Proteins dominate in the surface layers formed on materials exposed to extracellular polymeric substances from bacterial cultures.

The chemical compositions of the surface conditioning layers formed by different types of solutions (from isolated EPS to whole culture media), involving different bacterial strains relevant for biocorrosion were compared, as they may influence the initial step in biofilm formation. Different substrata (polystyrene, glass, steel) were conditioned and analyzed by X-ray photoelectron spectroscopy. Peak decomposition and assignment were validated by correlations between independent spectral data and the ubiquitous presence of organic contaminants on inorganic substrata was taken into account. Proteins or peptides were found to be a major constituent of all conditioning layers and polysaccharides were not present in appreciable concentrations; the proportion of nitrogen which may be due to DNA was lower than 15%. There was no significant difference between the compositions of the adlayers formed from different conditioning solutions, except for the adlayers produced with tightly bound EPS extracted from D. alaskensis.

Influence of respiratory substrate in carbon steel corrosion by a Sulphate Reducing Prokaryote model organism.

Sulphate Reducing Prokaryotes (SRP) are an important group of microorganisms involved in biocorrosion processes. Sulphide production is recognized as a fundamental cause of corrosion and nitrate is often used as treatment. The present work analyses the influence of respiratory substrates in the metal, from off-shore installations, SRP influenced corrosion, using Desulfovibrio desulfuricans ATTC 27774 as model organism, since this can switch from sulphate to nitrate. Open Circuit Potential over 6days in different conditions was measured, showing an increase around 200 and 90mV for the different media. Tafel plots were constructed allowing Ecorr and jcorr calculations. For SRP in sulphate and nitrate media Ecorr values of -824 and -728mV, and jcorr values of 2.5 and 3.7µAcm(-2), respectively, were attained indicating that in nitrate, the resultant corrosion rate is larger than in sulphate. Also, it is shown that the equilibrium of sulphide in the solution/gas phases is a key factor to the evolution of corrosion Nitrate prevents pitting but promotes general corrosion and increases the corrosion potential and iron dissolution 40 times when compared to sulphate. Our results demonstrate that nitrate injection strategy in oil fields has to be considered carefully as option to reduce souring and localized corrosion.