In March 2026, we welcomed more than 130 on-site and virtual participants for the EMBO | EMBL Symposium ‘The cellular mechanics of symbiosis: sensing friend from foe‘. Held in Heidelberg, the meeting brought together researchers from around the world to explore the evolution and mechanisms of intimate species–species interactions.

The programme featured two keynote speakers and 15 invited speakers, who guided participants through the complexities of symbiotic function, including immunity and pathogenesis in symbiosis, how symbionts can be harnessed for benefit, and shared principles across different symbiotic systems.

The symposium also showcased 52 posters, offering a broad snapshot of current research in the field. Five poster prize winners were selected, and we are happy to introduce three of them in this post.

Establishment of an orthogonal synthetic platform in mammalian cells to study the role of Endosymbiont Targeted Proteins (ETPs) in the survival of the endosymbiont in the host cells

Presenter: Rudvi Pednekar

Authors: Rudvi Pednekar, Leonie-Alexa Koch, Natascha Künzel, Eva Nowack, Matias Zurbriggen

Abstract:

The evolution of eukaryotic life has been influenced by endosymbiosis. Retracing their history, early organelle development poses challenges. Novel model systems are needed to study initial host-endosymbiont interactions that lead to stable integration. Angomonas deanei is an emerging model organism that harbours a β-proteobacterial endosymbiont, Candidatus Kinetoplastibacterium crithidii. Identifying mechanisms for endosymbiont survival and growth is crucial for a sustainable relationship. Angomonas has seen Endosymbiont Targeted Proteins (ETPs) that target the endosymbiont. Some ETPs regulate endosymbiont division, but the functions of others remain unknown. Limited tools for genetic manipulation and complex protein interactions hinder studies in Angomona s. Our project aims to reconstruct endosymbiosis in mammalian cells using synthetic biology. This system provides an orthogonal platform for studying cellular organisation and regulation, focusing on host-symbiont interactions such as nuclear control of endosymbiont division and ETP localisation, while avoiding crosstalk with the endogenous Angomonas network. This bottom-up approach will help identify the minimal requirements for establishing a stable host-endosymbiont interaction while utilising the versatile toolkit for manipulating mammalian systems. In this orthogonal system, we investigated interactions between individual ETPs or groups of ETPs using co-localisation and FRET-based assays. In addition to constitutively expressing ETPs, we developed light-controllable ETPs using optogenetics, allowing precise, reversible manipulation of ETP expression and interactions for an enhanced genetic control platform.
To facilitate the introduction of the A. deanei-derived endosymbiont in mammalian cells, we established a non-invasive, mid-throughput fusion protocol using polyethylene glycol (PEG). We successfully validated the protocol by delivering E. coli and the endosymbiont from the Ca.K.crithidi into HeLa cells. With this robust orthogonal platform, our goal is to identify key host-endosymbiont components to guide evolution and aid in the creation of synthetic symbiosis systems.

Due to the confidentiality of the unpublished data, we cannot share the poster.

Poster prize kindly sponsored by FEBS Letters

Experimental Sodalis infection eliminates ancient insect symbiont

Presenter: Ronja Krüsemer

Authors: Ronja Krüsemer, Ana Carvalho, Jean Keller, Heiko Vogel, Colin Dale, Tobias Engl, Martin Kaltenpoth

Abstract:

Many insects benefit from ancient nutrient-supplementing endosymbionts. In many cases, these mutualistic associations are obligate, and host and microbial symbiont have become metabolically dependent on each other via coevolution. Despite the obligate nature of many intracellular insect symbioses, ancient symbionts can be replaced by other microbes. While symbiont losses and replacements occur in evolutionary timescales, their dynamics remain enigmatic due to the lack of experimentally tractable systems. Here, we report on the experimental establishment of the culturable bacterium Sodalis praecaptivus in a grain beetle (Oryzaephilus surinamensis) and its effect on the native symbiont Shikimatogenerans silvanidophilus, which produces the tyrosine precursor prep henate. Injection of Sodalis into female beetles led to systemic intracellular infection and efficient transovarial vertical transmission, but also reduced host survival and reproduction. Interestingly, Sodalis invaded the host’s bacteriomes, causing irregular morphology and rapid loss of the native symbiont Shikimatogenerans within three beetle generations. Transcriptomics revealed a strong upregulation of host immune effectors upon Sodalis infection, but little reaction from Shikimatogenerans, indicating that the ancient symbiont is incapable of responding adaptively to the introduced competitor. The rapid elimination of the native symbiont in O. surinamensis showcases the fragility of ancient beneficial symbioses and experimentally recapitulates a crucial step towards a functional symbiont replacement.

View poster

Fragmented but functional- Interdependent symbionts complement missing genes

Presenter: Dongik Chang

Authors: Dongik Chang, Julian Kiefer, Veit Grabe, Benjamin Weiss, Severine Balmand, Thomas Pertsch, Anna Zaidman-Rémy, Martin Kaltenpoth, Tobias Engl

Abstract:

Many insects have evolved in beneficial associations with microorganisms, including the supplementation of essential nutrients. Some grain pest beetles have successfully adapted to dry conditions due to their thick cuticles, attributed to their ancient endosymbiont. Among the grain pest beetles with tyrosine-supplementing symbionts, Prostephanus truncatus harbors the ancient symbiont, Shikimatogenerans bostrichidophilus, which diverged into three lineages with reduced genome sizes. Symbiont genome analyses revealed complementary gene distributions, resulting in interdependent metabolic pathways among the three strains. However, experimental manipulation of the symbionts verified the functional integrity and contribution to cuticle supplementation of this fragmented symbiosis. By applying different imaging techniques, we present potential mechanisms of interactions among the interdependent bacteria and illustrate their temporal and spatial dynamics. We employed different Fluorescence in situ hybridization (FISH) techniques to localize bacterial lineage-specific DNA and RNA molecules. Moreover, 3D imaging of symbiotic organs revealed temporal changes in symbiont cell structure, which may be closely related to high metabolic exchange and the successful transmission of symbionts to reproductive organs. The results suggest that Prostephanus necessarily needs to maintain and transmit three lineages of symbionts and coordinate metabolic exchange with and between them. To further understand the mechanism of exchanging complementary molecules, we imaged the ultrastructure of the symbiotic organs using TEM, SEM, and FIB SEM imaging. Our findings suggest that these interdependent symbionts may cooperate via vesicles and dynamic connections among the symbiont cells. It remains unresolved whether single steps of the evolutionary processes leading to such strain divergence are beneficial or if this phenomenon is a non-adaptive, degenerative process of symbiosis breakdown, accompanied by compensatory adaptations during its evolutionary senescence.

Due to the confidentiality of the unpublished data, we cannot share the poster.

The EMBO | EMBL Symposium ‘The cellular mechanics of symbiosis: sensing friend from foe‘ took place from 17 – 20 March 2026 at EMBL Heidelberg and virtually.