Arsenic Binding to Iron(II) Minerals Produced by An Iron(III)-Reducing <i>Aeromonas</i> Strain Isolated from Paddy Soil

An iron reducing bacterial strain was isolated from a paddy soil and identified as a member of the Aeromonas group by 16S rRNA gene sequence analysis. When the cells were growing with dissolved Fe(III) as electron acceptor in the presence of As(V), Fe(II) minerals (siderite and vivianite) were formed and dissolved As was removed efficiently from solution. When the cells were growing with the Fe(III) hydroxide mineral (ferrihydrite) as electron acceptor in the presence of As(V), ferrihydrite was reduced and dissolved As(V) concentrations decreased sharply. Our results demonstrated firstly that members of the Aeromonas group can reduce Fe(III) in paddy soils, and secondly that iron reduction does not necessarily lead to arsenic mobilization. However, As immobilization can occur in environments that contain significant concentrations of counter ions such as bicarbonate and phosphate.