Microbiol direct electron transfer: a new paradigm in anaerobic biocorrosion of steels?

Abstract

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 (Esteve-Núñez et al., 2005). On the other side, the ability of Geobacter sulfurreducens to reduce nitrate to nitrite or fumarate to succinate with a graphite electrode serving as an electron donor has also been demonstrated (Gregory et al., 2004). Direct electron transfer to solid electrodes is achieved through periplasmic and outer membrane c-type cytochromes. 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 (Holmes, 2006). The aim of this study was to assess the possible influence of G. sulfurreducens on the occurrence of corrosion of steels. In conclusion, G. sulfurreducens induced an increase in the free potential up to +0.35 V on mild steel and stainless steels, which is controlled by the initial amount of bacteria inoculated and the concentration of electron donor in solution. These preliminary results may introduce for the first time into the framework of biocorrosion the new mechanism of microbial direct electron transfer. Besides, preliminary results allow assessing the possibility to use G. sulfurreducens to design protective biofilms.