Microbial fingerprint of corrosion in copper and steel alloys under varying treatments in enriched hydrogenotrophic media

The microbiological corrosion induced by methanogens has primarily been investigated in steel alloys, given their widespread use in the Oil & Gas sector, where the most significant phenomena have been observed. However, there is a growing interest in studying the metabolisms of methanogens and their effects also for other materials, due to the pivotal role these microorganisms play in the production of biogas and environmentally friendly methane as part of the energy transition. In the industrial context, copper alloys, utilized in pumps, valves, and pipelines, can also be susceptible to microbial corrosion induced by methanogen pools. In this work, the enrichment of a different pool of hydrogenotrophic methanogens and bacteria on the surface of different alloys, a pure Fe (ARMCO©, 0.02 wt.% of C), a duplex stainless steel (2205, with 22 wt. % of Cr), carbon steel (S355, 0.14 wt.% of C), pure copper, and was documented, starting from the same microbial pool. The corrosion of each material in the biotic media, in comparison with sterilized media and boiled media, were documented during replicated two-week tests. Electrochemical investigations were performed using a three-electrode cell consisting of a working electrode (test alloy), a reference electrode (saturated Ag/AgCl electrode) and a counter electrode (titanium mesh). Investigations included open circuit potential (OCP) monitoring and electrochemical impedance spectroscopy (EIS). Chemical characterizations of the corrosion products and post-experiment observations were performed by SEM and micro-Raman spectroscopy (μRS). Molecular analysis by next generation sequencing (NGS) of 16S RNA was performed by swabbing the surface of the material and identifying the microorganisms constituting the microbial communities for each case. Results revealed more significant corrosion and distinct microbial fingerprints in tests where microorganisms (bacteria and archaea) were detected, with variations depending on the material and media treatment. The discussion includes an analysis of the correlation between corrosion, the presence of specific single species, and microbial fingerprints, considering the different chemical corrosion products observed on the surfaces of metal samples exposed to various media.