A. LOHBERGER (1,3 - AFFILATION NUMBERS)¹, JE SPANGENBERG², Y VENTURA¹, N JEANNERET¹, K JEANNERET¹, S BINDSCHEDLER¹, R BSHARY⁴, E VERRECCHIA³, P JUNIER<sup>1

1</sup>Laboratory of Microbiology, Institute of Biology, University of Neuchâtel. Rue Emile-Argand 11, 2000, Neuchâtel, Switzerland, ²Institute of Earth Surface Dynamics, University of Lausanne, Géopolis, 1015 Lausanne, Switzerland, ³Laboratory of Biogeosciences, Institute of Earth Sciences, University of Lausanne. Géopolis, 1015 Lausanne, Switzerland, ⁴Laboratory of Eco-ethology, Institute of Biology, University of Neuchâtel. Rue Emile-Argand 11, 2000, Neuchâtel, Switzerland

Fungi and bacteria have a long co-evolutionary history in terrestrial ecosystems. In soils, they are the basis for nutrient recycling. Therefore, not only do they co-exist, but they are also potential competitors for resources. In our laboratory, it was shown that the bacterium Pseudomonas putida benefits from the interaction with fungi by using the so-called “Fungal Highways” to disperse in porous unsaturated soil-like media. Dispersal allows this bacterium to reach inaccessible nutrient sources, as its mobility is limited in soil-like conditions (1, 2). However, the direct fitness benefit for the fungi remains unknown. Until now, a long-term benefit was shown for the fungus Morchella crassipes, which acted as a farmer of the dispersing bacteria and stored bacterial carbon into resting structures (2). However the role of other trophic exchange mechanisms favouring fungal highways remains unknown. In terms of organic nitrogen exploitation we have determined that fungal proteolysis can be enhanced by dispersal of P. putida and this is not the result of direct competition as it occurs even when fungal cells are removed, but living bacterial cells are required. We tested if a mutual benefit was dependent on a given nitrogen/carbon (N/C) ratio. When organic nitrogen and carbon, or just the former, were highly available, bacteria were not farmed by the fungi and thus benefited from dispersal and nutrient acquisition. The fungus also gained from the interaction when nitrogen and carbon were highly available, but when the C/N ratio was higher, fungal biomass decreased. Our results show that the sharing of the benefits of fungal-driven bacterial dispersal is strongly context-dependent and that nutrient acquisition might be the driving factor of this type of bacteria-fungi interaction.


1. Pion M, Bshary R, Bindschedler S, Filippidou S, Wick LY, et al. Gains of bacterial flagellar motility in a fungal world. Applied and Environmental Microbiology. 2013 Nov;79(22):6862-7. PubMed PMID: 23995942. Pubmed Central PMCID: 3811526.
2. Pion M, Spangenberg JE, Simon A, Bindschedler S, Flury C, et al. Bacterial farming by the fungus Morchella crassipes2013 2013-12-22 00:00:00.