Specificity and diversity of fungal-bacterial interactions
Norio TAKESHITA
University of Tsukuba, Faculty of Life and Environmental Sciences,
Microbiology Research Center for Sustainability(MiCS)
Report: Exclusivity in physical spaces and nutrients is a prerequisite for the survival oforganisms, but a few species have been able to develop mutually beneficial strategies thatallow them to co-habit. We discovered a mutualistic mechanism between the filamentous
fungus, Aspergillus nidulans and the bacterium, Bacillus subtilis (Abeysinghe et al 2020). The
bacterial cells co-cultured with the fungus traveled along the mycelia using their flagella anddispersed farther with the expansion of the fungal colony, indicating that the fungal mycelia
supply space for the bacteria to migrate, disperse and proliferate. Transcriptomic, genetic,
molecular mass and imaging analyses demonstrated that the bacteria reached the mycelial edge
and supplied thiamine to the growing hyphae, which led to a promotion of hyphal growth. The
transfer of thiamine from bacteria to the thiamine non-auxotrophic fungus was directlydemonstrated by stable isotope labeling. The simultaneous spatial and metabolic interactions
reveal a mutualism that facilitates the communicating fungal and bacterial species to obtain anenvironmental niche and nutrient, respectively.
Research objectives
Bacteria and fungi comprise a large fraction of the biomass in soil. Since they interact witheach other to carry out their characteristic functions in the ecosystem, a better knowledge ofbacterial-fungal interactions is important to understand the microbial ecosystem, which isclosely related to agriculture, medicine, and the environment. This project aimed to reveal theinter-kingdom interactions through diverse factors such as antibiotics, signaling molecules,cooperative metabolism, and physical interactions.
Methods
We co-cultured a model filamentous fungus, Aspergillus nidulans and the bacterium, Bacillus
subtilis on agar plates. Their spatial and metabolic interactions were analyzed throughtranscriptome, genetic, molecular mass and imaging analyses.
Results
The bacterial cells co-cultured with the fungus travel along the mycelia depending on theirflagella and disperse with the expansion of the fungal colony, indicating that the fungal

mycelia supply space for bacteria to migrate, disperse and proliferate. Transcriptome, genetic,
molecular mass and imaging analyses demonstrate that the bacteria reach the mycelial edge
and supply thiamine to the growing hyphae, resulting in a promotion of hyphal growth. The
transfer of thiamine from the bacteria to the thiamine non-auxotrophic fungus is directly
demonstrated by stable isotope labeling.
Conclusion
The simultaneous spatial and metabolic interactions reveal a mutualism that facilitates thecommunicating fungal and bacterial species to obtain an environmental niche and nutrient,
respectively.
References
Abeysinghe, G., Kuchira, M., Kudo, G., Masuo, S., Ninomiya, A., Takahashi, K., Utada, A.
S., Hagiwara, D., Nomura, N., Takaya, N., Obana, N., Takeshita, N. (2020) Fungal mycelia
and bacterial thiamine establish a mutualistic growth mechanism. Life Science Alliance. 3, 12,e202000878. DOI: 10.26508/lsa.202000878