then culturable rhizobia were isolated from root nodules. The diversity, nitrogen-fixing capacity and heavy metal tolerance of rhizobia were performed.ResultsAmong 57 rhizobia isolated from these nodules, only twenty strains showed different levels of tolerance to copper (Cu), nickel (Ni), manganese (Mn) and zinc (Zn), especially strains PP1 and PP76 showing high tolerance against these four heavy metals. Based on the phylogenetic analysis of 16S rRNA and four house-keeping genes (atpD, recA, rpoB, glnII), twelve isolates were identified as Bradyrhizobium pachyrhizi, four as Ochrobactrum anthropic, three as Rhizobium selenitireducens and one as Rhizobium pisi. Some rhizobia isolates showed a high nitrogen-fixing capacity and promoted P. pinnata growth by increasing nitrogen content by 10%-145% in aboveground plant part and 13%-79% in the root. R. pachyrhizi PP1 showed the strongest capacity of nitrogen fixation, plant growth promotion and resistance to heavy metals, which provided effective rhizobia strains for bioremediation of VTM tailings or other contaminated soils. This study demonstrated that there are at least three genera of culturable rhizobia in symbiosis with P. pinnata in VTM tailings.DiscussionAbundant culturable rhizobia with the capacity of nitrogen fixation, plant growth promotion and resistance to heavy metals survived in VTM tailings, indicating more valuable functional microbes could be isolated from extreme soil environments such as VTM tailings.

Evaluation of the control efficacy of antagonistic bacteria from V-Ti magnetite mine tailings on kiwifruit brown spots in pot and field experiments

“…Extremophiles are relevant to a broad range of fields, spanning biotechnology, biodegradation, bioremediation, biorefining, and astrobiology, as well as various industries, such as agriculture and the production of pharmaceuticals, food, cosmetics, and textiles (Kochhar et al, 2022 ). V-Ti magnetite mine tailings can harbor an abundance of plant-growth-promoting microorganisms, including nitrogen-fixing rhizobia and indoleacetic acid-producing, siderophore-secreting, and heavy metal-tolerant microbes (Yu et al, 2014 ; Shen et al, 2023 ). In the present study, 18 bacterial strains isolated from the V-Ti magnetite mine tailings displayed various antagonistic effects on kiwifruit brown spot disease.…”

“…The vanadium (V) and titanium (Ti) magnetite mine tailings found at Panzhihua in Sichuan, China, contain various harmful components, including heavy metals, most notably. The harsh environment has fostered the presence of beneficial microorganisms, such as plant-growth-promoting bacteria and heavy-metal-resistant microbes (Yu et al, 2014 ; Shen et al, 2023 ). However, there is no research on whether microbial strains with antagonistic effects on pathogens like C. cassiicola can be identified from among such tailings.…”

Heavy Metal Contamination in Soil: Implications for Crop Resilience and Abiotic Stress Management

“…While mycorrhizal fungi and nitrogen-fixing bacteria can mitigate the effects of toxic metals/metalloids on plants, high concentrations of these metals can disrupt the symbiotic relationships, reducing plant growth and nutrient uptake [24,[109][110][111].…”

“…Furthermore, the diversity, nitrogen-fixing capacity, and toxic metal/metalloid tolerance of culturable rhizobia associated with leguminous plants, such as Pongamia pinnata, have been studied, demonstrating that these bacteria can survive in toxic metal/metalloid-contaminated environments and continue to provide the essential service of nitrogen fixation to their host plants [110]. Figure 2 summarizes the strategies of these microorganisms for enhancing plant resilience and mitigating the effects of toxic metals/metalloids.…”