Culture and analysis of Australian marine samples in microbial influenced corrosion

Microbially influenced corrosion (MIC) accounts for between 10% and 20% of costsassociated with corrosion in Australia. The $6 billion AUD of damage occurs at the metalsurface in a thin biofilm formation. Formation of biofilms can occur rapidly and under many aqueous conditions, involving a large variation in bacterial species. Bacteria involved in MIC can impede or accelerate the rates of corrosion through largely unknown mechanisms involving chemical change or environmental modification, creating concentration gradients and aeration cells separated from the main environment by the biofilm. Water samples from Melbourne and Adelaide port areas adjacent to corroding structures in the environment were collected and grown. The species present over 14 days and the increase or decrease in the total corrosion product in comparison to standard abiotic corrosion was measured. Environmental factors including oxygen and mineral content in the samples was measured using ICP-MS, optical profilometry, and SEM imagery to study the metal surface and biofilm. 16S DNA analysis and biotic measurements were compared alongside to understand species involvement in corrosion product underneath biofilms. Biofilm cultures from Australian marine sites undergo changes in form and species abundance can fluctuate over a 14 day timespan. Oxygen concentration dramatically dropped as well as the biofilms forming between 24 and 72 hours after inoculation. Sites with the highest abundance of gammproteobacteria had the least amount of soluble Fe content likelydue to iron reducing bacteria (IRB) found in this class. Conditions in the cultures were well suited for sulphate reducing bacteria (SRB), which were found in sites with larger pits than abiotic corrosion. In conclusion abiotic corrosion removed more mass from mild steel samples over the course of 14 days, by covering a larger surface with small pits. Bacteria cultured from the sites demonstrated some characteristic of MIC displayed by deeper pits and trenches formed underneath a biofilm of various species of bacteria.