@PhdThesis{duepublico_mods_00046674,
  author = 	{Thyssen, Christian},
  title = 	{Biofilm formation by the manganese-oxidizing bacterium Leptothrix discophora strain SS-1 and corrosion of stainless steel},
  year = 	{2018},
  month = 	{Aug},
  day = 	{07},
  keywords = 	{MIC; Biofilm; Manganese oxidation; Corrosion},
  abstract = 	{Nowadays it is generally accepted that microorganisms play a pivotal role in corrosion, by influencing and/or accelerating the electrochemical corrosion processes. Microbiologically influenced corrosion (MIC) is associated with biofilm formation leading to (in)direct changes of the materials surface characteristics. The biofilm is consisting of a heterogeneous matrix of extracellular polymeric substances (EPS), which is comprised mainly (in addition to water) of polysaccharides, proteins, lipids, and nucleic acids. The metabolic activity of biofilm cells and the EPS itself strongly influence the interfacial processes associated with the electrochemical processes. In this study the importance of biofilm formation and manganese oxidation for the corrosion of stainless steel was elucidate by using Leptothrix discophora SS-1 as model organism.

The growth of L. discophora SS-1 cells was tested with two different growth media with and without addition of manganese ions. It was shown that the addition of manganese ions resulted in an increased lag phase as well as an increase in generation time (from approximately 2 h to 3 h). Concomitant with the oxidation of manganese(II) ions to manganese(IV) oxides the total ATP and protein content of stationary cultures decreased up to 40 {\%} and 55 {\%}, respectively. This indicates a negative effect of manganese ions on the physiology of L. discophora SS-1.

The analysis of the (EPS) under four different growth conditions showed that L. discophora SS-1 adapts its EPS to the environmental conditions and that the EPS possess all features to facilitate biofilm formation on SS. The amount of uronic acids was increased in EPS extracted from cells grown in the presence of manganese ions. This indicates that the carboxyl groups of uronic acids might be involved in retaining manganese ions in the EPS for subsequent oxidation. Analysis of (un)saturated fatty acids identified C18:1 as a unique unsaturated fatty acid only present in EPS of cells grown in the presence of manganese ions. Additionally, the fatty acids C8:0 and C16:0 were downregulated while C12:0 was upregulated in EPS of cells grown in presence of manganese ions. The main fatty acid under all conditions was C16:1, which is in agreement with literature reports for the Leptothrix group. Fluorescent lectin binding analysis (FLBA) and EPS analysis proved to be a useful combination to identify carbohydrate monomers (in case of FLBA by the ability of lectins to bind to certain glycoconjugate residues) and to identify genuine features of the biofilm. Sorbitol, mannose and rhamnose represent the major carbohydrate constituents in EPS of L. discophora SS-1. The lectins ConA, GS-II, PWM and LPA were specific for EPS of L. discophora SS-1 under all conditions. A particular striking staining feature was observed for the lectins MPA, PWM, DBA and UEA-I. These lectins stained repeatedly a filament-like structure connecting the separated individual cells.

Analysis of contact potential difference (CPD) mapping (measurement of the surface potential) and corrosion measurements strongly indicates an effect of biofilm formation concomitant with manganese oxidation for the electrochemical degradation of stainless steel. Single cells and microcolonies were successfully labeled by fluorescence staining and in combination with Leucoberbelin blue allowed an identification of cells, microcolonies and manganese oxides on the surface. CPD mapping identified manganese oxides as cathodic areas with a negative CPD (-220 mV) and anodic areas (regularly but not always associated with identified cells) with a positive CPD (+200 mV) towards the steel surface. The potential difference of up to 420 mV between cathodic and anodic areas correlates with the 400 mV anodic shift (ennoblement) observed in open circuit potential (OCP) measurements with biofilms of L. discophora SS-1 cells precipitating manganese oxides on a stainless steel surface. The OCP shifted from initially 242 mVshe (uninfluenced by biofilms or manganese oxides) to 635 mVshe, which is well beyond the determined pitting potential (416 mVshe to 511 mVshe) of the stainless steel under the given conditions. Thus, the ennoblement of the stainless steel caused by bacteria and manganese oxides could directly be shown by this technique.},
  url = 	{https://duepublico2.uni-due.de/receive/duepublico_mods_00046674},
  file = 	{:https://duepublico2.uni-due.de/servlets/MCRFileNodeServlet/duepublico_derivate_00045902/Thyssen_Diss.pdf:PDF},
  language = 	{en}
}