Escherichia coli siderophore-induced modification of passive films on stainless steel

Abstract Modifications of the passive film on stainless steel (316 L) after Escherichia coli adhesion in the early stage of biofilm formation were investigated by XPS (X-ray Photoelectron Spectroscopy) and ToF-SIMS (Time-of-Flight Secondary Ions Mass Spectrometry). This work evidences an enrichment in Cr(III) in the presence of bacteria, which is known to improve corrosion resistance. The iron depletion is assigned to synthesis by bacteria of organic molecules (siderophore) that specifically chelate Fe3+ ions from the passive layer, followed by the reduction of Fe3+ into Fe2+ ions by the bacterium and finally release of these reduced species into the aqueous solution.