Friedrich, Michael W.
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Friedrich, Michael W.
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Friedrich, Michael W.
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Friedrich, Michael
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Item type:Publication, Structure and function of microorganisms in the methanic sediments of the Helgoland mud area, North Sea, Germany(2015-10-23); ; ; The Helgoland mud area was characterized by high sedimentation rates prior to 1250 AD, most likely accounted for by the disintegration of the Helgoland Island during this period. Presumably, high amounts of terrigenous metals (e.g. Fe and Mn minerals) and organic matter were deposited as a result of the high sedimentation rates. Evident from the deposition of high amounts of organic matter and metals in the past are the shallow sulfate-methane transition zone (due to rapid organic matter-dependent electron acceptor consumption) and elevated concentrations of dissolved metals (Fe and Mn) in the methanic zone of the Helgoland mud area. Such high concentrations of dissolved Fe and Mn have been observed in other highly-depositional environments (e.g. Argentine Basin, Bothnian Sea, Aarhus Bay etc.). However, whether biotic or abiotic, the source of elevated dissolved iron in the methanic zone is still not known. Amid several hypotheses, the exact mechanisms of iron reduction in methanic zones of marine sediments are also still a matter of debate. Therefore, as a first step to understanding the potential involvement of microorganisms in iron reduction in the methanic zone in marine sediments, this work provides a 16S rRNA gene-based characterization and quantification of bacteria and archaea populations in the surface and subsurface sediments of the Helgoland mud area. In addition, this work links iron reduction in the methanic zone of the Helgoland mud area to biotic activities and suggested microbial populations which may have been involved in iron cycling therein. High and depth-wisely increasing concentrations of NH4 in pore-water measurements from subsurface sediments of many highly-depositional environments around the world suggest that organic matter degradation is still ongoing in deeper sediments. Nevertheless, molecular information about the composition and diagenetic changes of organic matter from surface to subsurface sediments are few. On this front, this doctoral work shows that the most dominant bacteria and archaea populations in the subsurface sediments of the Helgoland mud area are influenced by concentration of organic matter, thus potentially important for organic matter degradation therein. Molecular characterization of a potentially bio-available portion of sedimentary organic matter (the water-extractable fraction) in the surface and subsurface sediments, using Fourier Ion Cyclotron Resonance Mass Spectrometry, most 7 importantly reveals that while aliphatic, N-rich compounds, presumably of algal origin are preferentially degraded in the surface sediments, O-rich, aromatic compounds, most likely of terrestrial origin are utilized in deeper sediments. These results are consistent with observations in subsurface soils of peatlands suggesting similar diagenetic alterations of organic matter in marine subsurface sediments. It is a three decade-old finding that when poorly-crystalline Mn (IV) is added to marine sediments, there is a rapid formation of sulfate which is linked to biological activity. However, knowledge of the diversity of microorganisms involved in this reaction is limited. In experiments investigating the potential for chemolithotrophic Mn (IV) reduction in subsurface sediments of the Helgoland mud area, this work uncovers novel uncultured Deltaproteobacteria (tentatively named Marine Sediment Manganese-reducing Enrichment, MSME Cluster) potentially involved Mn (IV)-dependent sulfate formation in marine sediments. Overall, this work adds to the current body of knowledge on microbe-mineral or geo-microbiological interactions in marine sediments. The finding that hematite enhanced methanogenesis (by 25 48 % faster) in a year-long slurry incubations with sediments from the subsurface sediment of the Helgoland mud area also provide a basis for future studies on how (semi)conductive iron minerals such as hematite, goethite, and pyrite may mediate electron transfer between specific bacterial populations and methanogens in the Helgoland mud area.doctoral thesis608 164 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Iron oxide driven methanogenesis and methanotrophy in methanic sediments of Helgoland Mud Area, North SeaElevated dissolved iron concentrations (Fe2 ), as signpost for on-going iron oxide reduction in the methanic zone, are currently being detected in a wide range of marine environments. The various mechanisms that result in Fe2 release into porewater are a subject of intense debate amongst sediment geo-microbiologists. While abiotic cryptic sulfur cycling is suggested for some sites, biotic mechanisms potentially mediate iron reduction in many other sites, including the Helgoland Mud Area, North Sea. Iron oxide dependent anaerobic oxidation of methane (Fe-AOM) is primarily hypothesised as the biotic mechanism driving iron reduction in the methanic zone but organic matter degradation linked iron reduction could also play a role. Beyond geochemical data however, physiological evidence demonstrating that these processes occur and the microorganisms involved is rather scarce. In chapter two, a short-term radiotracer based experiment revealed that Fe-AOM is indeed feasible in the methanic zone of Helgoland Mud Area, albeit at very low rates under close to in situ conditions (0.095 A /- 0.03 nmol cm 3 d 1). Despite the low rates, these estimates represent the first demonstration of Fe-AOM in a marine environment bearing geochemical preconditions for Fe-AOM to occur in situ. Additionally in long-term incubations, various iron oxides (lepidocrocite, hematite and magnetite) stimulated Fe-AOM in sediments from the methanic zone. Especially with crystalline magnetite, ANME-2a were highly enriched after 250 days showing clearly, and for the first time, that ANME-2a are involved in Fe-AOM. Previous studies from the Helgoland Mud Area revealed that aromatic hydrocarbons are likely the preferred fermentation substrate in the methanic zone. This may have led to the strong correlations between fermentative bacteria, methanogenic archaea (which use fermentation products) and Fe2 concentrations. Chapter three investigated this possibility further, initially in sediment incubations and subsequently in highly enriched cultures. With benzoate as the only carbon substrate, enrichment efforts with crystalline iron oxides (magnetite and hematite) led to concurrent iron reduction and methanogenesis from benzoate degradation. In contrast, with poorly crystalline lepidocrocite, benzoate degradation and methanogenesis was slower. Thus, concurrent reduction of crystalline iron oxides facilitates organic matter degradation while poorly crystalline lepidocrocite inhibits the process. Therefore, a likely scenario might be in play in Helgoland Mud Area, whereby buried crystalline iron oxide phases which make up to 1.6 weight % of sediment volume could be advantageous to the microbial communities. These crystalline iron oxides likely facilitate methanogenic organic matter degradation while being reduced concurrently, thereby contributing to the Fe2 pool detected in porewater. Additionally, we uncovered the clostridial family Halobacteroidaceae as previously unknown benzoate degraders from marine sediments. In chapter four, sediment incubations with an easily fermentable substrate (glucose) revealed that crystalline iron oxides could act as conduits for electron transfer, as electron acceptors for iron reduction or act as both under various temperature regimes. Furthermore, iron reduction was more favorable under lower temperatures than at mesophilic conditions and dissimilatory iron reducers from the order Desulfuromonadales were enriched during iron reduction. These findings substantially advance the current state of the art regarding the biotic mechanisms that drive the apparent concurrent iron reduction in methanic zones of marine sediments. Besides providing direct evidence for Fe-AOM, the body of work presented in this thesis demonstrates the various ways iron oxides could facilitate methanogenic organic matter degradation in ferruginous methanic marine sediments. The exact molecular guides for these various processes should be subject of future studies.doctoral thesis456 172 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Effect of humic substances on microbial community composition and iron reduction in marine sedimentsHumic substances (HS) are a complexed mixture of organic compounds formed from decomposition of organic matter. They are known to play a role in anaerobic respiration as extracellular electron shuttling molecules. This is due to their unique molecular structure that contains quinone moieties as the redox active sites. HS are known to be biotically reduced, and in turn donate abiotically their electrons to iron oxides. Most iron reducing bacteria were found to be able to reduce HS, but also other microorganisms, such as methanogens and fermenters, are able to do so. Therefore, there is a high potential for their impact on the iron cycle. Although the impact of humics on populations and kinetics of iron reduction were shown before in soils and fresh water sediments, little is known about their impact in marine sediments. In this thesis, I investigated the effect of the humic analog 9,10-anthraquinone-2,6- disulfonate (AQDS) on microbial populations and iron reduction in marine surface sediments. Three marine sites were studied: (1) The Wadden Sea tidal flats (Dorum-Neufeld), (2) the Helgoland mud area (North Sea), and (3) the shallow hydrothermal vent systems at the island of Dominica (Lesser Antilles). Anoxic sediment incubations were performed and iron reduction rates were determined. For investigating the microbial community, which is involved in humic and iron respiration, I used different methods. Microbial ribosomal RNA (rRNA) gene community fingerprints were analyzed by terminal restriction fragment length polymorphism (TRFLP). For quantification I used most probable number (MPN) incubations. For identification of the active population, which can assimilate acetate (13C-labeled) and couple it to iron and humic reduction, stable isotope probing of RNA (RNA-SIP) was used. Iron reduction was significantly stimulated by addition of AQDS. The stimulation resulted in up to ~ 4.5 times more Fe2 formed than in control incubations. Furthermore, low AQDS concentrations such as 0.5 and 5 µM resulted in higher stimulation of iron reduction than using 50 and 1000 µM. These results suggest that iron reduction was limited by the availability of quinone moieties in slurry incubations. In incubations with sediment from Wadden Sea and North Sea, iron reduction was stimulated as a result of acetate addition, suggesting that availability of electron donors for iron reduction was also limiting. When using sediment from Dominica hydrothermal vents, no stimulation was observed. Quantification of AQDS-reducing microorganisms by most probable number cultivation resulted in ~ 50 times higher numbers than with iron oxide as sole electron acceptor. Additionally, differences in microbial community fingerprinting structure were observed. When using sediment from Dorum or Helgoland, community structure was affected mainly by electron donor amendment. In contrast, in incubations from Dominica, microbial community structure was affected by AQDS amendment, suggesting that quinone respiration is a more common property in Wadden Sea and North Sea sediments. Using RNA-SIP approach, I showed that Desulfuromonadales spp. are the main microorganisms who could couple acetate assimilation to AQDS and iron reduction in sediments from Dorum and Helgoland, implying that humic respiration coupled to acetate oxidation is carried out by iron reducing bacteria. In incubations with sediment from Dominica when AQDS was amended the Halobacteriales group DHVEG-6 was found as main acetate assimilating microorganism. This result gives direct evidence for the ability of an uncultivated archaeal group to utilize acetate with AQDS. Overall, the results presented in this thesis provide insight to the barely studied field of the in-situ utilization of HS in marine sediments. They suggest that there is a high potential to use HS for respiration in marine sediments. Therefore, input of organic carbon in the form of HS will likely result in a stimulation of carbon mineralization and enhance iron reduction through electron shuttling in marine sediments.doctoral thesis407 257 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, (Acido)bacterial diversity in space and timeRecent technological achievements enabled microbiologists to fully grasp the vast diversity of microbial life that is resident in soils, highly complex matrices of alternating micro-habitats on very small scales. Since then, microbial community composition has been catalogued for many different terrestrial habitats. This triggered the investigation and definition of processes which shape these communities. In most cases, the environment determines community composition, and similar habitats may feature similar microbial communities despite being far apart. However, some habitats have been described as subjected to pronounced neutral processes, which are dispersal, ecological drift or speciation. The balance between these process types is now the subject of many studies looking at microbial communities. It is also clear that these processes need to be monitored on both temporal and spatial scales, as the two dimensions are inseparably interlinked. However, most microbial studies deal with only one aspect, but do not control for the other. In this work, the outcome of a highly sophisticated plot scale experiment is presented encompassing 358 sampling locations distributed between six intra-annual sampling points on a 10 m x 10 m unfertilized grassland site in the Swabian Alb. RNA was extracted from the A-horizon of each soil and the hypervariable region 3 of the ribosomal small subunit was amplified and sequenced with barcoded Illumina sequencing. Roughly 400 million eubacterial reads were obtained. The dataset was used to assess the population dynamics of Acidobacteria, as well as the spatio-temporal co-occurenze of functionally depending microorganism. Additionally, preliminary results motivated the assessment of common methods for the examination of rhizospheric communities. In combination, the diversity of bacterial communities in space and time was tested from different angles, reflecting different research question, and they all revealed a far more complex reality than previously thought.doctoral thesis358 299 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Phylogenetische und funktionelle Diversität von Acidobacteria in Wald- und Grünlandböden unterschiedlicher LandnutzungThe identification of edaphic and biotic parameters influencing diversity and activity of Acidobacteria is a prerequisite to understand their role in soil biogeochemical cycles. Here, Acidobacteria diversity changes in grassland and forest soils of different landuse were assessed by sequencing and community fingerprints (T-RFLP) of 16S rRNA. Differences in Acidobacteria community composition were found between the study regions in Germany, between grassland and forest as well as between soil types and apart from soil moisture, carbon, nitrogen, ammonium and phosphorus content, Acidobacteria were predominantly influenced by soil pH. Furthermore, the diversity of Acidobacteria differed seasonally with highest diversity in October. Stable isotope probing was performed to follow the degradation of wheat residues in microcosms of a grassland and forest soil and to identify the bacteria involved by T-RFLP analysis and (pyro)sequencing of 16S rRNA. The wheat residue degrading microbial community was dominated by members of Actinobacteridae, α- and β-Proteobacteria, whereas Acidobacteria did not play a role in early degradation of plant residues.doctoral thesis325 129 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Carbon cycling in (sub-) Antarctic marine anoxic sediments(2025-02-13); ; ; Im marinen Sediment stellt die anaerobe Zersetzung organischen Kohlenstoffs durch eine mikrobielle Gemeinschaft einen wichtigen Teil des globalen Kohlenstoffzyklus dar. Die Folgen der globalen Erwärmung sind in den marinen Sedimenten der polaren Regionen bereits jetzt deutlich wahrnehmbar. Die Temperatur steigt und beschleunigtes Abschmelzen der Gletscher führt durch Gletscherschmelzwasser zu einem erhöhten Eintrag von Nährstoffen wie Metalloxiden in die Sedimente. Da diese Metalloxide als terminale Elektronenakzeptoren für anaeroben organischen Kohlenstoffabbau dienen können, wird ein Einfluss der beschriebenen Änderungen auf jene Prozesse und die assoziierten Mikroorganismen vorausgesagt. Änderungen können allerdings nur sinnvoll vorausgesagt werden, wenn der aktuelle Status des untersuchten Systems verstanden wurde und insbesondere marine Sedimente in der Antarktis sind bisher kaum untersucht worden. Die Sedimente der in dieser Dissertation untersuchten Gebiete, Potter Cove auf der König- Georg-Insel/Isla 25 de Mayo an der Westantarktischen Halbinsel und Südgeorgien im Südatlantik, werden stark durch schmelzende Gletscher beeinflusst. Ich habe die mikrobielle Gemeinschaft und Geochemie in situ untersucht, fokussiert auf den finalen Kohlenstoffabbau. Zusätzlich habe ich in simplen Inkubationsexperimenten und Inkubationen mit stabiler Isotopenbeprobung (stable isotope probing: SIP) auf RNA-Level die acetatabbauenden Mikroorganismen untersucht und Eisenoxide, Manganoxide und Sulfat als terminale Elektronenakzeptoren getestet. Eisenoxide und, wenn zugesetzt, auch Manganoxide, dienten als Elektronenakzeptoren für die Acetatoxidierung. Der hauptsächlich verantwortliche Mikroorganismus für die Eisenreduktion in allen untersuchten Sedimenten war der unkultivierte Sva1033 (Desulfuromonadales). Dies ist der erste experimentelle Nachweis für eine Stoffwechselfähigkeit dieser kaum untersuchten Gruppe. Da Sva1033 der dominante eisenreduzierende Mikroorganismus in situ und in RNA-SIP Inkubationen, sogar bei höheren Temperaturen, war, konnte ich ihn als Schlüsselart für Acetatoxidation in den untersuchten Umgebungen identifizieren. Des Weiteren konnte durch acetatabbauende SIP Experimente eine mikrobielle Gemeinschaft gezeigt werden, die über einen weiten Temperaturgradienten aktiv war, zum Beispiel die Mikroorganismen Sva1033 und Desulfuromonas. Andere Mikroorganismen waren nur bei bestimmten Temperaturen aktiv, zum Beispiel Arcobacteraceae bei niedrigen und Desulfuromusa bei hohen Temperaturen. Desulfuromusa war zusätzlich der dominierende Mikroorganismus, der bei niedriger in situ Temperatur Manganoxide reduziert und Acetat oxidiert hat. Trotz ihrer hohen Abundanz in den in situ Sedimenten, schienen sulfatreduzierende Mikroorganismen in all den durchgeführten Experimenten nicht zur Acetatoxidation beizutragen, waren allerdings in mehreren SIP Experimenten im Hintergrund vorhanden. Des Weiteren konnten SIP Experimente keinen autotrophischen Lebensstil der Sulfatreduzierer zeigen, obwohl Sulfatreduktion durch Acetat- und Wasserstoffzugabe stimuliert werden konnte. Auch die durch Sulfatreduzierer verwendeten Elektronendonoren bleiben schwer zu fassen und weitere Untersuchungen sind notwendig. Stattdessen wurde ein potentiell neuer Bakterienstamm von Sulfurimonas in SIP Experimenten mit den höchsten Sulfatreduktionsraten identifiziert, welcher einen anaeroben, psychrophilen Lebensstil vollführt und Acetat und CO2 assimiliert hat. Ich schlage Sulfid als genutzten Elektronendonor und Syntrophie mit einem anderen Mikroorganismus als elektronenakzeptierenden Partner vor, allerdings werden weitere Experimente benötigt um diese Hypothesen zu bestätigen und weiteres Licht auf den durch den Mikroorganismus durchgeführten Metabolismus zu werfen. Durch Beschreibungen und vorausgesagte Stoffwechselaktivitäten der mikrobiellen Gemeinschaft in gletscherbeeinflussten, marinen Sedimenten der Antarktis tragen die Untersuchungsergebnisse dieser Dissertation zum Forschungsfeld der anaeroben Mikroorganismen in marinen Sedimenten bei. Aufgrund meiner Forschungsergebnisse halte ich es für wahrscheinlich, dass die organische Materialien zersetzende mikrobielle Gemeinschaft stark durch vom Gletscherschmelzwasser eingetragene Nährstoffe beeinflusst wird und dadurch höchst sensibel auf zukünftige Änderungen in dieser durch globale Erwärmung beeinflussten Umwelt reagieren könnte.doctoral thesis117 93 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Microbial community functioning at hypoxic sediments revealed by targeted metagenomics and RNA stable isotope probingMicroorganisms are instrumental to the structure and functioning of marine ecosystems and to the chemistry of the ocean due to their essential part in the cycling of the elements and in the recycling of the organic matter. Two of the most critical ocean biogeochemical cycles are those of nitrogen and sulfur, since they can influence the synthesis of nucleic acids and proteins, primary productivity and microbial community structure. Oxygen concentration in marine environments is one of the environmental variables that have been largely affected by anthropogenic activities; its decline induces hypoxic events which affect benthic organisms and fisheries. Hypoxia has been traditionally defined based on the level of oxygen below which most animal life cannot be sustained. Hypoxic conditions impact microbial composition and activity since anaerobic reactions and pathways are favoured, at the expense of the aerobic ones. Naturally occurring hypoxia can be found in areas where water circulation is restricted, such as coastal lagoons, and in areas where oxygen-depleted water is driven into the continental shelf, i.e. coastal upwelling regions. Coastal lagoons are highly dynamic aquatic systems, particularly vulnerable to human activities and susceptible to changes induced by natural events. For the purpose of this PhD project, the lagoonal complex of Amvrakikos Gulf, one of the largest semi-enclosed gulfs in the Mediterranean Sea, was chosen as a study site. Coastal upwelling regions are another type of environment limited in oxygen, where also formation of oxygen minimum zones (OMZs) has been reported. Sediment in upwelling regions is rich in organic matter and bottom water is often depleted of oxygen because of intense heterotrophic respiration. For the purpose of this PhD project, the chosen coastal upwelling system was the Benguela system off Namibia, situated along the coast of south western Africa. The aim of this PhD project was to study the microbial community assemblages of hypoxic ecosystems and to identify a potential link between their identity and function, with a particular emphasis on the microorganisms involved in the nitrogen and sulfur cycles. The methodology that was applied included targeted metagenomics and RNA stable isotope probing (SIP). It has been shown that the microbial community diversity pattern can be differentiated based on habitat type, i.e. between riverine, lagoonal and marine environments. Moreover, the studied habitats were functionally distinctive. Apart from salinity, which was the abiotic variable best correlated with the microbial community pattern, oxygen concentration was highly correlated with the predicted metabolic pattern of the microbial communities. In addition, when the total number of Operational Taxonomic Units (OTUs) was taken into consideration, a negative linear relationship with salinity was identified (see Chapter 2). Microbial community diversity patterns can also be differentiated based on the lagoon under study since each lagoon hosts a different sulfate-reducing microbial (SRM) community, again highly correlated with salinity. Moreover, the majority of environmental terms that characterized the SRM communities were classified to the marine biome, but terms belonging to the freshwater or brackish biomes were also found in stations were a freshwater effect was more evident (see Chapter 3). Taxonomic groups that were expected to be thriving in the sediments of the Benguela coastal upwelling system were absent or present but in very low abundances. Epsilonproteobacteria dominated the anaerobic assimilation of acetate as confirmed by their isotopic enrichment in the SIP experiments. Enhancement of known sulfate-reducers was not achieved under sulfate addition, possibly due to competition for electron donors among nitrate-reducers and sulfate-reducers, to the inability of certain sulfate-reducing bacteria to use acetate as electron donor or to the short duration of the incubations (see Chapter 4). Future research should focus more on the community functioning of such habitats; an increased understanding of the biogeochemical cycles that characterize these hypoxic ecosystems will perhaps allow for predictions regarding the intensity and direction of the cycling of elements, especially of nitrogen and sulfur given their biological importance. Regulation of hypoxic episodes will aid the end-users of these ecosystems to possibly achieve higher productivity, in terms of fish catches, which otherwise is largely compromised by the elevated hydrogen sulfide concentrations.doctoral thesis387 482 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Degradation of marine and terrestrial organic matter in anoxic marine sediments of the Helgoland mud area(2025-03-07); ; ; ; Große Mengen organischen Kohlenstoffs marinen und terrestrischen Ursprungs sind in marinen Sedimenten abgelagert. Mikroorganismen, die diese Sedimente bewohnen, remineralisieren organischen Kohlenstoff, in dem sie große komplexe Moleküle in kleinere organische Moleküle und schließlich inorganischen Kohlenstoff abbauen. Der Prozess der Remineralisierung wird durch eine komplexe Gemeinschaft bestehend aus primären Fermentern, die große komplexe organische Stoffe nutzen, sekundären Fermentern, die Fermentationsprodukte nutzen und respiratorischen Organismen, die die Oxidation der Fermentationsprodukte mit der Reduktion von Elektronenakzeptoren koppeln, durchgeführt. Trotz der bestehenden Forschung sind viele Bakterien und Archaeen, die in der Remineralisierung von organischen Materialien involviert sind, aufgrund fehlender Isolation weitestgehend nicht charakterisiert. Während neue Daten integrierenden Studien versuchen mehr Licht in die phylogenetische Diversität zu bringen, konnten bisher nur wenige der Mikroorganismen charakterisiert werden. Diese Dissertation hat das Ziel Bakterien und Archaeen, die organischen Kohlenstoff remineralisieren, zu charakterisieren und komplexe mikrobielle Interaktionen aufzudecken. Dabei wird eine Kombination aus Anreicherungen, dem Beproben stabiler Isotope (SIP), Metagenomanalysen und der Sammlung und Analyse von weiteren Daten angewendet. In Kapitel II beschreibe ich die Anwendung eines neu entwickelten SIP, das mit kleinen Sedimentmengen durchgeführt wurde und 18O als Substrat nutzt, um aktive Mikroorganismen in situ zu detektieren. Dabei wurden Mitglieder der Klasse Desulfobulbia als dominante Organismen entdeckt, die im finalen Schritt des Abbaus organischen Materials involviert sind. Aktive heterotrophe sekundäre Fermenter, wie die Fusobacteriia, Clostridia und Bacteroidia und respiratorische Organismen wie Sva1033 wurden im Sediment entdeckt und mit Fermentationsprodukten von anderen Taxa versorgt, die im Abbau von komplexen organischen Materialien beteiligt waren. Als solche wurde, zum Beispiel eine unbeschriebene Klasse innerhalb der Thermoplasmatota entdeckt, die im Abbau von Proteinen involviert ist (Kapitel III). Die Repräsentation der EX4484-6 Klasse war bisher auf fünf Genome aus einer Ordnung beschränkt und konnte durch unsere Entwicklung einer Methode zur Datensuche und -analyse verbessert werden. Hierdurch wird die Klasse nun durch drei neue Ordnungen ergänzt. Aufgrund der geringen Abundanz dieser Gruppe in globalen küstennahen marinen Sedimenten, konnten wir die EX4484-6 Klasse der seltenen Biosphäre zuordnen. Durch funktionelle Vergleiche der Mitglieder mit anderen Thermoplasmatota, haben wir neue Funktionalität innerhalb der neuen Klasse entdeckt, die sich durch eine hohe Zahl an unklassifizierten Genen auszeichnet, die nicht in anderen Mitgliedern der Thermoplasmatota auftreten. Andere aktive primäre Fermenter waren unbeschriebene Mitglieder aus vier Ordnungen der Clostridia, die methoxylierte aromatische Verbindungen (MACs) terrestrischen Ursprungs nutzen (Kapitel IV). Diese Clostridia konnten eine große Vielfalt an verschiedenen MACs nutzen. Das metabolische Potential zeigte jedoch auch ein generelles Potential für die Nutzung andere C1-Kohlenstoffe auf und indiziert damit, dass diese Organismen auch anderen Kohlenstoff in marinen Sedimenten transformieren können. Die Ergebnisse, die in dieser Dissertation präsentiert werden, geben einen neuen Einblick in zuvor unentdeckte Mikroorganismen, die in der Remineralisierung von organischen Materialien in marinen Sedimenten involviert sind. Dabei wurden nicht nur abundante Organismen, sondern auch Organismen der seltenen Biosphäre entdeckt, die zur Remineralisierung der organischen Kohlenstoffverbindungen beitragen. Damit zeigt diese Dissertation, dass auch wenig abundante Taxa in marinen Sedimenten wichtig für den Abbau organischen Kohlenstoffs sein können. Das Auffinden von diversen kaum untersuchten Mikroorganismen und ihres neuen funktionellen Potentials deutet auf die enorme mikrobielle Diversität hin, die noch immer darauf wartet, entdeckt zu werden.doctoral thesis127 120