Microbial metal reduction is a process by which microorganisms are able to deliver electrons to a solid phase that is external to the cell, this reduction plays an important role in bioremediation approaches. The gram-negative bacterium Shewanella oneidensis is the focus of this work; it is known that when oxygen becomes limiting, the expression of the outer membrane cytochrome MtrC and OmcA (needed for extracellular electron transfer) increases, however, our understanding of how this organism is able to senses the change in oxygen concentration into the environment remains unclear. The aim of this project, therefore, is to identify the redox sensor in S. oneidensis. The approach used is to screen a large number of mutants, which consists on a strain (KM001) containing mtrC-lacZ fusion in which the transposon Himar is inserted into the genome, and to find the ones with reduced b-galactosidase activity (compared to KM001) under anoxic conditions. For each mutant which meets the criteria, the transposon insertion site will be identified using arbitrary PCR, while batch cultures under anoxic and under aerobic conditions will be performed to confirm reduced activity. No relevant results were recorded relating to genes influencing the expression of MtrC, however, some interesting behaviours were detected on genes encoding for proteins AroE and AroB, which seems to be important for both aerobic and anaerobic growth.