A molecular switch: antitoxin HigA integrates transcriptional activation by XreR and proteolytic clearance by Lon to balance virulence and stress adaptation in the fish pathogen Edwardsiella piscicida

Abstract

Toxin-antitoxin (TA) systems are pivotal in the bacterial stress response, yet signals controlling their activation and functional integration into virulence remain poorly understood. This study unveils a multi-layered signaling network centered on antitoxin HigA in the fish pathogen Edwardsiella piscicida. We identify XreR, a novel XRE-family transcriptional regulator, as a direct transcriptional activator of higA, and demonstrate that XreR-dependent upregulation of HigA modulates virulence. Beyond its antitoxin function, HigA acts as a transcription factor that directly activates ethB, a hemolysin activator gene, thereby enhancing hemolysis. However, excessive hemolysis triggers a host pyroptosis-like response, compromising intramacrophage survival and revealing a dual role for EthB in virulence. Based on the hypersensitivity of xreROE to oxidative stress, we reveal that HigA attenuates oxidative stress tolerance by directly repressing the RpoS-KatG pathway. This repression is counterbalanced by Lon protease, which degrades HigA under oxidative stress, representing a critical post-translational negative regulatory mechanism. Collectively, our findings establish the XreR-HigA-Lon axis as a central regulatory module. This not only governs hemolytic virulence via the XreR-HigA-EthB pathway but also mediates oxidative tolerance through the Lon-HigA-RpoS-KatG pathway, thereby revealing the dual role of HigA in coordinating pathogenicity and stress adaptation. This study offers a new paradigm for understanding how bacterial pathogens balance infection progression with host environmental constraints.

Keywords

HigA / Hemolysis / Oxidative tolerance / Virulence / Regulatory pathway / Edwardsiella piscicida

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The Author(s), under exclusive licence to Ocean University of China