Activation of an antifungal pathway in Yersinia pseudotuberculosis by chitin-receptor-mediated fungal recognition.

Despite the ubiquitous nature of bacterial-fungal interactions (BFIs), it is not fully understood how bacteria detect the presence of a potential fungal competitor to initiate appropriate defense responses. In this study, we show that the enteropathogen Yersinia pseudotuberculosis (Yptb) utilizes the two-component system (TCS) histidine kinase RstB to sense chitin as a pathogen-associated molecular pattern (PAMP) for detecting fungi, resulting in the phosphorylation of the downstream response regulator RstA and subsequent activation of the classical type II secretion system (T2SS) and the tight adherence secretion system (TadSS), a major subtype of T2SS. The activation of T2SS and TadSS facilitates the secretion of chitinase T2SS/TadSS-related chitinase effector (TscE), which eliminates fungi and enhances bacterial colonization of the murine gut. These findings not only elucidate the role of T2SS and TscE in antagonizing fungal competitors but also offer insights into the interkingdom recognition mechanisms between bacteria and fungi.