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  • 1
    Publication Date: 2019-02-04
    Description: Most eukaryotic species are colonized by a microbial community – the microbiota – that is acquired during early life stages and is critical to host development and health. Much research has focused on the microbiota biodiversity during the host life, however, empirical data on the basic ecological principles that govern microbiota assembly is lacking. Here we quantify the contribution of colonizer order, arrival time and colonization history to microbiota assembly on a host. We established the freshwater polyp Hydra vulgaris and its dominant colonizer Curvibacter as a model system that enables the visualization and quantification of colonizer population size at the single cell resolution, in vivo, in real time. We estimate the carrying capacity of a single Hydra polyp as 2 × 105 Curvibacter cells, which is robust among individuals and time. Colonization experiments reveal a clear priority effect of first colonizers that depends on arrival time and colonization history. First arriving colonizers achieve a numerical advantage over secondary colonizers within a short time lag of 24 h. Furthermore, colonizers primed for the Hydra habitat achieve a numerical advantage in the absence of a time lag. These results follow the theoretical expectations for any bacterial habitat with a finite carrying capacity. Thus, Hydra colonization and succession processes are largely determined by the habitat occupancy over time and Curvibacter colonization history. Our experiments provide empirical data on the basic steps of host-associated microbiota establishment – the colonization stage. The presented approach supplies a framework for studying habitat characteristics and colonization dynamics within the host–microbe setting.
    Type: Article , PeerReviewed
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  • 2
    Publication Date: 2019-02-06
    Description: Benthic foraminifera are unicellular eukaryotes inhabiting sediments of aquatic environments. Several species were shown to store and use nitrate for complete denitrification, a unique energy metabolism among eukaryotes. The population of benthic foraminifera reaches high densities in oxygen-depleted marine habitats, where they play a key role in the marine nitrogen cycle. However, the mechanisms of denitrification in foraminifera are still unknown, and the possibility of a contribution of associated bacteria is debated. Here, we present evidence for a novel eukaryotic denitrification pathway that is encoded in foraminiferal genomes. Large-scale genome and transcriptomes analyses reveal the presence of a denitrification pathway in foraminifera species of the genus Globobulimina. This includes the enzymes nitrite reductase (NirK) and nitric oxide reductase (Nor) as well as a wide range of nitrate transporters (Nrt). A phylogenetic reconstruction of the enzymes' evolutionary history uncovers evidence for an ancient acquisition of the foraminiferal denitrification pathway from prokaryotes. We propose a model for denitrification in foraminifera, where a common electron transport chain is used for anaerobic and aerobic respiration. The evolution of hybrid respiration in foraminifera likely contributed to their ecological success, which is well documented in palaeontological records since the Cambrian period.
    Type: Article , PeerReviewed
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  • 3
    Publication Date: 2019-08-20
    Description: Benthic foraminifera populate a diverse range of marine habitats. Their ability to use alternative electron acceptors—nitrate (NO3−) or oxygen (O2)—makes them important mediators of benthic nitrogen cycling. Nevertheless, the metabolic scaling of the two alternative respiration pathways and the environmental determinants of foraminiferal denitrification rates are yet unknown. We measured denitrification and O2 respiration rates for 10 benthic foraminifer species sampled in the Peruvian oxygen minimum zone (OMZ). Denitrification and O2 respiration rates significantly scale sublinearly with the cell volume. The scaling is lower for O2 respiration than for denitrification, indicating that NO3− metabolism during denitrification is more efficient than O2 metabolism during aerobic respiration in foraminifera from the Peruvian OMZ. The negative correlation of the O2 respiration rate with the surface/volume ratio is steeper than for the denitrification rate. This is likely explained by the presence of an intracellular NO3− storage in denitrifying foraminifera. Furthermore, we observe an increasing mean cell volume of the Peruvian foraminifera, under higher NO3− availability. This suggests that the cell size of denitrifying foraminifera is not limited by O2 but rather by NO3− availability. Based on our findings, we develop a mathematical formulation of foraminiferal cell volume as a predictor of respiration and denitrification rates, which can further constrain foraminiferal biogeochemical cycling in biogeochemical models. Our findings show that NO3− is the preferred electron acceptor in foraminifera from the OMZ, where the foraminiferal contribution to denitrification is governed by the ratio between NO3− and O2.
    Type: Article , PeerReviewed
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  • 4
    Publication Date: 2019-09-23
    Description: The aim of R/V Alkor cruise AL438 was to investigate the assemblage composition, population density and distribution of Recent benthic foraminifera in the Elbe estuary and southern North Sea. We focused on an assessment of the present state of the ecosystems and a comparison with data from former decades. Our work resumed investigations of the Geologisch-Paläontologisches Institut of Kiel University and the Federal Hydrographic Office from 1960s till the 1980s, as well as topical studies to the west of Helgoland. We revisited the same stations and took sediment samples with historical and modern grab samplers, box corer, Minicorer and a gravity corer. These samples were accomplished with samples from new stations in order to describe the relationships of foraminiferal faunas living in the Helgoland mud area with those inhabiting the surrounding sands. The sampling was accompanied with hydrographical measurements and water sampling to document relevant environmental parameters. The foraminiferal sampling was carried out for the first time following of the FOraminiferal BIoMOnitoring group (FOBIMO) recommendations as much as possible, in order to test the practicability of the guidelines. In total, 109 deployments at 37 stations were successfully accomplished.
    Type: Report , NonPeerReviewed , info:eu-repo/semantics/book
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  • 5
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    In:  (Master thesis), Christian-Albrechts-Universität Kiel, Kiel, Germany, 77 pp
    Publication Date: 2019-09-23
    Keywords: Course of study: MSc Biological Oceanography
    Type: Thesis , NonPeerReviewed
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  • 6
    Publication Date: 2019-10-08
    Description: Highlights: Inspired by the evolution of eukaryotic organelles, we propose a conceptual framework to study the evolutionary and ecological drivers of symbiosis, including three main elements: a currency, mechanisms of currency exchange, and inheritance. Currency in symbiosis is the type resources that species in a beneficial symbiosis gain from their partner. Currency exchange is a complex process that requires molecular adaptations in one or both partners. We identify two distinct but not mutually exclusive initial evolutionary imperatives for the establishment of symbiosis, termed currency first, in which the initial interaction stems from a common currency exchange between the interacting partners to complement their environmental requirements, and transmission first, in which stable transgenerational transmission precedes the evolution of currency exchange. Symbiotic interactions between eukaryotes and prokaryotes are widespread in nature. Here we offer a conceptual framework to study the evolutionary origins and ecological circumstances of species in beneficial symbiosis. We posit that mutual symbiotic interactions are well described by three elements: a currency, the mechanism of currency exchange, and mechanisms of symbiont inheritance. Each of these elements may be at the origin of symbiosis, with the other elements developing with time. The identity of currency in symbiosis depends on the ecological context of the symbiosis, while the specificity of the exchange mechanism underlies molecular adaptations for the symbiosis. The inheritance regime determines the degree of partner dependency and the symbiosis evolutionary trajectory. Focusing on these three elements, we review examples and open questions in the research on symbiosis.
    Type: Article , PeerReviewed
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