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       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  (see Pietschke C et al 2017)
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 Fraune et al. 2016)
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




  • Hamada, M, Schröder, K, Kürn, U, Fraune S, Khalturina M, Shinzato C, Satoh N, Bosch TCG Metabolic co-dependence drives the evolutionarily ancient Hydra-Chlorella symbiosis eLife (in press)
  • Domin H, Zurita-Gutiérrez YH, Scotti M, Buttlar J, Hentschel Humeida U, Fraune S (2018). Predicted bacterial interactions affect in vivo microbial colonization dynamics in Nematostella Front Microbiol, 9, 728, https://doi.org/10.3389/fmicb.2018.00728
  • Mortzfeld BM, Taubenheim J, Fraune S, Klimovich AV, Bosch TCG (2018). Stem cell transcription factor FoxO controls microbiome resilience in Hydra. Front Microbiol., https://doi.org/10.3389/fmicb.2018.00629
  • Wein T, Dagan T, Fraune S, Bosch TCG, Reusch TB, Hülter NF (2018) Priority rules in microbiota colonization dynamics Front Microbiol., 9 DOI 10.3389/fmicb.2018.00443
  • Bang C, Dagan T, Deines P, Dubilier N, Duschl WJ, Fraune S, Hentschel U, Hirt H, Hülter N, Lachnit T, Picazo D, Pita L, Pogoreutz C, Radecker N, Saad MM, Schmitz RA, Schulenburg H, Voolstra CR, Weiland-Brauer N, Ziegler M, Bosch TCG (2018). Metaorganisms in extreme environments: do microbes play a role in organismal adaptation? Zoology, 15, 2018. https://doi.org/10.1016/j.zool.2018.02.004
  • Li XY, Lachnit T, Fraune S, Bosch TCG,Traulsen A, Sieber M (2017) Temperate phages as self-replicating weapons in bacterial competition. R. Soc. Interface, 14(137), doi: 10.1098/rsif.2017.0563
  • Pietschke C, Treitz C, Forêt S, Schultze A, Künzel S, Tholey A, Bosch TCG, Fraune S (2017) Host modification of a bacterial quorum sensing signal induces a phenotypic switch in bacterial symbionts. Proc Natl Acad Sci USA, 114(40):E8488-E8497
  • Augustin R, Schröder K, Murillo Rincón AP, Fraune S, Anton-Erxleben F, Herbst E-M, Wittlieb J, Schwentner M, Grötzinger J, Wassenaar TM, Bosch TCG (2017) A secreted antibacterial neuropeptide shapes the microbiome in Hydra. Nature Comm., 8(1):69
  • Pita L, Fraune S, Hentschel U (2016) Emerging sponge models of animal-microbe symbioses, Frontiers in Microbiology 7, 2102. doi: 10.3389/fmicb.2016.02102
  • Fraune S, Forét S, Reitzel AM (2016) Using Nematostella vectensis to study the interactions between genome, epigenome, and bacteria in a changing environment, Frontiers in Marine Science 3, 148, doi: 10.3389/fmars.2016.00148
  • 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


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)