The genotoxic stress-inducible gene GEI1(Orf19.3109) is a repressor of virulence in Candida albicans

Ergosterol remodeling by the MARVEL protein Mrv6 links genotoxic stress adaptation to virulence in Candida albicans.

How fungal pathogens coordinate genotoxic stress responses with membrane homeostasis to sustain cellular signaling remains poorly understood. In this study, we characterize Mrv6, a MARVEL domain-containing membrane protein that is prominently induced by genotoxic stress. Intriguingly, rather than functioning as a canonical DNA repair factor, Mrv6 acts as a critical biophysical adjuster governing membrane lipid homeostasis. Deletion of MRV6 triggers a global transcriptional activation of the ergosterol biosynthetic pathway, resulting in aberrant cellular ergosterol accumulation. We demonstrate that this lipid imbalance fundamentally alters plasma membrane homeostasis, resulting in a less permeable architecture. Paradoxically, while this structural alteration inadvertently shields the fungus from exogenous genotoxins, conferring unexpected resistance to methyl methanesulfonate, it simultaneously hinders the intracellular transduction of environmental morphogenetic signals under hypoxic conditions. Consequently, the major hyphal repressor NRG1 remains aberrantly expressed, leading to an attenuated signaling response that significantly impairs virulence. Crucially, targeted genetic suppression of either the lipid biosynthetic node (ERG1) or the downstream signaling node (NRG1) effectively mitigates this biophysical constraint, rescuing both morphogenetic switching and pathogenicity. Collectively, our findings define a novel biochemical paradigm wherein C. albicans utilizes a stress-responsive membrane protein to fine-tune ergosterol remodeling and membrane permeability, structurally coupling stress adaptation to signal transduction.

The transcriptional regulator CasR controls mycobacterial antioxidant defense and biofilm formation via multiple direct targets.

AIMS The antioxidant defense system of Mycobacterium tuberculosis is critical for pathogenicity and persistence within macrophages, yet the regulatory networks remain poorly understood. This study aims to elucidate the molecular mechanism by which the transcription factor CasR regulates antioxidant defense in mycobacteria through delineation of the regulatory axis linking CasR activity, target gene expression, and the antioxidant phenotype. METHODS AND RESULTS Using Mycobacterium smegmatis as a model organism, we demonstrate that overexpression of CasR renders the bacteria significantly susceptible to hydrogen peroxide. Electrophoretic Mobility Shift Assay (EMSA) and β-galactosidase reporter analyses reveal that CasR directly binds and represses the promoter of cyp144, an uncharacterized cytochrome P450-encoding gene. Deletion of casRMsmreduces biofilm formation, consistent with the expected derepression of cyp144Msm, a gene that negatively regulates both biofilm and oxidative stress tolerance. EMSA and β-galactosidase activity assays also demonstrate that CasR negatively regulates antioxidant gene katGI, suggesting that CasR exerts a broader, global regulatory role within the mycobacterial antioxidant defense network. Furthermore, we identify isoleucine 18 as a critical residue for the DNA-binding and regulatory function of CasR. CONCLUSION This study establishes CasR as a pleiotropic transcriptional regulator that directly controls multiple antioxidant genes, including cyp144 and katGI, in mycobacteria. We report a previously unrecognized role for a cytochrome P450 family member in suppressing bacterial antioxidant capacity, as cyp144 overexpression reduces biofilm formation. These findings provide a valuable reference for further investigation into mycobacterial antioxidant mechanisms and identify CasR and Cyp144 as potential targets for the development of anti-tuberculosis drugs.

Oxidative stress induces E. coli aryl polyene expression, sensitizing the bacterial stress response and modulating the redox environment of innate immune cells

ABSTRACT Aryl polyenes (APEs) are specialized polyunsaturated outer membrane lipids that protect their producers from oxidative stress and contribute to biofilm formation. APEs are produced by an abundant biosynthetic gene cluster (BGC) family conserved across Gram-negative bacterial clades. The APE biosynthesis pathway involves 11 different enzymes and culminates in the attachment of APEs to an anchor molecule in the Gram-negative outer membrane. Unlike most other small molecule BGCs, the APE BGC does not contain a dedicated regulatory gene that controls the production of its metabolically costly compounds. Building from our prior observations of APEs’ role in acute oxidative stress protection, we use a uropathogenic Escherichia coli (UPEC) strain to show that APE expression conveys a potential competitive advantage characterized by increased early-stage growth, sensitization of the bacterial oxidative stress response, and dampening of the redox stress of innate immune cells after in vitro infection. Our data indicate that APEs could act as a UPEC fitness factor, and in future work, we aim to study their contribution to overall bacterial pathogenicity and survival, as well as how APEs could facilitate the transition from an oxygen-poor environment, such as the gut, to the oxygen-rich environment of the urinary tract. IMPORTANCE Bacterial pathogens use various mechanisms to achieve a competitive advantage under harsh conditions, such as during interactions with their host. We studied the function of aryl polyenes (APEs), specialized polyunsaturated fatty acids in the outer membrane, in the context of a uropathogenic E. coli strain. APE expression is induced by an oxidative environment and contributes to early-stage growth and sensitization of the oxidative stress response. Furthermore, APE-expressing E. coli dampen the intracellular oxidative milieu of target host phagocytes. These findings suggest a role for APEs as a fitness factor and create opportunities to study their in vivo function and explore them as a potential drug target. Bacterial pathogens use various mechanisms to achieve a competitive advantage under harsh conditions, such as during interactions with their host. We studied the function of aryl polyenes (APEs), specialized polyunsaturated fatty acids in the outer membrane, in the context of a uropathogenic E. coli strain. APE expression is induced by an oxidative environment and contributes to early-stage growth and sensitization of the oxidative stress response. Furthermore, APE-expressing E. coli dampen the intracellular oxidative milieu of target host phagocytes. These findings suggest a role for APEs as a fitness factor and create opportunities to study their in vivo function and explore them as a potential drug target.

The CRISPR/Cas-associated scaRNA modulates efeUOB expression and stress responses in Neisseria meningitidis

Abstract Neisseria meningitidis is a human-adapted commensal pathogen that must continuously balance nutrient acquisition with stress tolerance. Here, we identify a type II-C CRISPR/Cas-associated small RNA (scaRNA) as a posttranscriptional regulator of the efeUOB operon and oxidative stress responses. Using in vitro RNA binding and structure probing assays, we show that the scaRNA interacts with the 5′ untranslated region of efeO mRNA, leading to reduced translation of this component of the ferrous iron transporter EfeUOB. Consistent with this, efeO translational fusions demonstrate repression by the scaRNA, whereas a ΔscaRNA mutant shows increased reporter expression. We further show that meningococcal Cas9 (Nme1Cas9) is able to cleave scaRNA in vitro, but in vivo phenotypes are primarily scaRNA-dependent, indicating that Nme1Cas9 contributes, at most, indirectly to this regulation. In line with this observation, comparative proteomics revealed overlapping but distinct roles of scaRNA and Nme1Cas9 in oxidative stress adaptation, energy metabolism, and ion transport. While steady-state protein abundances did not capture all scaRNA-dependent effects, functional assays confirmed that scaRNA inactivation reduces survival under oxidative stress. Together, our results identify scaRNA-mediated repression of efeO as a novel posttranscriptional mechanism that contributes to stress adaptation in meningococci. These findings expand the functional repertoire of CRISPR-associated elements and suggest a role for small RNA-based regulation in iron-related stress adaptation in a major human pathogen.

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Dual regulatory roles of the zinc cluster transcription factor MrFTRP1 in development, stress tolerance, and virulence of Metarhizium robertsii.

It is demonstrated that MrFTRP1 exerts a dual-regulatory functioning as a positive regulator of conidiation and pathogenesis but a negative regulator of environmental stress tolerance, which expands the understanding of the regulatory diversity within the C6 TF family and identifies him as a promising target for the genetic improvement of mycoinsecticides.