Role of laeA in the Regulation of alb1 , gliP , Conidial Morphology, and Virulence in Aspergillus fumigatus

Abstract

The alb1 (pksP) gene has been reported as a virulence factor controlling the pigmentation and morphology of conidia in Aspergillus fumigatus. A recent report suggested that laeA regulates alb1 expression and conidial morphology but not pigmentation in the A. fumigatus strain AF293. laeA has also been reported to regulate the synthesis of secondary metabolites, such as gliotoxin. We compared the role of laeA in the regulation of conidial morphology and the expression of alb1 and gliP in strains B-5233 and AF293, which differ in colony morphology and nutritional requirements. Deletion of laeA did not affect conidial morphology or pigmentation in these strains, suggesting that laeA is not involved in alb1 regulation during conidial morphogenesis. Deletion of laeA, however, caused down-regulation of alb1 during mycelial growth in a liquid medium. Transcription of gliP, involved in the synthesis of gliotoxin, was drastically reduced in B-5233laeA⌬, and the gliotoxin level found in the culture filtrates was 20% of wild-type concentrations. While up-regulation of gliP in AF293 was comparable to that in B-5233, the relative mRNA level in AF293laeA⌬ was about fourfold lower than that in B-5233laeA⌬. Strain B-5233laeA⌬ caused slower onset of fatal infection in mice relative to that with B-5233. Histopathology of sections from lungs of infected mice corroborated the survival data. Culture filtrates from B-5233laeA⌬ caused reduced death in thymoma cells and were less inhibitory to a respiratory burst of neutrophils than culture filtrates from B-5233. Our results suggest that while laeA is not involved in the regulation of alb1 function in conidial morphology, it regulates the synthesis of gliotoxin and the virulence of A. fumigatus.Aspergillus fumigatus, a ubiquitous saprophyte, is the predominant cause of aspergillosis throughout the world. This species most often causes life-threatening invasive aspergillosis (IA) in individuals with dysfunctional phagocytes or with prolonged neutropenia resulting from immunosuppressive drug therapy (9,19). In previous studies, we have dissected the molecular basis of conidial pigment formation and identified a cluster of six genes involved in the biosynthesis of dihydroxynaphthalene (DHN)-like melanin in A. fumigatus strain B-5233 (34-37). The alb1 (pksP) gene in this cluster encodes a polyketide synthase that catalyzes the first step of DHN-like melanin synthesis during conidial formation. Conidia of A. fumigatus are bluish green and coarsely echinulated due to the protrusions on their surfaces as revealed by scanning electron microscopy (34). Deletion of the alb1 gene from strain B-5233 resulted in two simultaneous changes in conidial morphology: albino instead of bluish green color and a smooth rather than echinulated surface. Complementation of the alb1⌬ strain with the wild-type alb1 gene restored the bluish green pigment as well as the echinulation on the surface (17, 34), indicating that the alb1 gene is involved in conidial morphology as well as in conidial pigment synthesis. Fur...

Reduced Nicotinamide Adenine Dinucleotide Phosphate Oxidase-Independent Resistance to Aspergillus fumigatus in Alveolar Macrophages

“…In fact, the presence of a five-fold excess of conidia abolished all SOD-inhibitable NADPH oxidase activity in adherent AM. It is not known if this result is related to the reduced oxidant production from PMN following exposure to A. fumigatus hyphal culture filtrates (79). Additional studies are therefore required to better understand the mechanism by which conidia influence the luminometry signal resulting from superoxide produced by these phagocytes.…”

Extrapulmonary Aspergillus infection in patients with CARD9 deficiency

“…Two clinical strains of A. fumigatus obtained from patients with invasive pulmonary aspergillosis were used for neutrophil functional assays in patient 1 (Sq-001) and 2 (B-5233, ref. 35). The mutant B-5233/GFP was also used for neutrophil functional assays in patient 2.…”

The Sho1 Sensor Regulates Growth, Morphology, and Oxidant Adaptation in Aspergillus fumigatus but Is Not Essential for Development of Invasive Pulmonary Aspergillosis

“…The resulting strain of A. tumefaciens was designated the At sho1 strain. A sho1 mutant was constructed by A. tumefaciens-mediated transformation as described previously (27,28,29). To obtain a sho1 mutant, MA21, the At sho1 strain was cocultured with strain AF293.1 at 24°C for 48 h. Cell mixtures were grown on IMAS agar plates and then transferred to 37°C and incubated for 48 h. Transformants were scraped from plates and transferred onto glucose minimal medium agar plates supplemented with cefotaxime (200 g/ml).…”