Arsenic, a common highly-toxic pollutant, is mainly associated with the hydrous ferric oxides in soils and minerals. A possible mechanism for arsenic mobilization is the reductive dissolution of iron (hydr) oxides. In this paper, the possibilities of iron-reducing bacteria Shewanella oneidensis MR-1 and Shewanella sp. strain MR-4 in mobilization, oxidization and methylation of arsenic were investigated. Under laboratory conditions, the dynamics of As- and Fe-release from arsenopyrite and scorodite under microbial activities, the transformation of arsenic release from iron minerals and the environment factors affecting the arsenic release and transformation during reactions were examined. The aqueous concentrations of different forms of As were determined by a liquid chromatography-atomic fluorescence spectrometry (LC-AFS) and the new surface morphology of iron minerals was also measured and characterized using scanning electron microscopy (SEM) and X-ray diffractometry (XRD). Results indicated that As could be dissolved from arsenopyrite or scorodite and oxidized or even methylated quickly in the presence of Shewanella strains. The transformation of arsenic forms were affected by the culture temperatures, pH of environment medium, and spiked Fe(III) content in the solutions. Moreover, solid-phase analysis revealed that the morphology and mineralogy in the solid-phase products were changed, such as many wrinkle-shaped gullies were formed on surfaces of iron minerals. The amount of secondary precipitates also increased with time. The As mobility could be enhanced by the activity of dissimilatory iron-reducing bacteria in the environment. This study provides insights into in situ remediation of As pollution. (C) 2016 Elsevier B.V. All rights reserved.