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Microbiologically influenced corrosion of metals is prevalent in both natural and industrial environments, causing enormous structural damage and economic loss. Exactly how microbes influence corrosion remains controversial. Here, we show that the pitting corrosion of stainless steel is accelerated in the presence of Shewanella oneidensis MR-1 biofilm by extracellular electron transfer between the bacterial cells and the steel electrode, mediated by a riboflavin electron shuttle. From pitting measurements, X-ray photoelectron spectroscopy and Mott-Schottky analyses, the addition of an increased amount of riboflavin is found to induce a more defective passive film on the stainless steel. Electrochemical impedance spectroscopy reveals that enhanced bioanodic and biocathodic process can both promote the corrosion of the stainless steel. Using in situ scanning electrochemical microscopy, we observe that extracellular electron transfer between the bacterium and the stainless steel is bidirectional in nature and switchable depending on the passive or active state of the steel surface.

Microbiologically influenced corrosion inhibition (MICI) of Q235 carbon steel by biomineralization was investigated via a combination of surface analysis, electrochemistry, and scanning electrochemical microscopy (SECM). The results showed that Shewanella putrefaciens used the cell walls as the nucleation sites to induce the formation of a protective biomineralized layers which contained calcite and extracellular polymeric substances on the steel surface. The potentiodynamic polarization results demonstrated that the corrosion current density (icorr value) of the biomineralized steel surface was 0.38 μA cm−2, which was less than one-tenth that of the blank steel in a sterile medium (4.86 μA cm−2) after 14 days. The biomineralized layers presented wear resistance and could self-repair after undergoing mechanical damage under microbial conditions as verified by morphological and SECM observations. This work reveals that microbial-induced carbonate biomineralization, as a MICI approach, may be considered as a reliable, low-cost, environmentally friendly corrosion inhibition strategy.