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Eingeladener Vortrag
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In the modern world there is an increased understanding that design and performance monitoring of materials have to be tested in connection to chemical, physical and (micro)biological challenges. A systematic study on how biofilms interact with materials and what could be done to engineer biofilms and/or materials in order to maximize the resistance of the material (surface) or the resistance the biofilm-modified material (bulk) is in strong need. In the Department “Materials and the Environment” of the BAM new experimental platform is being developed. With the help of different type of device for high throughput and microbiologically-controlled environment simulation we establish a new approach to clarify the mechanisms of biofilm/material interactions. Despite the focus on fundamental research, the main results of this project proposal will be transferable into material technology and construction chemistry and will influence the development of standardization in this topic. As the interactions of biofilms and materials have implications for most constructions as well as climate change, the results of the research generates additional value.
Microbially influenced corrosion (MIC) of iron is usually attributed to sulfate-reducing microorganisms (SRM) which act upon the metal by the reactiveness of hydrogen sulfide, and by withdrawal of the available electrons (Fe → Fe²⁺ + 2e⁻ ; E° = 0.47 V) in electrical contact through surface attachment. Also methanogenic archaea are supposed to cause MIC. Because they do not produce hydrogen sulfide, withdrawal of electrons may be their main corrosive mechanism; however, mechanistic details and kinetics of the overall process are poorly understood. Precipitation of siderite (4Fe + 5HCO₃⁻ + 5H⁺ → 4FeCO₃ + CH₄ + 3H₂O) can lead to an insulating layer on the metal surface and lower the corrosion rate. Still, the extent of FeCO₃ precipitation may be significantly influenced by environmental conditions such as pH and advective processes.
To investigate the corrosive potential of methanogens, we studied strains isolated from marine sediments (Methanococcus maripaludis 14266, 2067, Methanobacterium-affiliated strain IM1), crude oil tanks (Methanococcus maripaludis Mic1c10, KA1) and the oral cavity (Methanobrevibacter oralis) in a closed (batch) culture, and in a sand-packed flow-through cell with pH control and simulation of a fluctuating environment. Results indicate that the rates of iron corrosion due to coupled methanogenesis (up to 0.3 mm/yr) are comparable to that caused by SRM. Surface analyses of the metal showed severe pitting. Such knowledge and deeper understanding also from an electrokinetic point of view may not only provide further models in microbial electrophysiology, but also contribute to mitigation strategies in MIC.
Microbiologically influenced corrosion (MIC) of iron is usually attributed to sulfate-reducing microorganisms, either chemically (formation of hydrogen sulfide) or electrically (direct electron uptake). Methanogenetic Archaea are also known to be involved in iron corrosion, forming a multi-species biofilm on corroding metallic structures. However, mechanistic details and kinetics of the overall process in methanogen-induced MIC are poorly understood.
Microbiologically influence corrosion (MIC) has become a big concern due the increased usage of different metals by our society. Microorganisms can use metal as an electron donor, causing unpredictable but serious damages. Nowadays it is known that besides sulfate reducing bacteria (SRB), other microorganisms including acetogens, iron oxidizers and methanogens can also induce MIC. Current studies related to methanogen-induced MIC (MI-MIC) mainly focused on environmental isolates from the oil and gas industry (e.g. Methanococcus maripaludis) with industrial materials e.g. iron. However, MI-MIC can occur in many other environments as well, including the oral cavity. Methanobrevibacter oralis is a methanogen isolated from the human oral cavity and was found more frequently in patients suffering from peri-implantitis/periodontitis. Titanium-implants removed from those patients have also showed clear signs of corrosion. The aim of our study is to establish and analyze corrosion potentials of dental metals (e.g. titanium) by oral methanogens. Periodontal pockets samples from patients suffering from periodontitis/peri-implantitis were taken for methanogenic and SRB enrichments. Stainless steel, pure titanium or Ti-6Al-4V alloy was used for corrosion studies. Corrosion rates and methane production were measured using weight-loss method and gas chromatography, respectively. Metal surfaces were visualized with scanning electron microscopy. Microbial communities in the dental pockets of healthy people and patients will be compared using 16S rRNA amplicon sequencing. Overall, this is the first study investigating the susceptibility of different dental implant materials to corrosion using human-related Archaea. The outcomes of this study can be further explored for a variety of clinical applications.
Since the early 19th century microorganisms were studied on their capabilities of causing microbiologically influenced corrosion (MIC) of metals. The most studied ones are sulfate-reducing bacteria (SRB), but others can corrode metals as well, e.g. acid-producing bacteria or methanogenic archaea (MA). However, these studies were mostly focused on metals related to the petroleum industry but metals for other industries, e.g. dentistry, are also susceptible to corrosion. The inert Titanium (Ti) is often used as an implant material, but it is a base metal. The formation of a passivating oxide layer allows Ti to be corrosion resistant at normal conditions.
Nonetheless, scanning electron microscope images on dental implants from patients with acute peri-implantitis showed clear signs of corrosion. Currently, the corrosion mechanism of dental implants is unknown, but many indications suggest that oral microorganisms, including MA (Methanobrevibacter oralis) and SRB (Desulfomicrobium orale), could be involved.
To determine if MA or SRB can corrode Ti (pure Ti or Ti-6Al-4V alloy), corrosion rate, methane and sulfide concentrations were analyzed. Electrical potential measurements using in-house developed electrochemical cells indicated a potential change on Ti in the presence of a corrosive MA strain compared to an abiotic control.
Microbial composition comparison will be analyzed using samples from dental pockets of 150 infected patients by considering the quality of the implant and 50 healthy people by means of amplicon sequencing. Enrichments and isolation of pure cultures from the dentals samples are also examined for their corrosion behavior. Overall, this is the first study investigating the susceptibility of dental implant material to corrosion using human related MA.
Different environmental samples reveal that methanogenic Archaea are part of a
multi-species biofilm on corroding metallic structures (Fig. 1). Studies on microbial
influenced corrosion (MIC) focus mainly on sulphate reducing Bacteria (SRB),
leading to the assumption that they are exclusively responsible for metal corrosion.
In fact, methanogenic Archaea are known to be involved in metal corrosion as well
(e.g.Methanococcus maripaludis DSM 2067). In some cases SRB and methanogenic
Archaea have comparable high corrosion rates. However, the underlying
mechanisms causing corrosion are still unknown. The goal of this study is to
analyse two environmental isolates (M. maripaludis DSM 2067, M. maripaludis
KA1) and two human-related isolates (Methanobrevibacter oralis and
Methanobrevibacter smithii) for their ability to deteriorate/transform metals,
which are relevant for technical and clinical applications. Moreover, the studies will
provide essential information on the interaction mechanisms of human-related
Archaea, which are frequently found in peri-implantitis, with dental material such
as implants, crowns and bridges leading to their degradation/transformation.
Different environmental samples reveal that methanogenic Archaea are part of a multi-species biofilm on corroding metallic structures (Fig. 1). Studies on microbial influenced corrosion (MIC) focus mainly on sulphate reducing Bacteria (SRB), leading to the assumption that they are exclusively responsible for metal corrosion. In fact, methanogenic Archaea are known to be involved in metal corrosion as well (e.g. Methanococcus maripaludis DSM 2067). In some cases SRB and methanogenic Archaea have comparable high corrosion rates. However, the underlying mechanisms causing corrosion are still unknown. The goal of this study is to analyse two environmental isolates (M. maripaludis DSM 2067, M. maripaludis KA1) and two human-related isolates (Methanobrevibacter oralis and Methanobrevibacter smithii) for their ability to deteriorate/transform metals, which are relevant for technical and clinical applications. Moreover, the studies will provide essential information on the interaction mechanisms of human-related Archaea, which are frequently found in peri-implantitis, with dental material such as implants, crowns and bridges leading to their degradation/ transformation.
Methanogenic Archaea
(2017)
Different environmental samples reveal that methanogenic Archaea are part of a multi-species biofilm on corroding metallic structures. Studies on microbial influenced corrosion (MIC) focus mainly on sulphate reducing Bacteria (SRB), leading to the assumption that they are exclusively responsible for metal corrosion. In fact, methanogenic Archaea are known to be involved in metal corrosion as well (e.g. Methanococcus maripaludis DSM 2067). In some cases SRB and methanogenic Archaea have comparable high corrosion rates. However, the underlying mechanisms causing corrosion are still unknown.
The goal of this study is to develop suitable methods for analyzing two environmental isolates (M. maripaludis DSM 2067, M. maripaludis KA1) and two human-related isolates (Methanobrevibacter oralis and Methanobrevibacter smithii) for their ability to deteriorate/transform metals, which are relevant for technical and clinical applications. Moreover, the studies will provide essential information on the interaction mechanisms of human-related Archaea, which are frequently found in peri-implantitis, with dental material such as implants, crowns and bridges leading to their degradation and transformation.
Biofilm formation on materials leads to high costs in industrial processes, as well as in medical applications. This fact has stimulated interest in the development of new materials with improved surfaces to reduce bacterial colonization. Standardized tests relying on statistical evidence are indispensable to evaluate the quality and safety of these new materials. We describe here a flow chamber system for biofilm cultivation under controlled conditions with a total capacity for testing up to 32 samples in parallel. In order to quantify the surface colonization, bacterial cells were DAPI (4‘,6-diamidino-2-phenylindole)-stained and examined with epifluorescence microscopy. More than 100 images of each sample were automatically taken and the surface coverage was estimated using the free open source software g’mic, followed by a precise statistical evaluation. Overview images of all gathered pictures were generated to dissect the colonization characteristics of the selected model organism Escherichia coli W3310 on different materials (glass and implant steel). With our approach, differences in bacterial colonization on different materials can be quantified in a statistically validated manner. This reliable test procedure will support the design of improved materials for medical, industrial, and environmental (subaquatic or subaerial) applications.