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

• XPS and ToF-SIMS techniques were applied to understand biofilm-surface interaction. • The effect of Escherichia coli on the passive film composition has been explored. • Escherichia coli adhesion leads to a Cr enrichment of the passive film. • A mechanism involving bacterial metabolism explains passive film modifications. 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. [ABSTRACT FROM AUTHOR]