A fungal pH-responsive signaling pathway regulating Aspergillus adaptation and invasion into the cornea.
OBJECTIVE
To investigate the role of PalB and PacC, two components of a pH-responsive signal-transduction pathway of Aspergillus nidulans, during the pathogenesis of fungal infection of the cornea.


METHODS
Fungal strains included an A. nidulans wild-type isolate (A83), loss-of-function A. nidulans mutants of the palB (B7) or pacC (C6309) genes, and reconstituted genotypic strains (B7R and C6309R). Doubling times and radial growth rates were examined under neutral and acidic conditions. Corneal virulence was assessed ex vivo by topical inoculation of scarified porcine or human corneas with A. nidulans strains maintained in buffered medium until histologic examination after days 1, 3, and 5.


RESULTS
In vitro growth kinetics were similar for A. nidulans strains in liquid medium at pH 6.0 (P = 0.24) and 7.3 (P = 0.75). The pacC mutant C6309 grew more slowly (P < 0.001) on solid medium, whereas palB and pacC rescuants had growth kinetics comparable to those of the wild-type. Wild-type A. nidulans germinated on porcine corneas and produced hyphae that progressively invaded the stroma, reaching an average maximum penetration of 56% +/- 9% at 5 days after exposure. In contrast, hyphal invasion was significantly less by mutant strains B7 (P = 0.005) and C6309 (P = 0.003). Fungal penetration by C6309 was also significantly less than the wild-type (P = 0.0005) on explanted human corneas. Both fungal rescuants showed stromal invasion similar to the wild-type.


CONCLUSIONS
Corneal invasion by filamentous hyphae is attenuated by palB and pacC mutant strains of A. nidulans. The PacC pathway is involved in regulating fungal filamentation during ex vivo Aspergillus infection of the cornea.
Hua
Xia
X
Sid W Richardson Ocular Microbiology Laboratory, Department of Ophthalmology, Cullen Eye Institute, Baylor College of Medicine, Houston, Texas 77030, USA.
Yuan
Xiaoyong
X
Wilhelmus
Kirk R
KR
D000818:Animals; D001228:Aspergillosis / Q000382:microbiology*; D001233:Aspergillus nidulans / Q000235:genetics / Q000472:pathogenicity*; D003320:Corneal Ulcer / Q000382:microbiology*; D003546:Cysteine Endopeptidases / Q000502:physiology*; D015821:Eye Infections, Fungal / Q000382:microbiology*; D005656:Fungal Proteins / Q000502:physiology*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D015398:Signal Transduction / Q000502:physiology*; D013552:Swine; D014157:Transcription Factors / Q000502:physiology*; D014774:Virulence; D016335:Zinc Fingers / Q000502:physiology
D005656:Fungal Proteins; C092394:PacC protein, Aspergillus; D014157:Transcription Factors; D003546:Cysteine Endopeptidases; C097042:PalB protein, Aspergillus nidulans