Publications of Chloé Stevenne
Bookmark and Share    
Full Text
See detailCorals and Sponges Under the Light of the Holobiont Concept: How Microbiomes Underpin Our Understanding of Marine Ecosystems
Stevenne, Chloé ULiege; Micha, Maud ULiege; Plumier, Jean-Christophe ULiege et al

in Frontiers in Marine Science (2021)

In the past 20 years, a new concept has slowly emerged and expanded to various domains of marine biology research: the holobiont. A holobiont describes the consortium formed by a eukaryotic host and its ... [more ▼]

In the past 20 years, a new concept has slowly emerged and expanded to various domains of marine biology research: the holobiont. A holobiont describes the consortium formed by a eukaryotic host and its associated microorganisms including bacteria, archaea, protists, microalgae, fungi, and viruses. From coral reefs to the deep-sea, symbiotic relationships and host–microbiome interactions are omnipresent and central to the health of marine ecosystems. Studying marine organisms under the light of the holobiont is a new paradigm that impacts many aspects of marine sciences. This approach is an innovative way of understanding the complex functioning of marine organisms, their evolution, their ecological roles within their ecosystems, and their adaptation to face environmental changes. This review offers a broad insight into key concepts of holobiont studies and into the current knowledge of marine model holobionts. Firstly, the history of the holobiont concept and the expansion of its use from evolutionary sciences to other fields of marine biology will be discussed. Then, the ecology and physiology of marine holobionts will be investigated through the examples of corals and sponges. We will discuss the impacts of environmental change on organisms at the holobiont level and how microbiomes contribute to the resilience and/or vulnerability of their host in the face of environmental stressors. Finally, we will conclude with the development of new technologies, holistic approaches, and future prospects for conservation biology surrounding marine holobionts. [less ▲]

Detailed reference viewed: 29 (8 ULiège)
See detailDeciphering the expression and regulation of nitrate reductase by Symbiodiniaceae in culture and in hospite
Stevenne, Chloé ULiege; Roberty, Stéphane ULiege; Micha, Maud ULiege et al

Conference (2021)

Coral holobionts are highly efficient in the assimilation of nitrogen through heterotrophic feeding or the uptake of dissolved inorganic nitrogen. Although NO3- is the most abundant nitrogen source in the ... [more ▼]

Coral holobionts are highly efficient in the assimilation of nitrogen through heterotrophic feeding or the uptake of dissolved inorganic nitrogen. Although NO3- is the most abundant nitrogen source in the ocean, corals preferably uptake NH4+ due to its reduced state and energetically favorable assimilation. However, in conditions of low availability of environmental NH4+, coral holobionts are capable of depleting environmental NO3-. Symbiodiniaceae are vital partners of the symbiosis for nutrient assimilation. In addition to providing translocated photosynthates, they facilitate the acquisition of environmental nitrogen and account for most of the uptake of dissolved inorganic nitrogen. While the uptake of NH4+ by the coral host and its symbiotic partners is a well-known process, NO3- assimilation remains poorly studied. Coral hosts are incapable of nitrate reduction as they do not possess the necessary enzymes, while Symbiodiniaceae have been shown to express the enzyme nitrate reductase (NR). However, the evidence supporting the active reduction of nitrate by the symbiotic algae during symbiosis is scarce and equivocal. Rigorous studies on nitrate assimilation by Symbiodiniaceae are lacking yet essential for the understanding of coral holobiont functioning. We studied the expression and regulation of NR in monoclonal and axenic Symbiodiniaceae cultures (SSB01 Breviolum minutum and Symbiodinium microadriaticum) on different N sources (NO3-, NH4+, NO3- + NH4+). The algae expressed NR in culture, but the enzyme expression was repressed in the presence of NH4+ even when NO3- was available. Protein expression kinetics as well as NH4+ concentration threshold for NO3- assimilation inhibition were investigated using increasing NH4+ concentrations on NO3- medium. Following the addition of NH4+ to the medium, NR was actively degraded under 6 hours. In the absence of NH4+ and following the addition of NO3-, NR was synthesized over 3 to 6 hours. This illustrates the inhibition effect of NH4+ on NR expression. Symbiodiniaceae in culture are capable of utilizing environmental NO3-. However, the symbiotic algae could see their activity hindered by the host cellular environment and cellular NH4+ concentrations. These results raise questions about the occurrence of the enzyme NR in symbiosis along with the process of NO3- assimilation by coral holobionts. [less ▲]

Detailed reference viewed: 83 (5 ULiège)
See detailSpecific lipid and carotenoid oxidation products, and preconditioning to oxidative stress in Symbiodiniaceae
Micha, Maud ULiege; Roberty, Stéphane ULiege; Stevenne, Chloé ULiege et al

Poster (2021)

In symbiotic cnidarians, living in symbiosis with photosynthetic dinoflagellates of the Symbiodiniaceae family causes daily local hyperoxia and promotes the generation of Reactive Oxygen Species (ROS ... [more ▼]

In symbiotic cnidarians, living in symbiosis with photosynthetic dinoflagellates of the Symbiodiniaceae family causes daily local hyperoxia and promotes the generation of Reactive Oxygen Species (ROS) that, under some particular environmental conditions, may cause the breakdown of the symbiotic interaction (i.e. bleaching). Despite much effort, there are still large gaps in our understanding of ROS signaling and how the antioxidant network is modulated in Symbiodiniaceae. It is known from plants and green algae that the nature of ROS signaling depends on the chemical identity of ROS. Therefore, to understand the mechanisms by which cells sense and respond to oxidative stress, it is necessary to investigate responses to individual ROS. Under oxidative stress, oxidants such as free radicals attack polyunsaturated fatty acids (PUFAs) and carotenoids containing C-C double bonds. During this study we determined signatures that discriminate between 1O2 and hydroxyl radical-dependent lipid and carotenoid oxidation. First, we characterized the fatty acid and the carotenoid compositions in cultured and freshly isolated Symbiodinium microadriaticum by using chromatographic methods. Then we oxidized the predominant PUFAs and carotenoids in vitro by exposing them to photosynthesizer and light to generate 1O2, and H2O2 in presence of Fe3+ to generate hydroxyl radical. Finally, knowing the pattern of carotenoid and lipid oxidation products produced in vitro by 1O2 or free radicals, we looked for those oxidation products in cultured and symbiotic S. microadriaticum cells subjected to various stressful conditions such as conditions involving endogenously produced 1O2 or superoxide ion/H2O2 ; exposure to high light intensity; and high light exposure combined to elevated temperature incubation. This work also aimed to find conditions in which cells of S. microadriaticum could be preconditioned or acclimatized by ROS. To this end, different prooxidant molecules were tested. [less ▲]

Detailed reference viewed: 40 (3 ULiège)