Biomodification and biodeterioration of carbon coatings by fungal strains

• Structure of carbon coatings is strongly modified by the growth of some fungi.
• XPS and FTIR revealed biooxidation and biohydrogenation of the graphite phase.
• Graphite induces fungal biosynthesis of some specific oxidoreductases.
• Laccase and other oxidoreductases play a crucial role in DLC film biodeterioration.
• The quality of carbon coatings needs to be controlled by tests using fungal strains.

Over the past years, surface protection by hard carbon coatings has been increasingly applied in many fields. This study aimed to characterize changes in the properties of carbon coatings brought about by the growth of fungi (the first report about these processes was published by Kaczorowska et al., Nanodiam, PWN, 2006, 99–116). Alterations in the structure of diamond-like carbon (DLC) and nanocrystalline diamond (NCD) coatings, examined by Raman spectroscopy, XRD, XPS, and FTIR, were found to be caused by the processes of oxidation (incorporation of oxygen atoms) and reduction (hydrogenation) occurring within graphite carbon and amorphous carbon domains (components of the surface layer of the tested coatings along with the diamond domain). Determination of the activity of selected enzymes synthesized by the studied strains of filamentous fungi revealed that the observed biomodification and biodeterioration processes involved, among others, laccase, Mn-dependent peroxidase, two catechol dioxygenases, and esterases. The biosynthesis of these enzymes by fungi was enhanced when graphite was added to their culture media. Because of the high risk of fungal infections, the quality of carbon coatings should be routinely controlled by standard microbiological tests employing suitable strains of filamentous fungi (e.g., Aspergillus niger) and yeasts synthesizing enzymes that attack carbon materials.