Innovative and eco-friendly approaches to mitigate Microbiologically Influenced Corrosion

Microbiologically influenced corrosion (MIC) is a type of corrosion caused or accelerated by microorganisms, such as bacteria, fungi, and algae. The metabolic activity of corrosive microorganisms influences the electrochemical processes that degrade materials, especially metals, leading to pitting or crevice formation that significantly increase their deterioration rate. MIC affects various industries, including oil and gas, petrochemical, water treatment, marine, as well as any system where metals are exposed to water, soil, or humid environments. The economic burden of MIC is immense, contributing up to 20% of global corrosion-related costs, approximately US$ 2.5 trillion annually in the oil and gas sector alone, excluding its safety and environmental impacts. Counteracting MIC requires a combination of preventative and corrective measures. Sulfate-reducing bacteria (SRB) are the major contributors to MIC due to their production of hydrogen sulfide, which accelerates corrosion. Effective strategies for eliminating or controlling SRB involve both physical and chemical methods. These last face challenges such as toxicity and high disposal costs, calling for sustainable alternatives. This PhD thesis explore two innovative and eco-friendly approaches with the aim of contributing to the development of novel strategies to manage and control MIC. The first approach investigates the potential use of cinnamaldehyde, a compound with well-documented antimicrobial and anticorrosive properties. We found that low concentration of cinnamaldehyde (i.e., 12.5 µg/ml) inhibited the growth and killed Desulfovibrio vulgaris planktonic cells and almost eradicate pre-formed biofilms at 50 µg/ml, by reducing biomass (> 90 %), surface area (> 85 %) and thickness (> 60 %), with comparable efficacy to the conventional biocide, glutaraldehyde. Interestingly, we were able to show that cinnamaldehyde effectively disrupts pre-formed D. vulgaris biofilms also on representative metal coupons. These results pave the way for the future development of green sustainable strategies involving the use of cinnamaldehyde to mitigate MIC. The second approach regards the application of endolysins to control the SRB growth. Endolysins are hydrolytic enzymes encoded by bacteriophages during their lytic cycle, targeting the bacterial peptidoglycan layer, thus promoting osmotic lysis. Their fast lytic activity can also be accomplished when exogenously applied as recombinant proteins. These enzymes have garnered significant attention for their efficacy against clinically-relevant pathogens and are currently employed in clinical settings. However, their application in environmental contexts, particularly those impacted by MIC remains largely unexplored. We have selected and tested D. vulgaris-specific endolysins, demonstrating their effectiveness against D. vulgaris planktonic cells. Although preliminary, these promising results highlight the potential of endolysins in the sustainable management of MIC, bypassing the use of conventional toxic biocides. Finally, a case study highlighting the importance of microbiological investigations as a proactive MIC prevention strategy, to advocate for the incorporation of microbial community characterization into MIC management practices. Such proactive approaches will offer a potential to improve early detection and mitigation strategies, protecting marine infrastructures from corrosion-related failures.