| Iron is an essential element for the growth of aerobic microorganisms, however, it is still not clear whether rhizobia in iron-polluted soil have tolerance and passivation ability to high concentrations of iron. In this study, the vanadium titanium magnetite tailings soil in Panzhihua was taken as the substrate for capturing experiment of Pongamia pinnata symbiotic rhizobium, and obtained rhizobium symbiosis nodules, and isolated and purified a total of 39 rhizobia strains from the nodules. The dominant strains PZHS20, PZHS90 and PZHS87 with strong tolerance and passivation ability were screened by testing the tolerance and passivation ability of Fe2+/Fe3+. The maximum tolerance concentration of PZHS20 to Fe2+ was 1 600 mg/L, and PZHS20 showed the highest passivation efficiency with 73.54% in 200 mg/L Fe2+ solution. The maximum tolerance concentration of PZHS90 to Fe3+ was 1 600 mg/L, while the maximum tolerance concentration of PZHS20 and PZHS87 to Fe3+ was 1 800 mg/L, and their passivation efficiency in 200 mg/L Fe3+ solution was 84.25% and 81.95%, respectively. According to phylogenetic analysis of 16S rRNA genes, PZHS20 was identified as Ochrobactrum, and both PZHS90 and PZHS87 were identified as Bradyrhizobium. The results suggested that Pongamia pinnata symbiotic rhizobia in vanadium titanium magnetite tailings soil had different degrees of Fe2+/Fe3+ tolerance and passivation ability, and the screened dominant strains could provide available strain resources for the further utilization of Pongamia pinnata and rhizobia to unite-remedy the polluted soil caused by high concentration of iron. |
