To study the extra-cellular electron transfer process by which electrons can be transferred from microbial cells to Fe(Ⅲ) oxides

two experiment systems were established: traditional anaerobic cultivation system and novel microbial fuel cell system. Comparing the data gathered from these two systems

it was proposed that direct contact was a very important way for ferric oxides reduction by Geobacter metallireducens.Electron shuttles played a less important role after most of the surface of mineral oxides were covered by microorganisms

and the reduction rate was to some extent related to the surface area of solid electron acceptors.