A bacterial chaperone-usher pathway links interkingdom association to antimicrobial protection of a fungal partner
Abstract
Antimicrobial compounds (AMCs) influence species-level composition of microbial communities, governing beneficial and pathogenic interactions with plant and mammalian hosts. Phenazine-1- carboxylic acid (PCA) is a bacterially produced, redox-active AMC abundant in the rhizosphere. A recent study discovered the PCA-susceptible fungus Aspergillus calidoustus can grow in PCA- abundant environments by associating with phenazine-tolerant bacteria, including the novel species Paraburkholderia edwinii . P. edwinii’s protection response is characterized by adherence to its fungal partner, bacterial aggregation, and sequestration and reduction of PCA, rendering PCA less toxic. Deletion of the bacterial transcriptional repressor HrcA generates a constitutively active protection response and enhanced protection of A. calidoustus . Here, we use the Δ hrcA strain to determine whether fungal protection uses bacterial self-protection machinery or dedicated interkingdom mechanisms. We identified a divergent archaic chaperone–usher pathway (CUP) operon encoding a predicted periplasmic chaperone, outer membrane usher, putative major pilin-like subunit, and putative adhesin-like tip protein. While many archaic CUP operons are annotated in diverse bacteria, their functions remain largely unexplored. We show these f ungal a ttachment c omplex ( fac ) genes promote bacterial-fungal attachment, are required for P. edwinii to sequester and detoxify PCA, and contribute to full fungal protection from PCA stress, despite not being required for P. edwinii ’s own tolerance of PCA. We further identified the transcription regulator, FacR, that influences expression of the fac system. Understanding the functions of divergent archaic CUP systems may illuminate protective interkingdom partnerships and inform how pathogenic and beneficial microbes gain entry to AMC-replete environments, shaping microbial communities in agricultural and clinical contexts.
IMPORTANCE: Some species of fungi can be opportunistic pathogens, while others promote rhizosphere stability. Antimicrobial compounds help govern the composition of microbial communities by excluding susceptible organisms and selecting for microbes with intrinsic resistance. However, susceptible fungi can gain entry into microbial communities containing antagonist compounds by partnering with protective bacteria, and it is unknown whether bacteria are extending the mechanisms of self-tolerance to fungal partners, or if there is dedicated machinery for interkingdom protection. Here, we show that Paraburkholderia edwinii uses a divergent chaperone–usher system to associate with its fungal partner, Aspergillus calidoustus , and protect it from phenazine stress. This system promotes fungal attachment, antimicrobial sequestration, and maintenance of a reducing environment, yet is dispensable for the bacterium’s own survival. These findings demonstrate that bacteria can deploy dedicated machinery to protect partners across kingdoms, revealing that antimicrobial tolerance can emerge from microbial interactions rather than intrinsic resistance alone.
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BibTeX
@misc{gonzalez2026bacterial,
title = {{A bacterial chaperone-usher pathway links interkingdom association to antimicrobial protection of a fungal partner}},
author = {Alyssia Gonzalez and Kurt Dahlstrom},
howpublished = {bioRxiv},
year = {2026},
month = oct,
doi = {10.64898/2026.10.29.762636},
url = {https://www.biorxiv.org/content/10.64898/2026.10.29.762636v1},
note = {CC BY-NC},
}
RIS
TY - UNPB
TI - A bacterial chaperone-usher pathway links interkingdom association to antimicrobial protection of a fungal partner
AU - Alyssia Gonzalez
AU - Kurt Dahlstrom
PY - 2026
DA - 2026/10/29
PB - bioRxiv
DO - 10.64898/2026.10.29.762636
UR - https://www.biorxiv.org/content/10.64898/2026.10.29.762636v1
AB - Antimicrobial compounds (AMCs) influence species-level composition of microbial communities, governing beneficial and pathogenic interactions with plant and mammalian hosts. Phenazine-1- carboxylic acid (PCA) is a bacterially produced, redox-active AMC abundant in the rhizosphere. A recent study discovered the PCA-susceptible fungus Aspergillus calidoustus can grow in PCA- abundant environments by associating with phenazine-tolerant bacteria, including the novel species Paraburkholderia edwinii . P. edwinii’s protection response is characterized by adherence to its fungal partner, bacterial aggregation, and sequestration and reduction of PCA, rendering PCA less toxic. Deletion of the bacterial transcriptional repressor HrcA generates a constitutively active protection response and enhanced protection of A. calidoustus . Here, we use the Δ hrcA strain to determine whether fungal protection uses bacterial self-protection machinery or dedicated interkingdom mechanisms. We identified a divergent archaic chaperone–usher pathway (CUP) operon encoding a predicted periplasmic chaperone, outer membrane usher, putative major pilin-like subunit, and putative adhesin-like tip protein. While many archaic CUP operons are annotated in diverse bacteria, their functions remain largely unexplored. We show these f ungal a ttachment c omplex ( fac ) genes promote bacterial-fungal attachment, are required for P. edwinii to sequester and detoxify PCA, and contribute to full fungal protection from PCA stress, despite not being required for P. edwinii ’s own tolerance of PCA. We further identified the transcription regulator, FacR, that influences expression of the fac system. Understanding the functions of divergent archaic CUP systems may illuminate protective interkingdom partnerships and inform how pathogenic and beneficial microbes gain entry to AMC-replete environments, shaping microbial communities in agricultural and clinical contexts. IMPORTANCE: Some species of fungi can be opportunistic pathogens, while others promote rhizosphere stability. Antimicrobial compounds help govern the composition of microbial communities by excluding susceptible organisms and selecting for microbes with intrinsic resistance. However, susceptible fungi can gain entry into microbial communities containing antagonist compounds by partnering with protective bacteria, and it is unknown whether bacteria are extending the mechanisms of self-tolerance to fungal partners, or if there is dedicated machinery for interkingdom protection. Here, we show that Paraburkholderia edwinii uses a divergent chaperone–usher system to associate with its fungal partner, Aspergillus calidoustus , and protect it from phenazine stress. This system promotes fungal attachment, antimicrobial sequestration, and maintenance of a reducing environment, yet is dispensable for the bacterium’s own survival. These findings demonstrate that bacteria can deploy dedicated machinery to protect partners across kingdoms, revealing that antimicrobial tolerance can emerge from microbial interactions rather than intrinsic resistance alone.
SN - 2692-8205
ER -