Etablierung eines experimentellen Systems zur Untersuchung von Endosymbiosen im Ciliaten Tetrahymena pyriformis

Endosymbiosen sind ein häufiges Phänomen innerhalb nahezu aller Organismengruppen. Besonders in Ciliaten sind diese Assoziationen sehr vielfältig und abundant. Trotz zahlreicher Untersuchungen ist wenig über die mechanistischen Ursprünge bekannt, die zur Etablierung von Endosymbiosen führen. Zudem lassen bereits seit langem bestehende Beziehungen nur wenige Rückschlüsse auf deren Entstehung zu. Um diese Phänomena studieren zu können, bedarf es eines Labormodells, das die Interaktion von Tetrahymena pyriformis mit Escherichia coli darstellt. Den ersten Schritt stellt das Entkommen des potentiellen Symbionten aus den Nahrungsvakuolen des Wirts dar. Fluoreszenz- und Transmissionselektronenmikroskopie belegen die Persistenz des Bakteriums im Cytoplasma von T. pyriformis. Dabei wird E. coli mit einer zusätzlichen Membran ausgestattet. Der Ciliat profitiert dabei von der Internalisierung antibiotikumresistenter Bakterien, in dem er selbst gesteigerte Resistenz aufweist und die toxischen Bedingungen besser überlebt. Die intrazelluläre Lebensweise beeinträchtigt die Kultivierbarkeit von E. coli auf festen Nährmedien ähnlich wie bei nahezu allen beschriebenen Endosymbionten. Um klären zu können, wie E. coli aus den Nahrungsvakuolen entkommen kann, wurden mehrere experimentelle Linien verfolgt. Hierzu wurde der Einfluss verschiedener, definierter Oberflächeneigenschaften auf die Verdauung von T. pyriformis untersucht. Dazu wurden chemisch modifizierte Mikropartikel oder Bakterien an den Ciliaten verfüttert und fluoreszenz- und transmissionselektronenmikroskopisch untersucht. Vor allem gesteigerte Hydrophobie der Zelloberfläche erhöhte die Frequenz des Entkommens aus Nahrungsvakuolen erheblich. Auch basische Substanzen beeinträchtigten die Verdauung von T. pyriformis und fördern das Entkommen aus den Phagosomen, indem das Ansäuern dieser beeinträchtigt wird. Insgesamt spielen Zelloberflächen eine wichtige Rolle beim Initiieren von Endosymbiosen

Population–reaction model and microbial experimental ecosystems for understanding hierarchical dynamics of ecosystems

Understanding ecosystem dynamics is crucial as contemporary human societies face ecosystem degradation. One of the challenges that needs to be recognized is the complex hierarchical dynamics. Conventional dynamic models in ecology often represent only the population level and have yet to include the dynamics of the sub-organism level, which makes an ecosystem a complex adaptive system that shows characteristic behaviors such as resilience and regime shifts. The neglect of the sub-organism level in the conventional dynamic models would be because integrating multiple hierarchical levels makes the models unnecessarily complex unless supporting experimental data are present. Now that large amounts of molecular and ecological data are increasingly accessible in microbial experimental ecosystems, it is worthwhile to tackle the questions of their complex hierarchical dynamics. Here, we propose an approach that combines microbial experimental ecosystems and a hierarchical dynamic model named population–reaction model. We present a simple microbial experimental ecosystem as an example and show how the system can be analyzed by a population–reaction model. We also show that population–reaction models can be applied to various ecological concepts, such as predator–prey interactions, climate change, evolution, and stability of diversity. Our approach will reveal a path to the general understanding of various ecosystems and organisms

Metabolic mechanisms for the evolution of stable symbiosis

Endosymbiosis involves the merger of once independent organisms; this evolutionary transition has defined the evolutionary history of eukaryotes and continues to underpin the function of a wide range of ecosystems. Endosymbioses are evolutionarily dynamic because the inherent conflict between the self-interest of the partners make the breakdown of the interaction ever-likely and this is exacerbated by the environmental context dependence of the benefits of symbiosis. This necessitates selection for partner switching, which can reshuffle the genetic identities of symbiotic partnerships and so rescue symbioses from cheater-induced extinction and enable rapid adaptation to environmental change. However, the mechanisms of partner-specificity, that underlie the potential for partner switching, are unknown. Here I report the metabolic mechanisms that control partner specificity within the tractable microbial photosymbiosis between Paramecium bursaria and Chlorella . I have found that metabolic function, and not genetic identity, enables partner-switching, but that genetic variation plays an important role in maintaining variation in symbiotic phenotype. In addition, I observed that symbiont stress-responses played an important role in partner specificity, and that alleviating symbiont stress responses may be an important strategy of generalist host genotypes. Furthermore, I have used experimental evolution to show that a novel, initially non-beneficial association can rapidly evolve to become a beneficial symbiosis. These results demonstrate that partner integration is defined by metabolic compatibility and that initially maladapted host-symbiont pairings can rapidly evolve to overcome their lack of co-adaptation through alterations to metabolism and symbiont regulation. Understanding the process of novel partner integration and partner switching is crucial if we are to understand how new symbioses originate and stabilise. Moreover, mechanistic knowledge of partner switching is required to mitigate the breakdown of symbioses performing important ecosystem functions driven by environmental change, such as in coral reef

Taxonomy and Ecology of Marine Algae

The term “algae” refers to a large diversity of unrelated phylogenetic entities, ranging from picoplanktonic cells to macroalgal kelps. Marine algae are an important primary producer in the marine food chain, responsible for the high primary production of coastal areas, providing food resources in situ for many grazing species of gastropods, peracarid crustaceans, sea urchins or fish. Recent findings indicate that marine environments have rapidly changed due to global warming over the past several decades. This change has led to significant variations in marine algal ecology. For example, a long-term increase in ocean temperatures due to global warming has facilitated the intensification of harmful algal blooms, which adversely impact public health, aquatic organisms, and aquaculture industries. Thus, extensive studies have been conducted, but there is still a gap in our understanding of the variation in their ecology in accordance with future marine environmental changes. To fill this gap, studies on the taxonomy and ecology of marine algae are highly necessary. We have invited algologists to submit research articles that enable us to advance our understanding of the taxonomy and ecology of marine algae. Fourteen papers have been collected so far, which cover different aspects of the taxonomy and ecology of marine algae, including understudied species, interspecific comparisons, and new techniques