Identifying metabolic interactions in the microalgae-Endozoicomonas relationship

We are looking for one Master 2 student in a project financed by the Agence Nationale de la Recherche.

Duration: 5 months (September 2025 – January 2026)

Identifying metabolic interactions in the microalgae-Endozoicomonas relationship

Background
Coral reef ecosystems are critically threatened by the effects of global climate change. As corals are long-lived organisms, it is likely that the current rate of climate change is rapidly outpacing the genetic adaptive capacity of corals. In recent years, non-genetic adaptation mechanisms, such as epigenetic mechanisms, phenotypic plasticity and changes in microbial communities and interactions, have been increasingly discussed as potential venues of adaptive reef conservation. Reef-building corals are holobionts that associate with a highly diverse microbial community that includes intracellular algae (Dinoflagellata: Symbiodiniaceae), bacteria, archaea, fungi and viruses. Decades of functional research testify to the importance of the coral-algal symbiosis, a nutrient exchange relationship that forms the functional basis of coral reef formation. However, our understanding of the functions and interactions of other microbes in the holobiont remains limited. It is only in recent decades that coral reef ecology has broadened to consider the potential role of other microbial members in the health, resilience and acclimatization of the coral holobiont. Despite a fair understanding of the dynamics of coral-associated bacterial communities and their responses to environmental change, the metabolic interactions of bacteria in the coral holobiont remain a significant knowledge gap, and experimental data supporting the mutualistic lifestyles of bacteria in corals are largely lacking.

Approach
The complex holobiont nature of corals poses a serious challenge to functional studies of microbes in the coral holobiont. To permit a controlled environment, the proposed work leverages on a new temperate model system for photosymbiosis consisting of the sea anemone Aiptasia couchii, and isolates of its native algal symbiont, Philozoon adriaticum (AM-7D) and two distinct isolates of the gram-negative bacterium Endozoicomonas (API- and API-). All cultures are available at the lab.

Bleaching is a general stress response of corals holobionts that is most commonly observed under heat stress. Bleaching is manifested in the loss of algal symbionts from the coral tissues and/or photosynthetic pigment from the algae. At the same time, Endozoicomonas is one of the most consistently associated bacteria associated with Cnidaria globally and can exhibit overproportionate high abundances in the tissues of corals. While different functions of Endozoicomonas such as nutrient cycling, antioxidant activity, and sulfur cycling have been proposed, we ultimately do not understand its exact role in the cnidarian holobiont.
In corals, bleaching, i.e. the loss of algal symbionts often coincides with the loss of Endozoicomonas. While Endozoicomonas is not typically a member of the microbiome of the algal symbiont, we know that the bacterium is often localized near the algae. This suggests that the two entities, that is the algae and Endozoicomonas, may interact with each other, potentially through the exchange of metabolites as often observed in phytoplankton and associated bacteria. As such, the objective of this project is to determine potential metabolic interactions and resulting physiological responses between the algal symbiont Philozoon cf. adriaticum and Endozoicomonas in co-culture.

Combining physiological parameters of the algae (growth rates, photochemistry, chlorophyll content) with untargeted metabolomic tools, this project will address the following questions:
i) Does co-culture with Endozoicomonas have beneficial effects on algal symbiont physiology?
ii) Does co-culture of Philozoon adriaticum and Endozoicomonas affect the metabolite profiles of both organisms?

This project will identify candidate metabolites potentially involved in the algal symbiont-Endozoicomonas relationship within the cnidarian holobiont.

Principal Investigator: ANR Junior Professor Chair (CPJ) Dr. Claudia Pogoreutz, CRIOBE, Université de Perpignan Via Domitia, France

This internship opportunity will take place in the Marine Interactomes Group of the CRIOBE, which is an international team.

Interested? Please send your CV and a letter of motivation explaining why you are interested in this position to: claudia.pogoreutz@univ-perp.fr

Deadline: 20 May 2025

Further reading:
– Porras, M. Á. G., Assié, A., Tietjen, M., Violette, M., Kleiner, M., Gruber-Vodicka, H., … & Leisch, N. (2024). An intranuclear bacterial parasite of deep-sea mussels expresses apoptosis inhibitors acquired from its host. Nature Microbiology, 1-15.
– Pogoreutz, C., & Ziegler, M. (2024). Frenemies on the reef? Resolving the coral–Endozoicomonas association. Trends in Microbiology, 32(5), 422-434.
– Pogoreutz, C., Oakley, C. A., Rädecker, N., Cárdenas, A., Perna, G., Xiang, N., … & Voolstra, C. R. (2022). Coral holobiont cues prime Endozoicomonas for a symbiotic lifestyle. The ISME Journal, 16(8), 1883-1895.
– Hochart, C., Paoli, L., Ruscheweyh, H. J., Salazar, G., Boissin, E., Romac, S., … & Galand, P. E. (2023). Ecology of Endozoicomonadaceae in three coral genera across the Pacific Ocean. Nature Communications, 14(1), 3037.
– Shibl, A. A., Isaac, A., Ochsenkuhn, M. A., Cárdenas, A., Fei, C., Behringer, G., … & Amin, S. A. (2020). Diatom modulation of select bacteria through use of two unique secondary metabolites. Proceedings of the National Academy of Sciences, 117(44), 27445-27455.