Carbon source starvation triggered more aggressive corrosion against carbon steel by the Desulfovibrio vulgaris biofilm

• We demonstrate that starved Desulfovibrio vulgaris biofilms are more aggressive.
• Carbon starvation increases carbon steel weight loss caused by D. vulgaris.
• Moderate carbon starvation causes deepest pits.
• Severe carbon starvation causes broader but shallower pits.
• Extreme carbon starvation reduces weight loss due to severely weakened biofilm.

The study of microbiologically influenced corrosion (MIC) has long been plagued by a lack of clear understanding of MIC mechanisms. In this work, bioenergetics was used to explain why and when sulfate-reducing bacteria (SRB) became aggressive toward carbon steel. Fe2+/Fe0 and acetate + CO2/C3H5O3− (lactate) have similar reduction potentials at pH 7 (−447 mV vs. −430 mV). Bioenergetically, Fe0 oxidation releases more energy than lactate oxidation, but Fe0 cannot provide organic carbons needed for growth. If there is insufficient carbon source that can diffuse from the bulk fluid to an iron surface, sessile cells at the bottom of an SRB biofilm on the surface may suffer from local carbon source starvation. In this work, mature Desulfovibrio vulgaris (ATCC 7757) biofilms initially grown in ATCC 1249 culture medium on C1018 carbon steel coupons were subjected to starvation by switching to fresh culture media with 0% (control), 90%, 99% and 100% less organic carbon, respectively. It was found that 90% and 99% carbon reductions increased weight loss significantly. Experimental data also showed that 90% carbon reduction caused a 10 μm maximum pit depth, largest among all other cases, while 99% carbon reduction yielded the highest specific weight loss of 0.0019 g/cm2.