Yigit, K. | Search bioRxiv

bioRxiv2026

Collateral consequences of oxidative stress responses result in mitomycin C sensitivity

Bacterial survival depends on carefully balanced antioxidant defenses against reactive oxygen species. Caulobacter crescentus employs the transcription factor OxyR to activate hydrogen peroxide detoxification genes, a seemingly straightforward protective strategy. Here, we reveal an unexpected consequence of environment or genetic activation of peroxide resistance via OxyR resulting in vulnerability to reductively activated antibiotics. An activated OxyR allele protects against peroxide stress due to upregulation of the catalase-peroxidase KatG but simultaneous induction of the AhpCF reductase sensitizes cells to the reductively activated genotoxin mitomycin C. We show that this collateral vulnerability can be induced by brief exposure to oxidative stress and extends to bacteria beyond Caulobacter. Our findings illuminate a hidden cost of antioxidant signaling as robust defense against oxidative stress paradoxically creates exploitable vulnerabilities to chemotherapeutic prodrugs. SIGNIFICANCECellular stress responses are vital for survival, but our work reveals an underappreciated principle where activation creates trade-offs with far-reaching consequences. Using Caulobacter crescentus, we show that strengthened antioxidant defenses against peroxide simultaneously increase vulnerability to mitomycin C. Because these regulatory mechanisms are widespread across bacteria, our findings suggest a general model wherein stress-defense pathways unavoidably compromise resistance to alternative threats. This conceptual framework not only advances our understanding of stress-response regulation but also identifies new strategies for therapeutic exploitation of bacterial vulnerabilities.

microbiology↗

bioRxiv2024

Proteolytic control of FixT by the Lon protease impacts FixLJ signaling in Caulobacter crescentus

Responding to changes in oxygen levels is critical for aerobic microbes. In Caulobacter crescentus, low oxygen is sensed by the FixL-FixJ two-component system which induces multiple genes, including heme biosynthesis, to accommodate microaerobic conditions. The FixLJ inhibitor FixT is also induced under low oxygen conditions and is degraded by the Lon protease, which together provides negative feedback proposed to adjust FixLJ signaling thresholds during changing conditions. Here, we address if the degradation of FixT by the Lon protease contributes to phenotypic defects associated with loss of Lon. We find that {Delta}lon strains are deficient in FixLJ-dependent heme biosynthesis, consistent with elevated FixT levels as deletion of fixT suppresses this defect. Transcriptomics validate this result as there is diminished expression of many FixLJ-activated genes in {Delta}lon. However, no physiological changes in response to microaerobic conditions occurred upon loss of Lon, suggesting that FixT dynamics are not a major contributor to fitness in oxygen limiting conditions. Similarly, stabilization of FixT in {Delta}lon strains does not contribute to any known Lon-related fitness defect, such as cell morphology defects or stress sensitivity. In fact, cells lacking both FixT and Lon are compromised in viability during adaptation to long term aerobic growth. Our work highlights the complexity of protease-dependent regulation of transcription factors and explains the molecular basis of defective heme accumulation in Lon-deficient Caulobacter. ImportanceThe Lon protease shapes protein quality control, signaling pathways, and stress responses in many bacteria species. Loss of Lon often results in multiple phenotypic consequences. In this work, we found a connection between the Lon protease and deficiencies in heme accumulation that then led to our finding of a global change in gene expression due to degradation of a regulator of the hypoxic response. However, loss of degradation of this regulator did not explain other phenotypes associated with Lon deficiencies demonstrating the complex and multiple pathways that this highly conserved protease can impact.

microbiology↗