The mutual effects of Acidiphilium cryptum, nine ligands and dissolved iron on jarosite dissolution were studied in a 2(3) full factorial experiment. Ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA) and oxalic acid were able to dissolve jarosite chemically, but bacterial action enhanced this dissolution; from 88 +/- 1, 46 +/- 0 and 36 +/- 0 mu mol/L d to 129 +/- 3, 177 +/- 5 and 106 +/- 14 mu mol/L d, respectively. Oxalate and NTA exhibited a synergistic effect with dissolved iron and bacteria that may be explained by a model in which iron complexes behave as redox mediators in the microbial respiration in which jarosite, a solid substrate, serves as terminal electron acceptor.