Secretion Systems Used by Bacteria to Counteract Fungal Competitors

Although bacterial secretion systems (BSSs) are well known to mediate antifungal effects, current evidence remains fragmented, and a framework linking antifungal strategies in bacterial–fungal warfare is still absent. In this context, we survey Type I to XI secretion systems, integrating experimentally validated activities with mechanism-based predictions of antifungal potential. On this basis, we highlight that the antifungal activity of BSSs operates through two different layers: direct fungicidal attack, via effector-mediated disruption of fungal cellular integrity, and ecological competition, through nutrient competition, physical niche occupation, and coordinated population-level activities. Nevertheless, the mechanistic understanding of bacterial antifungal strategies remains limited by simplified experimental models, incomplete effector repertoires, and poorly characterized regulatory networks and environmental cues. Addressing these gaps will require integrated experimental models, advanced high-throughput platforms, and comprehensive multi-omics-guided analyses to elucidate how bacteria suppress fungi and to support future applications. In addition, BSSs represent versatile and programmable platforms for the development of sustainable antifungal interventions in both agricultural and biomedical settings.