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Materials are key for our modern communities. In particular metals play important roles in all areas of our daily life - from building materials to high tech products.
Due to the increasing consumption of metals and corresponding waste production, an elevated release into the environment takes place. Furthermore, metals in direct contact with the environment undergo corrosion leading to a release into the (aquatic) environment. Thus, lifespan of products/buildings are substantially reduced – hence unnecessary economic costs arise. Thus, research in this regard is needed within the force field of metal/material - environment.
Evaluating the environmental impact of materials as well as developing “safe” materials, new analytical methods are highly needed. One promising powerful tool is single cell-ICP-ToF-MS for multi-elemental analysis on a single cell/organism level.
Within this presentation the concept, strength as well as challenge of single cell-ICP-MS are briefly introduced. Two application examples are presented: (i) assessing the environmental impact of metals and (ii) the impact of the environment on metal-based materials and the derivation of potential environmental-friendly material protection strategies. These applications highlight the strength of new analytical approaches to explore the durability and safety of newly developed materials. Thus, analytical chemistry is one corner stone to transformation of modern society into circular economy (CEco).
(i) Diatoms are located at the bottom of the food chain. Thus, toxicological relevant metals taken up by diatoms possibly accumulate within the food web causing harmful effects. Diatoms are common test system in ecotoxicology. To investigate potential metal uptake and effects, we developed an on-line single cell-ICP-ToF-MS approach for multi-elemental diatom analysis. Our approach is a new potential tool in ecotoxicological testing for metal-based materials.
(ii) Next to classical corrosion processes, microorganisms are responsible for so called microbially influenced corrosion (MIC). MIC is a highly unpredictable process relying on interaction pathways between cells and the metal surface. Sheding light on MIC processes and derivate potential protection strategies, we applied single cell-ICP-ToF-MS for MIC research on a single bacteria/archaea level. It turned out that microorganism are taking up particular metals from alloys - thus, single bacteria-ICP-ToF-MS will enable development of corrosion protection strategies.
Microbiologically influenced corrosion (MIC) is a highly unpredictable process involving a complex group of microorganisms, including sulfate-reducing bacteria and methanogens. Standard laboratory MIC testing using static serum bottle enrichments is an easy but limited method, offering poor resolution on the biomineralization process of corrosion products. An example of this is the presumed corrosion product siderite by corrosive methanogens (Mi-MIC). Previous publications reported siderite was the sole corrosion product of M. maripaludis using metal coupons incubated under stationary conditions.
However, the formation of siderite is closely related to the surrounding environmental conditions, i.e. pH, CO2 concentration, flow and temperature. Thus, siderite as the sole corrosion product of Mi-MIC remain inconclusive and questionable. To study Mi-MIC effectively, a novel versatile multiport flow-column corrosion monitoring system (MFC) was developed. MFC allows sectional corrosion rate determination under flow conditions using different types of material, inoculum and packing material. MFC offers great flexibility, ease of operation and accurate corrosion measurements that can be combined with many other techniques. Using MFC, we studied multiple strains of methanogens and compared it with sulfate-reducing bacteria under neutral and low pH conditions. It was revealed by MFC that corrosive methanogens have equally high corrosion potential as sulfate-reducing bacteria. Additionally, siderite is not the dominant nor sole corrosion product of Mi-MIC. Thus, effective corrosion monitoring and establishing standard laboratory practices, i.e. incorporating MFC as part of regular testing process, will provide deeper understanding of MIC. This will allow further microbial electrophysiology understandings, contributing to effective mitigation strategy development.
Microbiologically influenced corrosion (MIC) on steel occurs where the presence and activity of microbes change the localized conditions on the surface of a metal substrate. For instance, metal reducing bacteria (MRB) are capable of utilizing metal compounds in the passive layer on stainless steel as electron acceptors during their metabolism. This weakening of the passive film not only leads to an acceleration of the general corrosion processes, but also increases the susceptibility of stainless steels to pitting corrosion. Even though the electron transfer mechanisms are not yet fully understood, recent research shows that the secretion of electron shuttles like flavins contribute significantly to the extracellular electron transfer (EET). Electron shuttle molecules like riboflavin (RB) or flavin mononucleotide (FMN) are secreted by MRB after the transition from planktonic to sessile mode and exist in the biofilm at low concentrations. Therefore, they are precise early phase indicators of bacterial settlement.
This project aims at clarifying the electrochemical interaction mechanisms of MRB with stainless steel surfaces, with a special focus on the role of the extracellular redox molecules. The analysis of corrosion processes as a function of chloride and flavin concentration have been performed by means of electrochemical methods. Due to the differences in their chemical structure, FMN and RB have shown significant differences in terms of their adsorption behavior and the stability of the formed films, which directly influences the electron transfer processes. Therefore, Electrochemical Quartz Crystal Microbalance (eQCM) studies have been performed on sputtered FeCr electrodes to investigate the adsorption/desorption kinetics of flavins.
The results of electrochemical studies are complemented by the analysis of the changes in the passive film chemistry and the chemical composition of the adsorbed films by means of Fourier Transform Infrared Reflection Absorption Spectroscopy (FT-IRRAS) and X-ray photoelectron spectroscopy (XPS). Changes in surface morphology have been investigated by means of Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM).The presentation will summarize our results on the degradation mechanisms of passive films on stainless steel surfaces in the presence of flavins and provide useful insights from a fundamental aspect for the understanding of the initial stages of microbiologically influenced corrosion.
Melanins are organic pigments produced by most fungi. These organisms either fix these pigments in their cell wall or secrete them into their extracellular environment to protect themselves against an array of physicochemical stresses (e.g., UV irradiation, desiccation, ...). Melanin can adsorb metals like Fe. How this affects fungal uptake of Fe and deterioration of Fe-containing minerals and metals is however less known. To study this, we use the model fungi Knufia petricola A95, a rock-inhabiting fungus known to deteriorate minerals and have melanised cell walls, and Amorphotheca resinae, able to contaminate fuel tanks, secrete melanin and corrode metals. In K. petricola, we have deleted genes involved in melanin production and Fe uptake using CRISPR/Cas. Through comparison of the geochemical signatures of these gene deletion mutants with those of the wild type (WT), we explore the specific mineral/metal deterioration mechanisms of melanised fungi.
Fe isotope signatures of the biomass of melanin- and Fe uptake-deficient mutants of K. petricola revealed that Fe adsorbed either directly onto melanin or after being reduced by Fe reductases. Importantly, once adsorbed to melanin, Fe could not be mobilised and taken up into the cell: both the WT and its melanin-deficient mutant, previously grown at Fe replete conditions, showed similar growth at Fe deficient conditions.
Olivine dissolution experiments revealed that Fe oxidation inhibits dissolution. K. petricola was able to enhance dissolution when this inhibition is strongest (at pH 6) and prevented dissolution when this inhibition is weakest (at pH 4). The fungus therefore dissolves olivine by interacting with the oxidised Fe at the olivine surface. However, Fe uptake did not seem to be involved: mutants deficient in various Fe uptake mechanism dissolved olivine at the same rate as the WT. This indicates that Fe adsorption onto melanin might play a key role. This is also shown by K. petricola’s ability to enhance olivine dissolution even further if secreting a melanin precursor and A. resinae’s corrosion of carbon steel whilst secreting melanin. Combined, our results imply that the Fe adsorbed to melanin cannot be taken up but enables fungi to deteriorate Fe-containing substrates at a higher rate.
Bei dem Vortrag werden die potentiellen mikrobiologischen Einflüsse im Falle der Lagerung von Wasserstofflagerung in unterirdischen geologischen Formationen vorgestellt, die Zusammenarbeit mit internen und auch externen Partnern. Der Fokus liegt dabei auf UGF; anaerobe Umgebungen, Sulfate reduzierenden Bakterien, methanogenen Archaea, weiterleitenden Systeme und die Kombination der Untersuchung abiotisch/biotische