Studies on the application of microbially produced polymeric substances as protecting layers against microbially influenced corrosion of iron and steel

The contribution of biofilms to corrosion of metals and alloys, termed microbially influenced corrosion (MIC), is a challenge for research in the field of corrosion protection. In order to inhibit or prevent MIC one promising route is in principle the inhibition of the biofilm formation itself on an early stage that is to say to inhibit the adhesion of single cells. The processes of adhesion and desorption of microorganisms are known to be induced or mediated by various (bio-)molecules. Up to now, a number of biomolecules have been found that can induce desorption of already adhered cells termed biosurfactants. In other cases, bacteria have been found to release polymeric substances upon desorption from the substrate. Surface areas marked by these substances, termed bacterial footprints, are not colonized by these bacteria again.
The aim of this project is to identify and to investigate substances appropriate to inhibit the formation of biofilms of sulphate reducing bacteria (SRB), a group of microorganisms well known to severely damage metallic materials. For this purpose, extracellular polymeric substances (EPS) of various bacteria, including SRB, Lactobacilli and Pseudomonae, have been harvested and purified. The substances have been analyzed with focus on chemical groups like proteins, carbohydrates or glucuronic acids.
The EPS have been adsorbed on metal substrates in order to form layers protecting against adhesion of Desulfovibrio vulgaris. Layer formation and adhesion of bacteria were studied by epi-fluorescence microscopy (EFM) and atomic force microscopy (AFM). It was observed that the number of attached cells was significantly lower on the covered surfaces even after a couple of days when compared to pure substrates. As most of the EPS were found to be resistant against degradation by Desulfovibrio, they promise to be appropriate anti-corrosion layers.
Nevertheless, amelioration of the adhesive properties of the polymeric layers was necessary as mostly non-uniform layers lacking of long-term stability were achieved. Electrochemical results also reflected the finding of non-homogeneously covered surfaces. Attempts were made by pre-treatment of the substrate, application of additional adhesive agents and additional treatment with ultraviolet radiation in order to stabilize the EPS by cross-linking.
These results should give rise for further investigations of the influence that biomolecules like proteins or phospholipids (the latter discussed to play an important role in the corrosion inhibition of pyrite) have on the adhesion of microbial cells and MIC.