Assessing the specificity of bacterial-fungal interactions for biocontrol strategies

Fungal-bacterial interactions and their applications are gaining increasing attention in various fields, including biocontrol technologies. Numerous studies have examined these interactions, typically involving only a single fungal isolate and a limited number of bacterial isolates. We hypothesized that even a modest increase in the number of isolates included in confrontation experiments would reveal patterns of functional relevance and possible specificity in fungal-bacterial interactions.

This study included four microfungal isolates from soil and thirteen bacterial isolates from macrofungal fruiting bodies for confrontation experiments. Both the fungus and the bacterium influence their interactions, though the fungus appears slightly more selective. For instance, certain fungal isolates from the genera Colletotrichum and Phoma sensu lato (s.l.) responded more strongly to the presence of bacteria than those from the genera Cadophora and Microdochium. However, the responses of Microdochium and Phoma s.l. were not dependent on the bacterial genus or isolate used in confrontation experiments. Notably, a single bacterial genus consistently suppressed multiple fungal genera, suggesting potential off-target effects if used for biocontrol. The results further showed that the influence of bacteria on fungal growth was more pronounced at the bacterial isolate than the genus level, indicating considerable variability within the same genus.

Using more bacterial and fungal isolates in confrontation experiments clarifies the drivers of interactions, fungal responses, and bacterial off-target effects. The research presented here highlights the need for further systematic, in-depth research into fungal-bacterial interactions to validate existing findings, establish a traceable, easily analyzable isolate-level dataset, and prevent unintended consequences in microbial biocontrol applications and beyond.