The role of a melanin-like polymer in carbon steel corrosion by Amorphotheca resinae

Abstract The diesel fungus Amorphotheca resinae can influence corrosion in fuel infrastructure. We compared six isolates in their interaction with carbon steel using two carbon sources, glucose and a 7% biodiesel (B7) blend. All isolates accelerated uniform corrosion with glucose, while with biodiesel, A. resinae had no effect on uniform corrosion but inhibited localised corrosion. The secretion of a melanin-like polymer occurred only in the presence of glucose and carbon steel. Using CRISPR/Cas9-mediated genome editing, we generated and tested melanin-deficient (Δ pks1 , Δ cmr1 ) and constitutive melanin-producing strains of A. resinae . The localised corrosion rates were reduced for melanin-deficient mutants, while the uniform corrosion rates remained unchanged. Addition of secreted melanin to abiotic set-ups increased the uniform corrosion rate. These findings suggest that melanin (cell wall-bound and/or secreted) promotes localised corrosion, whereas secreted melanin accelerates uniform corrosion. The fungus-steel interaction depends both on the cellular physiology and the carbon source, highlighting the complicated role of fungi in carbon steel corrosion.