Wichels, Antje
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Wichels, Antje
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Wichels, Antje
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Wichels, A.
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Item-typ:Veröffentlichung, Diversity and function of phages modulating North Sea bacteria(2020-10-05); ; ; The investigation of phages, their diversity, and their modulating role of bacterial populations during spring blooms in the North Sea was the major goal of this thesis. The research was conducted close to the island of Helgoland, in the German Bight, at the long-term ecological research station Kabeltonne. While factors inducing phytoplankton blooms and succeeding bacterioplankton blooms are intensively studied and fairly well understood, the mortality factors responsible for the subsequent decrease in microbial abundance are not yet well explored. To explore the relevance of phage lysis as a mortality factor modulating the bacterial population, lytic phages were isolated from the coastal waters off Helgoland during the spring phytoplankton blooms of two subsequent years. Most bacterial host strains were selected from bacterial taxa previously identified to be abundant in spring blooms. Phages infecting Flavobacteriia were the focus of this thesis, because their hosts degrade high molecular weight substrates and are thus central catalysts of algal biomass remineralization. Phages were enriched by enrichment cultures and tangential flow filtration, and subsequently characterized by transmission electron microscopy, and comparative genome sequence analysis. In total, seventeen new phage species were isolated, including phages for the three major bacterial classes responding to phytoplankton blooms, Flavobacteriia, Alphaproteobacteria, and Gammaproteobacteria. The new species were grouped into thirteen new phage genera, belonging to eleven new families in three realms. For the official acceptance of this classification taxonomic proposals have been formulated in this thesis, which will be evaluated by the International Committee on Taxonomy of Viruses (ICTV). Overall, the huge phage diversity down to the strain level, the detection of active infections, and the phage recurrence, together suggest that phages are highly relevant mortality factors of heterotrophic bacteria during spring phytoplankton blooms.Dissertation346 252 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Diversity and abundance of Gammaproteobacteria during the winter-spring transition at station Kabeltonne - Helgoland(2011-10-19); ; ; Recent evidence has suggested that Gammaproteobacteria are strongly associated with phytoplankton blooms and may play a role in the processing of the algal derived organic substrate. Therefore, the succession of specific groups within the Gammaproteobacteria may be strongly influenced by the availability of this organic matter. Other factors such as the increase of temperature during the winter-spring transition time may also be important for such a succession as it promotes the bacterial growth rate. The aim of this thesis was to study the population dynamics of the gammaproteobacterial groups caused by a massive spring algal bloom in the North Sea. Accordingly, surface seawater was investigated, that had been taken twice weekly in years 2009 and 2010 from the long-term ecological research station Kabeltonne located at the Helgoland Roads. Bacterial diversity was examined in samples of 11.02.2009 (winter) and 14.04.2010 (spring) by comparative sequence analysis of two full-length 16S rRNA gene clone libraries. Around 800 sequences were obtained from each library and revealed that Bacteroidetes and Gammaproteobacteria comprised the major fraction of the bacterial community in the coastal North Sea in April in contrast to February when Alphaproteobacteria was retrieved in high frequency. Within the Gammproteobacteria the SAR86 clade dominated the community in the winter library while the SAR92 clade was the dominating group in the spring one. Reinekea, Balneatrix-related clade and Galciecola were genera only occurring in the spring library. For the newly occurring gammaproteobacterial groups oligonucleotide probes were designed. The full sequences of both winter and spring clone libraries were used for the in silico validation of the probe specificities. Subsequently, the abundances of the gammaproteobacterial subgroups were monitored for the years 2009 and 2010 using catalyzed reporter deposition-fluorescence in situ hybridization (CARD-FISH) and a probe set consisting of the newly designed probes and previously designed ones. The sum of all counts as detected by this set of probe covered almost 100% of cells detected by the general probe GAM42a. In the year 2009, a tight succession of members of the genera Reinekea, the SAR92, OM182 and NOR5/OM60 clades, Balneatrix-related clade, Vibrio, Glaciecola and Pseudoalteromonas was observed about one month after a discrete spring algal bloom in late March which mainly consisted of diatoms. These groups seem to respond to the substrate generated by the bloom (bottom-up effect). A succession of Reinekea spp. was observed reaching up to 140000 cells/ml. This was followed by a particular succession of SAR92 clade showing the strongest increase within the Gammaproteobacteria, up to total abundances of 300000 cells/ml. OM182 and NOR5/OM60 clades subsequently reached total abundances of 120000 cells/ml and 90000 cells/ml, respectively. These larger groups likely play a major role in the degradation of the organic matter produced by the diatoms spring bloom. Although the abundance of other gammaproteobacterial groups such as Balneatrix-related clade, Glaciecola, Vibrio and Pseudoalteromans remained lower, they also participated into the upshift with maximum abundances of 36000 cells/ml, 10000 cells/ml, 30000 cells/ml and 9000 cells/ml respectively. Members of the SAR86 clade were no major players in the succession directly after the bloom, yet, they dominated later in May reaching up to 200000 cells/ml. In year 2010, a similar succession pattern was observed for the so far investigated groups Reinekea, SAR92, SAR86 and OM182 clades, Balneatrix-related clade and Glaciecola also within one month after the phytoplankton blooming peak. This indicates that this is an annual phenomenon occurring in the North Sea during the winter-spring transition period and further suggests substrate specialization for those groups.Dissertation264 145 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Spatial resolution of aquatic fungal communities driven by the interplay of environmental factors and ecological processes(2022-12-12); ; ; Aquatische Pilze sind eine weit verbreitete Organismengruppe und sie nehmen Schlüsselrollen in wichtigen ökologischen Prozessen wie zum Beispiel dem Nährstoffkreislauf ein. Aufgrund ihrer evolutiven Entwicklung im aquatischen Bereich sowie sekundäre Besiedlungsschritte mariner Systeme verfügen sie über diverse ökologisch interessante Eigenschaften. Allerdings ist nur wenig über das Zusammenspiel von Diversität und Struktur aquatischer Pilzgemeinschaften und den beeinflussenden Faktoren bekannt. Vor allem ist die räumliche Auflösung aquatischer Pilzgemeinschaften kaum erforscht. Als Konsequenz wurden bisher Pilze kaum beachtet, wodurch die Entwicklung eines holistischen Bildes aquatischer ökologischer Prozesse gehemmt ist. Ziel meiner Dissertation war es daher, zu verstehen, wie aquatische Pilzgemeinschaften in (i) Flüssen und angrenzender Küstenzone und (ii) benthischen Systemen durch die Interaktion ökologischer Prozesse oder einzelner bis mehrerer Umweltfaktoren räumlich aufgelöst werden. In meiner Doktorarbeit habe ich die mykopelagischen und mykobenthischen Gesellschaftsstrukturen mit tag-Sequenzierung aufgelöst (18S rDNA Gensequenz oder Internal Transcribed Spacer 2 (ITS2)). Dadurch konnte ich in meinem ersten Projekt zeigen, dass die Assemblierungs-Prozesse mykopelagischer Flussgemeinschaften sich bereits über kürzeste Entfernungen drastisch unterscheiden und es zu einem Zusammenspiel von Umweltfaktoren sowie ökologischen Prozessen von Selektion und Verteilung kommt. In meinem zweiten Projekt habe ich neben der tag-Sequenzierung eine umfassende Literatur- und Datenbankrecherche zwecks einer globaler biogeographischer Auflösung mariner benthischer Pilze durchgeführt. Die erlaubte mir, erstmals ein konzeptionelles Bild von Verbreitungsmustern benthischer Pilze zu entwerfen. Überraschenderweise war die 100 km-Marke eine Distanz, ab der die pilzliche Verbreitung stark limitiert war. Durch eine Merkmals-Analyse konnte ich weiterhin zeigen, dass die pilzliche Verbreitung durch individuelle Merkmale wie Morphologie oder trophischer Modus signifikant beeinflusst wird. In meinem dritten Projekt habe ich erstmals den Einfluss von Anoxie auf mykobenthischen Gemeinschaften aus Küstenregionen in Inkubationsexperimenten durchgeführt. Die erhobenen Daten habe ich zusätzlich mit Meta-Gesellschaftsdaten aus publizierten Datensätzen unterfüttert. Somit konnte ich die Anpassungsfähigkeit und diverse Strategien des Mykobenthos mit anoxischen Bedingungen umzugehen, untersuchen und einzelne Keyplayer für die unterschiedlichen oxischen Bedingungen im Allgemeinen detektieren. Insgesamt unterstreicht diese Arbeit, wie wichtig das Verständnis des Zusammenwirkens räumlicher Verteilungsmuster, ökologischer Prozesse sowie diverser Umweltfaktoren ist, um die Assemblierung einzelner Pilzgemeinschaften vorherzusagen und zu modellieren. Nur dies erlaubt, verläßliche Voraussagen von sich änderenden Stoffflüssen zu machen unter der Einbeziehung aller relevanter Organismengruppen. Meine Arbeit ist ein wichtiger Bestandteil davon, denn sie eröffnen neue Sichtweisen auf pilzliche Assemblierungsprozesse, auf denen weiterführende Forschungsarbeiten aufbauen können.Dissertation289 250