Geobacteraceae are the most widespread microorganisms in soils and sediments in which microbial reduction of Fe(III) is an important process, either in the natural degradation of organic compounds or in their bioremediation. Geobacter species have been shown to be predominant microorganisms on electrodes harvesting electricity from the sediments. They have the capability to oxidize organic electron donor to carbon dioxide transferring the electron directly to electrodes [1]. On the other side, the ability of Geobacter sulfurreducens to reduce nitrate to nitrite or fumarate to succinate with a graphite electrode serving as electron donor has also been demonstrated [2]. Direct electron transfer to solid electrodes is achieved through periplasmic and outer membrane c-type cytochromes [3]. Outer membranes proteins and even some kind of conductive pili that serve as biological nanowires are also involved in the electron transfer chains, mainly to Fe(III) and Mn(IV) oxides [4]. The aim of this study was to assess the possible influence of G. sulfurreducens on the occurrence of corrosion of steels. Experiments were performed with pure cultures of G. sulfurreducens on mild steel (XC45) and three different kinds of stainless steels (ferritic steel, 304L, 316L). In each case the free potential increased by 200 to 300 mV after the injection of the bacteria. On the contrary, control experiments performed with the injection of the sterile medium or the bacteria suspension after filtration on a 0.2 µm filter did not induce any variation in the free potential. The presence of the cell was consequently directly responsible for the potential increase of the coupons. The occurrence or not of corrosion was discussed with respect to this potential increase and the nature of the medium. Besides, preliminary results allow assessing the possibility to use G. sulfurreducens to design protective biofilms
