Screening of soil siderophore-producing bacteria and their activation and utilization of iron oxide

Abstract:

[Background] Iron in soil mainly exists in the form of insoluble iron oxide with low availability. The activation of iron oxide by siderophore-producing bacteria is an effective way to improve the iron utilization efficiency. [Objective] To observe the utilization of insoluble iron oxide by the siderophore-producing bacterial strains isolated from woodland soil and provide a theoretical basis for the development of microbial resources and the research on its role in nutrient regulation. [Methods] Siderophore-producing bacteria were isolated from surface soil near the tree roots by CAS detection method. The effects of temperature and pH on the growth and siderophore production of the isolates were analyzed by plate culture method. The activation effect of siderophore-producing bacteria on iron oxide was explored via oscillation balance experiments. [Results] Twelve siderophore-producing bacterial strains were isolated from surface soil near the tree roots. The results from 16S rRNA gene amplicon sequencing showed that the isolates were Pseudomonas. We selected two strains ARSB02 and CNRSB01 and analyzed their siderophore production and growth. The biomass and siderophore production of CNRSB01 were higher than those of ARSB02 under different conditions. At the time point of 22 h, the siderophore activity of ARSB02 and CNRSB01 reached 67.07% and 84.60%, respectively. The two strains could maintain good siderophore production within the range of pH 5.0-8.0 and the strongest siderophore production capacity (38.98% and 48.77%, respectively) at pH 7.0. The strains showed good siderophore production performance at 25-30℃ and the strongest siderophore production capacity (42.35% and 56.06%, respectively) at 30 ℃. Both ARSB02 and CNRSB01 grew well in goethite suspension. Strain ARSB02 had the highest biomass (OD₄₂₀value of 0.75) in the suspension with the iron oxide ratio of 0.03 g/L and strain CNRSB01 had the highest biomass (OD₄₂₀ value of 1.11) in the suspension with the iron oxide ratio of 0.015 g/L. The siderophore produced by the two strains could activate goethite. At the time point of 144 h, the activation of goethite by ARSB02 and CNRSB01 reached 12.99 μmol/L and 16.50 μmol/L, respectively. [Conclusion] The siderophore-producing bacteria isolated from surface soil near the tree roots all belong to Pseudomonas and have the ability to activate iron oxide. The results are of significance for the development and application of microbial resources in woodland soil.