Bioenergetics Explains When and Why More Severe MIC Pitting by SRB Can Occur

The detection and prediction of microbiologically influence corrosion (MIC) have long been plagued by a lack of basic MIC mechanisms. In this work, bioenergetics is used to investigate why sulfate reducing bacteria (SRB) become aggressive. The electrochemical standard reduction potentials of Fe2+/Fe and acetate + CO2/lactate are very close. This means that bioenergetically Fe oxidation is at least as favorable as lactate oxidation, except that the former does not provide organic carbons for cell growth. In the stationary cell growth phase, Fe oxidation generates energy in the form of ATP used by SRB as maintenance energy when it is coupled with dissimilartory sulfate reduction. This work presents experimental data proving that when the sessile SRB cells on an iron surface are starved of organic carbons, they will turn to Fe oxidation and thus cause more severe MIC pitting. Biofilm morphology also plays a critical role in MIC pitting. Loose biofilms allow better mass transfer of organic carbon to the iron surface, while dense biofilms restrict the mass transfer and thus result in organic carbon starvation that leads to more severe MIC pitting. Other aspects of MIC mechanisms will also be investigated.