Molecular ecology and physiology of microbiologically-influenced corrosion in the deep sea

• Main Author: Yeo, Yee Phan
• Other Authors: Federico Lauro
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2024
• Subjects: Medicine, Health and Life Sciences; Microbiologically-influenced corrosion; Deep sea; Microbiology; Corrosion; Hydrostatic pressure
• Online Access: https://hdl.handle.net/10356/175702
• Institution: Nanyang Technological University

Corrosion poses a significant challenge to deep-sea operations, given the harsh and remote conditions of this environment. Mild steels, widely utilized for their affordability and favorable mechanical properties in marine applications, have not been extensively studied regarding microbiologically-influenced corrosion (MIC) in the deep sea. By employing hydrostatic pressure vessels and pump to replicate deep-sea conditions, the MIC of the marine-grade mild steel AH36 was investigated. Here, it was found that the hydrostatic pressure may influence the severity of the MIC induced by shallow-water and deep-sea sulfate-reducing bacteria (SRB). Further comparative proteomic analysis of the selected deep-sea SRB P. piezophilus indicates that differential enrichment of proteins associated with the energy metabolism pathway when incubated with mild steel. Interestingly, elevated hydrostatic pressures do not significantly alter the total proteome of deep-sea SRB, suggesting that changes in MIC behaviors may be linked to protein activity rather than the abundance of specific proteins. To validate the deep-sea MIC, enrichment cultures from field samples collected from deep sea at a depth of 1988 m. The enrichment culture established from a corroding mooring chain exhibits aggressive MIC, causing localized corrosion attacks primarily at the edges of mild steel coupons. This corrosive microbial community comprises SRB and elemental sulfur metabolizing bacteria, hinting at a potential role of elemental sulfur in mediating deep-sea MIC. Overall, this dissertation underscores the persistent threat of MIC to mild steels, even in the extreme conditions of the deep sea. While exact mechanism remains unclear, the findings here suggest that enhanced MIC is associated with stimulating anodic reaction rather than cathodic hydrogen reduction, with a potential involvement of the formation of corrosive sulfur species.