Redox-active antibiotics are considered to enhance phosphorus (P) bioavailability through reductive dissolution of Fe3+ oxides and solubilization of adsorbed P. However, there has been a lack of quantitative insights into their effect on Fe3+-P with extracellular polymeric substances (EPS). Using phenazine (PHZ) antibiotics as a case study, we quantified Fe2+ production and P solubilization with batch reduction experiments and in situ reductive dissolution kinetics of Fe3+-P (amorphous and crystalline phase) by atomic force microscopy (AFM). Firstly, we captured the differences in the amount of Fe2+ production and P solubilization after exposure to different reduced PHZ-bearing solutions under simulated environmental conditions, which were further confirmed by the nanoscale surface dissolution as indicated by the formation of etch pits. In addition, Fe speciation analysis and content measurement clearly showed enhanced Fe3+ reduction in the presence of a binary combination of alginate and H2PHZ, independent of H2PHZ and Fe3+-P types. Similarly, an increase in the concentration or polymerization degree of alginate promoted the dissolution rate of Fe3+-P compared with the controls. By providing Fe3+ in a soluble organic form, the alginate-Fe3+/H2PHZ could significantly facilitate the redox reaction process relative to solid-phase Fe3+/H2PHZ and/or free Fe3+/H2PHZ, resulting in alginate-promoted reduction of solid-phase Fe3+ and solubilization of co-precipitated P. These results indicate a widespread but previously ignored role of EPS coupled with redox-active antibiotics in expanding the bioavailable pools of Fe2+ and P. We also suggest that similar studies of ligand-enhanced microbial redox of Fe-bearing minerals may reveal how ligands and microbials collectively control the redox process to affect the biogeochemistry cycling of Fe and P, and thus the eventual nutrient management for agronomical and environmental sustainability.

Alginate promotes soil phosphorus solubilization synergistically with redox-active antibiotics through Fe3+ reduction

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ACS Fall 2022

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