Physiology of a marine Beggiatoa strain and the accompanying organism Pseudovibrio sp. - a facultatively oligotrophic bacterium

Large filamentous sulfide-oxidizing bacteria are capable of forming huge microbial mats at the oxic-anoxic interface of the sediment surface. The first part of this thesis shows that a subpopulation of Beggiatoa filaments actively migrates into anoxic, sulfidic layers as a reaction to high sulfide fluxes. The reason for this so far unknown migration behavior seems to be excessive storage of reserve compounds. By moving into anoxic regions, aerobic sulfide oxidation is stopped and storage space is emptied by reducing the stored sulfur with carbon reserve compounds. The association of the sulfide-oxidizer and a small heterotrophic bacterium (Pseudovibrio sp.) is investigated in the second part of this thesis. In contrast to the large Beggiatoa sp., the Pseudovibrio sp. is able to grow in pure culture under extremely oligotrophic conditions. Under oligotrophic conditions we found that Pseudovibrio sp. grows on organic contaminations preferentially containing nitrogen

Sulfur Respiration in a Marine Chemolithoautotrophic Beggiatoa Strain

The chemolithoautotrophic strain Beggiatoa sp. 35Flor shows an unusual migration behavior when cultivated in a gradient medium under high sulfide fluxes. As common for Beggiatoa spp., the filaments form a mat at the oxygen–sulfide interface. However, upon prolonged incubation, a subpopulation migrates actively downward into the anoxic and sulfidic section of the medium, where the filaments become gradually depleted in their sulfur and polyhydroxyalkanoates (PHA) inclusions. This depletion is correlated with the production of hydrogen sulfide. The sulfur- and PHA-depleted filaments return to the oxygen–sulfide interface, where they switch back to depositing sulfur and PHA by aerobic sulfide oxidation. Based on these observations we conclude that internally stored elemental sulfur is respired at the expense of stored PHA under anoxic conditions. Until now, nitrate has always been assumed to be the alternative electron acceptor in chemolithoautotrophic Beggiatoa spp. under anoxic conditions. As the medium and the filaments were free of oxidized nitrogen compounds we can exclude this metabolism. Furthermore, sulfur respiration with PHA under anoxic conditions has so far only been described for heterotrophic Beggiatoa spp., but our medium did not contain accessible organic carbon. Hence the PHA inclusions must originate from atmospheric CO2 fixed by the filaments while at the oxygen–sulfide interface. We propose that the directed migration of filaments into the anoxic section of an oxygen–sulfide gradient system is used as a last resort to preserve cell integrity, which would otherwise be compromised by excessive sulfur deposition occurring in the presence of oxygen and high sulfide fluxes. The regulating mechanism of this migration is still unknown

Physiologie von einem marinen Beggiatoa Stamm und dem Begleitorganismus Pseudovibrio sp. - ein fakultativ oligotrophes Bakterium

Large filamentous sulfide-oxidizing bacteria are capable of forming huge microbial mats at the oxic-anoxic interface of the sediment surface. The first part of this thesis shows that a subpopulation of Beggiatoa filaments actively migrates into anoxic, sulfidic layers as a reaction to high sulfide fluxes. The reason for this so far unknown migration behavior seems to be excessive storage of reserve compounds. By moving into anoxic regions, aerobic sulfide oxidation is stopped and storage space is emptied by reducing the stored sulfur with carbon reserve compounds. The association of the sulfide-oxidizer and a small heterotrophic bacterium (Pseudovibrio sp.) is investigated in the second part of this thesis. In contrast to the large Beggiatoa sp., the Pseudovibrio sp. is able to grow in pure culture under extremely oligotrophic conditions. Under oligotrophic conditions we found that Pseudovibrio sp. grows on organic contaminations preferentially containing nitrogen

Molecular characterization of selected pathogen-responsive receptor kinases from Arabidopsis thaliana

Pflanzen verfügen über verschiedene Arten von Rezeptoren um die Gegenwart potentieller Pathogene zu perzipieren. Eine der größten Genfamilien unter ihnen stellt, nach Arabidopsis-Genomanalyse, die Gruppe der leuzinreichen Rezeptorkinasen (LRR-RLKs) dar. Neben der Funktion von LRR-RLKs in pflanzlichen Entwicklungsprozessen konnte bisher nur für die PAMP-Rezeptoren FLS2 und EFR eine Aufgabe in der Pathogenabwehr nachgewiesen werden. Unter Zuhilfenahme der reversen Genetik war es in dieser Arbeit möglich für drei Kandidaten die Bedeutung in Prozessen der angeborenen Immunität nachzuweisen. Die DRK5 ist scheinbar an der Vermittlung der Basisresistenz nach Pto DC3000-Infektion beteiligt. Die Überprüfung des bakteriellen Wachstums in drk5-Mutanten zeigt eine erhöhte Suszeptibilität der Pflanzen gegenüber diesem Pathogen verglichen mit dem Wildtyp. Nichtvirulente und avirulente Bakterien weisen jedoch kein verändertes Wachstum auf. Für die DRK6 war es möglich, eine Beteiligung in der kultivarspezifischen Immunantwort nachzuweisen. Ein DRK6-Gendefekt hat dabei spezifisch Einfluss auf die vollständige Etablierung der RPM1-vermittelten Resistenz. Er erhöht die Suszeptibilität der Pflanze gegenüber Pto AvrRpm1 und Pto avrB, nicht jedoch gegenüber Pto avrRpt2. Für die Rezeptorkinase BAK1 wurde in früheren Experimenten gezeigt, dass sie je nach Interaktionspartner in verschiedenen Prozessen involviert sein kann. Einerseits ist sie als BRI1-Korezeptor an der Brassinolidperzeption beteiligt, andererseits ist sie als Interaktionspartner von PAMP-Rezeptoren in der Lage, brassinolidunabhängig in die Pathogenabwehr einzugreifen. BAK1-gendefiziente Pflanzen weisen zusätzlich eine unkontrollierte Ausbreitung von Zelltod nach Infektion mit Pathogenen auf, welche unabhängig von Brassinolid- und Flagellinperzeption ist. Es wird vermutet, dass BAK1 als Korezeptor oder Regulator verschiedener Rezeptoren Einfluss auf unterschiedliche pflanzliche Prozesse nimmt.With the help of various receptors plants are able to percept the presence of potential pathogens. According to Arabidopsis genome analysis one of the largest gene families among these is the group of leucin-rich receptor-like kinases (LRR-RLKs). Beside the function of LRR-RLKs in plant development only for the PAMP receptors FLS2 and EFR one could demonstrate their role in pathogen defence. In a reverse genetic approach it was possible to confirm the role in processes of innate immunity for three further candidates in this work. DRK5 seems to mediate basal resistance upon Pto DC3000 infection. Examination of the bacterial growth in drk5 mutants reveals enhanced susceptibility of these plants in comparision to wildtyp plants. Nonvirulent and avirulent bacteria do not show altered growth. For DRK6 it was possible to show its participation in cultivar specific immunity. A DRK6-gene defect influences the proper establishment of RPM1-mediated resistance. It enhances the susceptibility against Pto avrRpm1 and Pto avrB, but not against Pto avrRpt2. In previous experiments the receptor kinase BAK1 was shown to be involved in different processes depending on its interaction partner. On the on hand it takes part in Brassinolid perception as coreceptor of BRI1. On the other hand it is able to influence pathogen defence in a Brassinolid independent manner as interaction partner of PAMP receptors. BAK1-deficient plants show uncontrolled spreading cell death independent of brassinolid or flagellin perception. Thus BAK1 is supposed to influence independent processes as coreceptor or regulator of different receptors

Changes of dissolved organic matter compositions in artifical and natural seawater during Pseudovibrio growth experiment

Marine planktonic bacteria often live in habitats with extremely low concentrations of dissolved organic matter (DOM). To study the use of trace amounts of DOM by the facultatively oligotrophic Pseudovibrio sp. FO-BEG1, we investigated the composition of artificial and natural seawater before and after growth. We determined the concentrations of dissolved organic carbon (DOC), total dissolved nitrogen (TDN), free and hydrolysable amino acids, and the molecular composition of DOM by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR-MS). The DOC concentration of the artificial seawater we used for cultivation was 4.4 µmol C/l, which was eight times lower compared to the natural oligotrophic seawater we used for parallel experiments (36 µmol C/l). During the three-week duration of the experiment, cell numbers increased from 40 cells/ml to 2x10**4 cells/ml in artificial and to 3x10**5 cells/ml in natural seawater. No nitrogen fixation and minor CO2 fixation (< 1% of cellular carbon) was observed. Our data show that in both media, amino acids were not the main substrate for growth. Instead, FT-ICR-MS analysis revealed usage of a variety of different dissolved organic molecules, belonging to a wide range of chemical compound groups, also containing nitrogen. The present study shows that marine heterotrophic bacteria are able to proliferate with even lower DOC concentrations than available in natural ultra-oligotrophic seawater, using unexpected organic compounds to fuel their energy, carbon and nitrogen requirements

Substrate Use of <i>Pseudovibrio</i> sp. Growing in Ultra-Oligotrophic Seawater

<div><p>Marine planktonic bacteria often live in habitats with extremely low concentrations of dissolved organic matter (DOM). To study the use of trace amounts of DOM by the facultatively oligotrophic <i>Pseudovibrio</i> sp. FO-BEG1, we investigated the composition of artificial and natural seawater before and after growth. We determined the concentrations of dissolved organic carbon (DOC), total dissolved nitrogen (TDN), free and hydrolysable amino acids, and the molecular composition of DOM by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR-MS). The DOC concentration of the artificial seawater we used for cultivation was 4.4 μmol C L^-1, which was eight times lower compared to the natural oligotrophic seawater we used for parallel experiments (36 μmol C L ^-1). During the three-week duration of the experiment, cell numbers increased from 40 cells mL^-1 to 2x10⁴ cells mL ^-1 in artificial and to 3x10⁵ cells mL ^-1 in natural seawater. No nitrogen fixation and minor CO₂ fixation (< 1% of cellular carbon) was observed. Our data show that in both media, amino acids were not the main substrate for growth. Instead, FT-ICR-MS analysis revealed usage of a variety of different dissolved organic molecules, belonging to a wide range of chemical compound groups, also containing nitrogen. The present study shows that marine heterotrophic bacteria are able to proliferate with even lower DOC concentrations than available in natural ultra-oligotrophic seawater, using unexpected organic compounds to fuel their energy, carbon and nitrogen requirements.</p></div

Summary of FT-ICR-MS results: Numbers of assigned formulas, significantly (p < 0.05) changing and decreasing peaks (N-containing compounds were subset of the overall decreasing compounds) in artificial and natural seawater.

<p>Summary of FT-ICR-MS results: Numbers of assigned formulas, significantly (p < 0.05) changing and decreasing peaks (N-containing compounds were subset of the overall decreasing compounds) in artificial and natural seawater.</p

Purified artificial seawater (medium 3; AS) and natural seawater (NS): Concentrations of dissolved organic carbon (DOC), total dissolved nitrogen (TDN), dissolved free amino acids (DFAA), dissolved combined amino acids (DCAA) and total hydrolysable dissolved amino acids (THDAA) at the different time points: before bottling: only medium; blank: medium poured into serum bottles before inoculation; t₀: directly after inoculation; t₁: 1 week after inoculation; t₂: 3 weeks after inoculation.

<p>(n.d. = not determined).</p

Cell numbers in the different media after 1 and 3 weeks of incubation (initial cell number after inoculation was calculated to be ca. 40 cells mL^-1).

<p>Parallel uninoculated controls were checked for all different media and no cells were observed. (n.d. = not determined; amm. = ammonium; gluc. = glucose)</p><p>Cell numbers in the different media after 1 and 3 weeks of incubation (initial cell number after inoculation was calculated to be ca. 40 cells mL^-1).</p