Promoting effects of ferric ions on Microcystis aeruginosa growth and arsenate accumulation and reduction at different phosphorus environments.

The effects of different dissolved organic phosphorus (DOP) associated with distinct iron conditions (iron deficient (dFe), ferric ions (Fe), and colloidal iron (CFe)) on algal growth and arsenate (As(V)) metabolism were systematically evaluated and compared in Microcystis aeruginosa. Two chemical forms of DOP (D-glucose-6-phosphate (GP) and phytic acid (PA)), as well as dissolved inorganic phosphorus (DIP), were employed as distinct phosphorus environments. The results revealed that As(V) metabolism of M. aeruginosa was more influenced by different phosphorus forms than by different iron conditions. Conversely, the release of microcystins in the media was found to be significantly more affected by the different phosphorus forms than by the iron conditions. Moreover, DOP was observed to promote arsenic (As) biotransformation, particularly the efflux of methylated As from a single algal cell, whereas DIP was found to primarily facilitate As(V) accumulation in algae. The total As metabolism amount per algal cell under PA was observed to be five times that observed under DIP and GP. The influence of iron conditions on the synthesis of algal metabolites was notable, as evidenced by the metabolites identified in algae of aliphatic (δ 1.28-1.68), humic acid-like and aromatic protein-like substances through H-NMR spectra and three-dimensional excitation-emission matrix fluorescence spectroscopy analysis. This impact was particularly notable at Fe conditions, due to the role of Fe as a micronutrient with highly bioavailable forms, which enhanced the synthesis of organic compounds in algae and promoted algal growth. Consequently, Fe could inhibit As accumulation under DIP but promote it under DOP. The obtained results facilitate a more comprehensive understanding of the combined role of different phosphorus forms and iron conditions in algal bloom outbreaks and As(V) metabolism.