Original title: Imaging the physiological heterogeneity of Trichodesmium and its microbial partners
Authors: HANIA, Anxhela
Document type: Doctoral theses
Year: 2025
Language: eng
Abstract: Trichodesmium is a keystone marine cyanobacterium that plays a major role in oceanic nitrogen cycling by fixing atmospheric dinitrogen (N2) in oligotrophic waters. Yet, despite decades of research, fundamental questions about how this filamentous organism coordinates N2 fixation alongside oxygenic photosynthesis remain unresolved. A central inconsistency concerns its spatial separation strategy to protect nitrogenase, the enzyme responsible for N2 fixation, from O2. Specifically, immunolabeling studies on Trichodesmium have yielded conflicting results regarding nitrogenase localization: restricted to central cells (i.e. diazocytes, heterogeneous pattern) vs. in nearly all cells (homogeneous pattern). In my thesis, I first optimized an mRNA Catalyzed Reporter Deposition Fluorescence in situ Hybridization (mRNA-based CARD-FISH) protocol to explore a new level of heterogeneity in Trichodesmium, i.e. gene expression patterns along its filament, with the goal of potentially reconciling previous conflicting findings. The investigation was directed to the detection of nifH and psbA genes, encoding the Fe-protein of nitrogenase and the D1 protein of PSII respectively, in the two strains of T. erythaeum IMS101 and NIBB1067. The overall comparison of the two strains also included growth and N2-fixing rate measurements, RT-qPCR-based gene expression analysis, Lugol's staining, and nanoscale Secondary Ion Mass Spectrometry (nanoSIMS). Secondly, I applied the CARD-FISH visual approach to examine the abundance and spatial distribution of two bacterial groups (rRNA-based CARD-FISH), Alteromonas and Roseobacter, associated with natural Trichodesmium colonies, both freshly collected and differently incubated. In doing so, I explored the potential role of these microbial interactions in facilitating the availability of iron (Fe) and phosphorus (P), essential nutrients for N2 fixation. In summary, my Ph.D. work provides new insights into Trichodesmium's physiology and highlights how the localization of associated bacteria may help to understand their role in mineral-derived nutrients.
Keywords: CARD-FISH; heterogeneity; microbial associations; N2 fixation; nanoSIMS; photosynthesis; Trichodesmium
Citation: HANIA, Anxhela. Imaging the physiological heterogeneity of Trichodesmium and its microbial partners. České Budějovice, 2025. disertační práce (Ph.D.). JIHOČESKÁ UNIVERZITA V ČESKÝCH BUDĚJOVICÍCH. Přírodovědecká fakulta

Institution: University of South Bohemia in České Budějovice (web)
Document availability information: Fulltext is available in the Digital Repository of University of South Bohemia.
Original record: http://www.jcu.cz/vskp/77682

Permalink: http://www.nusl.cz/ntk/nusl-696686


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Universities and colleges > Public universities > University of South Bohemia in České Budějovice
Academic theses (ETDs) > Doctoral theses