Krantz, G.P.; K. Lucas, E.L.-W. Majumder, L.T Hoang, R. Avci, G. Siuzdak and M.W. Fields (2019) Bulk phase resource ratio alters carbon steel corrosion rates and endogenously produced extracellular electron transfer mediators in a sulfate-reducing biofilm. Biofouling. [doi]:10.1080/08927014.2019.1646731 {PMID}:31402749
The presented results demonstrate that energy restriction (EAL v. EDL) greatly impacted biofilm growth and physiology of Desulfovibrio G20 biofilms grown on carbon steel. Less corrosion was observed on 316 stainless steel compared to 1018 carbon steel for both EAL and EDL condition; however, the EDL condition promoted more corrosion of 1018 steel despite a thinner biofilm with decreased aqueous sulfide levels compared to the EAL condition. However, despite being limited for electrons under the EDL condition, more biofilm-associated sulfide was observed and corrosion was increased. In addition, the increased corrosion was dependent upon biofilm interaction with the metal surface. These results suggested that the metal surface was serving as an additional electron source (i.e., Fe0). Untargeted metabolomics indicated that the EAL-grown biofilm on 1018 steel altered cysteine/methionine cycling while the EDL-grown biofilm had elevated levels of flavin-like compounds. The flavin molecules likely serve a role in extracellular electron transfer when interacting with the metal surface (Fe0) in EET-MIC (Figure 9), and this was further supported by the need for biofilm to interface directly with the metal surface for elevated corrosion. The endogenously-produced flavin molecules likely play a role to harvest electrons from Fe0 when limited for electron donor, allowing continued biofilm growth under nutrient-restricted conditions. In essence, when lactate was limiting, sulfate reduction was coupled to Fe0 oxidation at the steel surface, thus promoting increased carbon steel corrosion.
