Long Lin, Zhiyuan Zhang, Hongda Fang, Yicheng Yang, Xiuyuan Li, Han Chen, Min Tao, Yuhan Dong, Bingxin Wang, Danyu Shen, Xiaolong Shao, Limin Wang, Jinshui Zheng, Mengcen Wang, Fengquan Liu, Guoliang Qian
Interkingdom competition between bacteria and fungi in nutrient-limited environments drives microbial community dynamics, yet the molecular mechanisms enabling bacterial dominance during bacterial-fungal interaction remain poorly characterized. This study reveals a paradigm-shifting role for bacterial type IV secretion system (T4SS) by demonstrating that a specialized bacterial-killing T4SS (T4SSBK) in Lysobacter enzymogenes serves as a universal cross-kingdom antifungal weapon. Combining genetic, biochemical, and bioinformatical approaches, we show that T4SSBK mediates direct contact-dependent suppression of phylogenetically diverse fungi-including unicellular yeasts and filamentous species-through delivery of a conserved deoxyribonuclease effector, LtdD. Structural characterization reveals that LtdD homologs are evolutionarily conserved across T4SSBK-harboring bacterial lineages, suggesting widespread ecological deployment of this antifungal strategy. These findings overturn the classical dogma of T4SSBK as an antibacterial apparatus and establish it as a multifunctional microbial combat system capable of trans-kingdom interference. By elucidating a DNA-targeting mechanism of fungal growth inhibition, our work not only redefines the ecological role of T4SSBK in microbial warfare but also provides a molecular blueprint for engineering DNA-based antifungal therapies.