Dr. Sebastian Fraune

fraune2Zoologisches Institut der Universität zu Kiel
Am Botanischen Garten 9
24118 Kiel
Tel 0431-880-4149
Fax 0431-880-4747

                                                             Research      Publications      Curriculum vitae      Outreach


My research is focusing on the understanding of host-microbe interactions. In many animals epithelial tissues are colonized by complex communities of microbes. The diversity of microbes colonizing a host is proposed to be a result of coevolution between the eukaryotic host and the colonizing microbial community, influenced by both environment and host. These microbes influence the fitness of their hosts, ultimately forming a metaorganism consisting of a multicellular host and a community of associated microorganisms. The basis of my approach is the hypothesis that molecular host-microbe communications select for a core microbiota in a given host species which contributes to host fitness and adaptation. Since cnidaria belong to the early-branching metazoan and have preserved much of the genetic complexity of the common metazoan ancestor they promise to be highly informative for the analysis of epithelial host-microbe interactions. Using the two cnidarian model systems Hydra and Nematostella, I aim to understand the evolution and function of metaorganisms.

Sebastian1Cnidaria have the simplest epithelia in the animal kingdom, with only two cell layers. While changes in the cell composition led to significant modulation of the microbial community, we hypothesize that a stable bacterial colonization is mainly controlled by the host genotype and that a direct interaction between host epithelia and microbiota exists. The innate immune system as the host’s first line of contact with the microbiota is expected to play a crucial role in the selection of the microbiota. We have shown, that antimicrobial peptides, in general, are not only killers but are the selective force and maintenance factor for stable microbial communities. As AMPs are important effectors of innate immunity throughout the animal kingdom, we propose that the secretion of specific AMPs reflect habitat-specific adaptations to facilitate the control of habitat-specific bacterial colonizers.

(see Franzenburg S, et al. (2013) PNAS, 110(39):E3730-8, Franzenburg S, et al. (2012) PNAS, 109 (47):19374-9, Fraune S, et al. (2010) PNAS, 107,18067-18072, 17 and Fraune S, et al. (2009) Environ. Microbiol. 11: 2361-2369.

Current research projects

The role of quorum sensing (QS) / quorum quenching (QQ) in the metaorganism Hydra
HydraEpithelial surfaces of most animals are colonized by specific bacterial communities. Therefore, it is important for the host to control both the composition and behavior of bacterial colonizers. Many gram-negative bacteria are able to coordinate their behavior using fatty-acid-derived signaling molecules of the acyl homoserine lactone (AHL) family. This cell-density-based gene regulation is known as quorum sensing (QS). Degradation of QS signals results in quorum quenching (QQ). It was proposed that bacteria produce QQ enzymes as a self-modulatory system of their own QS system, but also eukaryotic tissues seem to be able to interfere with the bacterial QS signaling directly. Up to know, only few host mechanisms targeting the communal behavior of bacteria have been identified. In this project we investigate how an animal can manipulate quorum sensing signals produced by colonizing bacteria. Using the early branching metazoan Hydra as a model, we identified a new eukaryotic quorum quenching mechanism which enables Hydra to specifically modify long-chain 3-oxo-homoserine lactones. In contrast, whole genome sequencing of Hydra’s main bacterial colonizer Curvibacter sp. revealed the presence of a complete QS machinery. Functional characterization of the QS system of Curvibacter sp. showed that both, the host-modified and the non-modified N-acyl-homoserine lactone (AHLs), were recognized by the same AHL-receptors. Remarkably, even though both AHLs were recognized by the same receptors, the gene expression induced by the different AHLs led the induction of different bacterial phenotypes. These results show that Hydra is able to regulate the behavior of its bacterial colonizers. Currently we are investigating the QQ activity of Hydra in vivo in more depth (together with the group of Andreas Tholey, Systematische Proteomics und Bioanalytik, Uni Kiel) and investigate the influence of host AHL modification for the metaorganism assembly and resilience.

Beyond the genome: impact of microbial communities and epigenetic regulations for adaptation (see Mortzfeld BM et al 2015)
NematostellaThe phenotype of an animal cannot be explained entirely by its genes. It is now clear that factors other than the genome contribute to the development and the dynamic homeostasis of multicellular animals. Two fundamentally important factors are epigenetic regulations and the microbial communities associated with the animal. Unlike the genes and regulatory regions of the genome, epigenetics and microbial composition can be rapidly modified by environmental cues, and may thus represent mechanisms for rapid acclimation of individuals to a changing environment. At present, the individual functions of epigenetics, microbiomes, and genomic mutations are largely studied in isolation, particularly for species in marine ecosystems. This leaves significant questions open for how these mechanisms intersect in the acclimation and adaptation of organisms to environmental changes. The aim of this research is to determine how epigenetic regulations and microbial communities participate in thermal acclimation of a coastal marine species residing in a dynamic temperature environment, and how these non-genetic factors interact with each other. The model species used for this study, the sea anemone Nematostella vectensis, enables us to carry out unprecedented functional experiments to dissect the interactions between microbes and epigenetic mechanisms in the acclimation of the holobiont.

The role of development specific immune responses for stage specific bacterial colonization (see Mortzfeld BM et al 2015)
Transgenic NVMarine invertebrates are in constant contact with a vast number of highly diverse microbes in their environment. As such, they are ideal models for examining prokaryote-eukaryote interactions. The establishment of host-bacterial colonization during development is a fundamental process influencing the fitness of many organisms, but the factors controlling community membership and influencing the establishment of the microbial ecosystem during development are poorly understood. We have started to investigate the host molecular mechanisms involved in bacterial recognition and establishment in the marine model system Nematostella vectensis. By investigating the bacterial colonization from the earliest developmental stages to one year old adult polyps under different environmental conditions, we could clearly demonstrate the robust colonization process in Nematostella. The clear separation of bacterial communities of early developmental stages, juvenile and adult polyps is correlated to major transitions within the development of Nematostella, mostly independent of environmental factors. Thus, we hypothesize that the age dependent bacterial colonization in Nematostella is reflecting development dependent changes in the innate immune system. Therefore, one of the aims of this project is to characterize the immune system of Nematostella depending on the developmental age. We will concentrate on the immune response to bacterial colonization and on bacterial recognition. Both aspects will be analyzed at different developmental stages to assess dynamic development-dependent changes within the immune system.


BIOL12           BIOL8




  • Mortzfeld B, Urbanski S, Reitzel AM, Künzel S, Technau U, Fraune S (2015). Response of bacterial colonization in Nematostella vectensis to development, environment and biogeography. Environ. Microbiol., 2015 Jun 1. doi: 10.1111/1462-2920.12926.
  • Li X-Y, Pietschke C, Fraune S, Altrock PM, Bosch TCG, Traulsen A (2015). Which games are growing bacterial populations playing? J. Royal Society Interface (in press)
  • Fraune S, Franzenburg S, Schröder S, Augustin R, Anton-Erxleben F, Bosch TCG (2014). Bacteria-bacteria interactions within the microbiota of the ancestral metazoan Hydra contribute to fungal resistance. ISME J., 2014 Dec 16. doi: 10.1038/ismej.2014.239.
  • Grasis J, Lachnit T, Anton-Erxleben F, Lim YM, Schmieder R, Fraune S, Franzenburg S, Insua S, Machado G, Haynes M, Little M, Kimble R, Rosenstiel P, Rohwer FL, Bosch TCG (2014). Species-Specific Viromes in the Ancestral Holobiont Hydra. PLoS ONE, 9(10):e109952
  • Bosch TCG, Adamska M, Augustin R, Domazet-Loso T, Foret S, Fraune S, Funayama N, Grasis J, Hamada H, Hatta H, Hobmayer B, Kawai K, Klimovich A, Manuel M, Shinzato C, Technau U, Yum S, and Miller DJ (2014). How do environmental factors influence life cycles and development? An experimental framework for early-diverging metazoans. Bioessays. 2014 Sep 10. doi: 10.1002/bies.201400065.
  • Franzenburg S, Walter J, Künzel S, Wang J, Baines JF, Bosch TCG, Fraune S (2013). Distinct antimicrobial peptide expression determines host species-specific bacterial associations. Proc Natl Acad Sci USA, 110(39):E3730-8
  • Franzenburg S*, Fraune S*, Altrock PM, Künzel S, Baines JF, Traulsen A, Bosch TCG (2013). Bacterial colonization of Hydra hatchlings follows a robust temporal
    pattern. ISME Journal, doi: 10.1038/ismej.2012.156
  • Franzenburg S*, Fraune S*, Künzel S, Baines JF, Domazet-Lošo T, Bosch TCG (2012). MyD88 deficient Hydra reveal an ancient function of TLR-signaling in sensing bacterial colonizers. Proc Natl Acad Sci USA,109 (47): 19374-9
  • Fraune J, Alsheimer M, Volff JN, Busch K, Fraune S, Bosch TCG, Benavente R (2012). Hydra meiosis reveals unexpected conservation of structural synaptonemal complex proteins across metazoans. Proc Natl Acad Sci USA, 109:16588-16593
  • Fraune S, Augustin R, Bosch TCG (2011). Embryo protection in contemporary immunology: Why bacteria matter. Communicative & Integrative Biology (4):369-72
  • Fraune S , Augustin R, Anton-Erxleben F, Wittlieb J, Gelhaus C, Klimovich VB, Samoilovich MP, and Bosch TCG (2010). In an early branching metazoan, bacterial colonization of the embryo is controlled by maternal antimicrobial peptides. Proc. Natl. Acad. Sci. USA, 107,18067-18072; Featured as “Research Highlights” in Nature Immunology (2010) 11, 1083
  • Fraune S and Bosch TCG (2010). Why bacteria matter in animal development and evolution. Bioessays, 32 (7): 571-80
  • Chapman JA , Kirkness EF, Simakov O, … Khalturin K, Hemmrich G, Franke A, Augustin R, Fraune S, ..Venter JC, Technau U, Hobmayer B, Bosch TCG, Holstein TW, Fujisawa T, Bode HR, David CN, Rokhsar DS, Steele RE (2010). The dynamic genome of Hydra. Nature, 464(7288):592-6
  • Augustin R, Fraune S, and Bosch TCG (2010). How Hydra senses and destroys microbes. Sem. Immunol., 22: 54–58
  • Khalturin K, Hemmrich G, Fraune S and Bosch TCG (2009). More than just orphans: are taxonomically-restricted genes important in evolution? Trends in Genetics, 25: 404-413
  • Fraune S, Abe Y, Bosch TCG (2009). Disturbing epithelial homeostasis in the metazoan Hydra leads to drastic changes in associated microbiota. Environ. Microbiol., 11: 2361-2369
  • Jaenicke E*, Fraune S*, May S, Irmak P, Augustin R, Meesters C, Decker H, and Zimmer M (2009). Is activated hemocyanin instead of phenoloxidase involved in immune response in woodlice? Dev. Comp. Immunol., 33(10):1055-63
  • Anton-Erxleben F, Thomas A, Wittlieb J, Fraune S, Bosch TCG (2009). Plasticity of epithelial cell shape in response to upstream signals: a whole-organism study using transgenic Hydra. Zoology, 112: 185-94
  • Bosch TCG, Augustin R, Anton-Erxleben F, Fraune S, Hemmrich G, et al (2009). Uncovering the evolutionary history of innate immunity: the simple metazoan Hydra uses epithelial cells for host defence. Dev. Comp. Immunol. 33: 559-69
  • Fraune S and Zimmer M (2008). Host-specificity of environmentally transmitted Mycoplasma-like isopod symbionts. Environ. Microbiol. 10: 2497-504
  • Fraune S and Bosch TCG (2007). Long-term maintenance of species-specific bacterial microbiota in the basal metazoan Hydra. Proc. Natl. Acad.Sci. USA 104: 13146-51

* authors contributed equally

Non-peer reviewed publications

  • Bosch TCG, Fraune S (2014) Why bacteria matter: insights from the Hydra holobiont. Old Herborn University Seminar Monograph 27, 113-123
  • Fraune S, Bosch TCG (2012) Host-symbiont interactions: why cnidaria matter, Cell News 3:14-21
  • Augustin R, Fraune S, Franzenburg S, Bosch TCG (2012) Where simplicity meets complexity: hydra, a model for host-microbe interactions. Adv Exp Med Biol. 710:71-81.
  • Bosch TCG, Anton-Erxleben F, Augustin F, Franzenburg S & Fraune S (2011) Hydra Go Bacterial, in E. Rosenberg & U. Gophna (eds.), Beneficial Microorganisms in Multicellular Life Forms, 313-322
  • Fraune S, Franzenburg S, Augustin R and Bosch TCG (2011) Das Prinzip Metaorganismus. BIOSPEKTRUM 17: 634-636
  • Fraune S, Augustin R, and Bosch TCG (2009) Exploring host-microbe interactions in Hydra. Microbe 4(10), 457-462

Oral presentations in international meetings

  • International Workshop “Holobiont dynamics and impact on ¬fitness”, Montpellier, France (2015). “Cnidarian microbiome: assembly, coevolution and function” (invited talk)
  • International Workshop “Animal evolution: New perspectives from early emerging metazoans”, Evangelische Akademie Tutzing, Germany (2015). “Response of bacterial colonization in Nematostella vectensis to development, environment and biogeography”
  • CNRS – Jacques Monod Conference “Marine eco-systems biology”, Roscoff, France (2015) “Cnidarian microbiome: assembly, coevolution and function” (invited talk)
  • American Society for Microbiology General Meeting, Boston, USA (2014) “Host mechanisms controlling bacterial colonizers in the basal metazoan Hydra” (invited talk), chair of session 159: “Shaping of the Microbiome through Host Immunity”
  • International Workshop “Unravelling the Developmental Regulatory Network in Early Animals”, Evangelische Akademie Tutzing, Germany (2013). “Host selection of species-specific bacterial colonizers in the cnidarian Hydra”
  • DZG Meeting Evolutionary Biology, Göttingen, Germany (2013). “Host selection of species-specific bacterial colonizers in the cnidarian Hydra” (invited talk)
  • International Workshop “Searching for eve: Basal Metazoans and the Evolution of Multicellular Complexity”, Evangelische Akademie Tutzing, Germany (2011) “Host derived mechanisms controlling host-bacterial homeostasis at the epithelial interface in Hydra”
  • The 4th International Symposium of the Biodiversity & Evolution Global COE Project Kyoto, Japan (2010) “How do basal metazoan sense and interact with their associated microbiota?” (invited talk)
  • 3rd Biannual Symposium “Future Ocean”, Kiel, Germany (2010) “Hydra is controlling bacterial colonization during early embryogenesis”
  • International Workshop “The Evolution of Multicellularity: Insights from Hydra and other Basal Metazoans”, Evangelische Akademie Tutzing, Germany (2009) “Hydra – a community affair”
  • 11th Congress of the International Society of Developmental and Comparative Immunology, Prague, Czech Republic (2009) “Towards understanding a Holobiont: Host-Microbe Interactions in the early branching metazoan Hydra”
  • 2nd ASM Conference on Beneficial Microbes, San Diego, USA (2008) “Towards understanding a Holobiont: Host-Microbe Interactions in the early branching metazoan Hydra”
  • International Workshop “Hydra and the Development of Animal Form”, Evangelische Akademie Tutzing, Germany (2007) “Hydra-associated microbes: a metagenomic project”
  • 30rd Symposium of the North-German Immunologists, Borstel, Germany (2007) “Towards understanding the role of species-specific microbiota during health and disease” Price for the Best Talk



12/2005 – 01/2009
Dissertation at the Christian-Albrechts University of Kiel, Zoological Institute, (supervised by Prof. Dr. Dr. h.c. Bosch) Title: Towards understanding a holobiont: Host-microbe interaction in Hydra; “summa cum laude”

1999 – 2005
Christian-Albrechts University Kiel, Germany
Diplom Biologie (Microbiology, Limnology, Toxicology) Diploma thesis: Bacterial symbionts in isopods (Crustacea: Isopoda): phylogenetic relationships and functional significance Final mark: 1.1

Work Experience

02/2013 – present
Independent junior research group leader at the Christian-Albrechts University of Kiel, Zoological Institute

02/2009 – 01/2013
Post-Doc at the Christian-Albrechts University of Kiel, Zoological Institute, group of Prof. Dr. Dr. h.c. Thomas Bosch

2012 – present
Assistant Project Manager for the laboratory of Prof. Bosch to work with genetically-modified organisms (S1)

Memberships in academic panels

7/2010 – present
elected member of the “Konvent der Math. Nat. Fakultät”; CAU Kiel

10/2012 – present
elected member in the „Sektionsausschuss Biologie“, CAU Kiel

Grants & Fellowships

Fraune2016 – 2019
HFSP Young Investigators’ Grant “Beyond the genome: impact of microbial communities and epigenetic regulations for adaptation” together with Adam Reitzel (USA) and Sylvain Forêt (Australia) (350.000 $)

logo-en2016 – 2019
SFB 1182 “Origin and Function of Metaorganisms” Co-PI in subproject A4 (291.600 €) and B1 (404.285 €)

2012 – 2015
DFG Einzelantrag FR 3041/2-1 „Host derived mechanisms controlling bacterial colonisation at the epithelial interface in the early branching metazoan Hydra” (263.496 €)

Travel grant to participate at the 2nd ASM Conference on Beneficial Microbes, San Diego (USA)

Scholarship Carl-Duisberg-Gesellschaft e.V. (ASA Program)
Ghana (5 month) Project: Goldmining – Effects on environment


Schnelle Anpassung an eine veränderliche Umwelt
Kieler Biologe erhält mit zwei internationalen Kollegen 900.000 Euro für Forschung. Einen stattlichen individuellen Förderungserfolg kann der Kieler Biologe Dr. Sebastian Fraune aus der Arbeitsgruppe Zell- und Entwicklungsbiologie der Christian-Albrechts-Universität zu Kiel (CAU) verbuchen.  link to KN newspaper article

Uralte Abwehr – Schon Nesseltiere nutzen Toll-ähnliche Rezeptoren als Mikroben-Detektor Auch der einfach gebaute Süßwasserpolyp Hydra besitzt bereits ein ausgeklügeltes Molekül-Arsenal, das fremde Invasoren in Schach hält. Die nur wenige Zentimeter großen Nesseltiere spüren Mikroorganismen genau wie Wirbeltiere über Toll-ähnliche Rezeptoren (TLR) auf, wie Kieler Zoologen um Thomas Bosch zeigten.

Lobor Journal online

Chemischer Schutzschild für Embryonen: Zwar verfügen Süßwasserpolypen nur über einen recht simplen Aufbau, dennoch erstaunen sie Biologen immer wieder. Kieler Wissenschaftler konnten nachweisen, dass sich die Embryonen der Tierchen mithilfe von antimikrobiellen Peptiden schützen. Eine Erkenntnis, die auch für den Menschen von Bedeutung sein könnte.

Deutschlandfunk (Tomma Schröder)

Nicht ohne meine Mikroben! Das Immunsystem muss gefährliche Keime auf Distanz halten. Aber zur effizienten Erfüllung dieser Aufgabe gehört, wie die Forschung immer deutlicher erkennen lässt, die guten Keime zu schonen und die Kommunikation mit einer Vielzahl von Bakterien zu organisieren.

FAZ (Karin Hollricher)