Siderophores, produced by Pseudomonas aeruginosa, released slightly more Fe (53.6 mu mol) than that chelated by ethylenediaminetetraacetic acid (EDTA; i.e. 43.7 mu mol) in batch experiment using As-adsorbed ferrihydrite. More importantly, about 1.79 mu mol of As was found to be associated with siderophores in the aqueous phase due to siderophore-As complex formation when siderophores were used to release As from ferrihydrite. In contrast, As was not detected in the aqueous phase when EDTA was used, probably due to the readsorption of released As to ferrihydrite. A series of pot experiment was conducted to investigate the effect of siderophores as a microbial iron-chelator on As uptake by Cretan brake fern (Pteris cretica L.) during phtoextraction. Results revealed that P. cretica, a known As hyperaccumulator, grown in the siderophore-amended soil showed about 3.7 times higher As uptake (5.62 mg-As g(-1) -plant) than the plant grown in the EDTA-treated soil (1.51 mg-As g(-1) -plant). In addition, As taken up by roots of P. cretica in the presence of siderophores seemed to be favorably translocated to shoots (i.e. stems and leaves). About 79% of the accumulated As was detected in the shoots in the presence of siderophores after ten weeks. Fluorescence microscopic analysis confirmed that As in the roots was delivered to the leaves of P. cretica as a siderophore-As complex. (C) 2014 Elsevier B.V. All rights reserved.