Microfluidics Reveals Trapping of Endosymbiotic Bacteria Inside a Fungus

Ingrid Richter^a, Zerrin Uzum^a, Calire Stanley^b, Sacha Pidot^c, Christian Hertweck^a^,^d

^aDepartment of Biomolecular Chemistry, Leibniz Institute for Natural Product Research and Infection Biology, Jena, Germany, Beutenbergstraße, 11A, Jena, Germany

^bDepartment of Bioengineering, Imperial College London, London, UK, South Kensington Campus, London, United Kingdom

^cDepartment of Microbiology and Immunology at the Doherty Institute for Infection and Immunity, University of Melbourne, Melbourne, Australia, The University of Melbourne Grattan Street, Parkville, Victoria, Australia

^dFaculty of Biological Sciences, Friedrich Schiller University Jena, Jena, Germany, Bachstraße 18k, Jena, Germany

Proceedings of Emerging Investigators in Microfluidics Conference (EIMC)

Online, Spain, 2021 July 20th - October 6th

Organizers: Adrian Nightingale, Darius Rackus and Claire Stanley

Oral, Ingrid Richter, presentation 025
DOI: https://doi.org/10.29363/nanoge.eimc.2021.025
Publication date: 5th July 2021

Fungal-bacterial interactions (BFIs) are highly prevalent in nature and are critically important in a variety of fields such as agriculture, biotechnology, and medicine [1]. An important feature of BFIs is the ability of bacteria to control and exploit their eukaryotic hosts [2]. The most intriguing case of bacteria controlling host reproduction is the endosymbiosis between the zygomycete Rhizopus microsporus and its bacterial endosymbiont Burkholderia rhizoxinica [3, 4]. In this agriculturally relevant symbiosis [5], host reproduction through spores relies exclusively on the presence of endobacteria [4]. However, there is a considerable lack of knowledge about the molecular basis of this interaction. Through a combination of genomic and functional studies, we show that B. rhizoxinica transcription activator-like effectors (BATs) are essential for the establishment of a stable symbiosis. Utilising novel microfluidics devices [6] in combination with fluorescence microscopy we report induction of septa biogenesis in R. microsporus. This leads to trapping of BAT-deficient endobacteria in infected hyphae. Considering that the survival rate of trapped bacteria is significantly reduced, endosymbionts incapable of secreting BAT proteins may elicit a protective response from the fungus. The occurrence of septa is one of the most surprising results, as Zygomycetes generally lack septate hyphae. The impact of endobacteria on fungal physiology offers a broader view on the dynamic interactions between bacteria and fungi.

1. Frey-Klett, P., et al., Bacterial-fungal interactions: hyphens between agricultural, clinical, environmental, and food microbiologists. Microbiology and Molecular Biology Reviews, 2011. 75(4): p. 583-609.

2. Dale, C. and N.A. Moran, Molecular interactions between bacterial symbionts and their hosts. Cell, 2006. 126(3): p. 453-465.

3. Partida-Martinez, L.P. and C. Hertweck, Pathogenic fungus harbours endosymbiotic bacteria for toxin production. Nature, 2005. 437(7060): p. 884-888.

4. Partida-Martinez, L.P., et al., Endosymbiont-dependent host reproduction maintains bacterial-fungal mutualism. Curr Biol, 2007. 17(9): p. 773-777.

5. Scherlach, K., et al., Symbiotic cooperation in the biosynthesis of a phytotoxin. Angew Chem Int Ed Engl., 2012. 51(38): p. 9615-9618.

6. Stanley, C.E., et al., Probing bacterial-fungal interactions at the single cell level. Integr Biol, 2014. 6(10): p. 935-945.

References:

[1] Frey-Klett, P., et al., Bacterial-fungal interactions: hyphens between agricultural, clinical, environmental, and food microbiologists. Microbiology and Molecular Biology Reviews, 2011. 75(4): p. 583-609

[2] Dale, C. and N.A. Moran, Molecular interactions between bacterial symbionts and their hosts. Cell, 2006. 126(3): p. 453-465.

[3] Partida-Martinez, L.P. and C. Hertweck, Pathogenic fungus harbours endosymbiotic bacteria for toxin production. Nature, 2005. 437(7060): p. 884-888.

[4] Partida-Martinez, L.P., et al., Endosymbiont-dependent host reproduction maintains bacterial-fungal mutualism. Curr Biol, 2007. 17(9): p. 773-777.

[5] Scherlach, K., et al., Symbiotic cooperation in the biosynthesis of a phytotoxin. Angew Chem Int Ed Engl., 2012. 51(38): p. 9615-9618.

[6] Stanley, C.E., et al., Probing bacterial-fungal interactions at the single cell level. Integr Biol, 2014. 6(10): p. 935-945.

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