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. 2009 Oct 30;4(10):e7673.
doi: 10.1371/journal.pone.0007673.

Aspergillus terreus accessory conidia are unique in surface architecture, cell wall composition and germination kinetics

Eszter Deak  1 , Selwyn D Wilson, Elizabeth White, Janice H Carr, S Arunmozhi Balajee
Affiliations

Aspergillus terreus accessory conidia are unique in surface architecture, cell wall composition and germination kinetics

Eszter Deak et al. PLoS One. .

Abstract

Infection with Aspergillus terreus is more likely to result in invasive, disseminated disease when compared to other Aspergillus species; importantly this species appears to be less susceptible to the antifungal drug amphotericin B. Unique to this species is the ability to produce specialized structures denoted as accessory conidia (AC) directly on hyphae both in vitro and in vivo. With the hypothesis that production of AC by A. terreus may enhance virulence of this organism, we analyzed the phenotype, structure and metabolic potential of these conidia. Comparison of A. terreus phialidic conidia (conidia that arise from conidiophores, PC) and AC architecture by electron microscopy revealed distinct morphological differences between the two conidial forms; AC have a smoother, thicker outer cell surface with no apparent pigment-like layer. Further, AC germinated rapidly, had enhanced adherence to microspheres, and were metabolically more active compared to PC. Additionally, AC contained less cell membrane ergosterol, which correlated with decreased susceptibility to AMB as determined using a flow cytometry based analysis. Furthermore, AC exhibited surface patches of beta1-3 glucan, suggestive of attachment scarring. Collectively, the findings of this study suggest a possible role for AC in A. terreus pathogenesis.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Aspergillus terreus Accessory conidia production.
Light microscopic images of accessory conidia recovered from A. terreus isolates IBT 12713 (A), P12 (B), E5 (C) demonstrating globose (A) and club-shaped (B) and in pair (C) phenotypes. Scale bars represent 20 µm.
Figure 2
Figure 2. Cell wall architecture of phialidic and accessory conidia of A. terreus.
Comparative scanning electron microscopy (A and B) and transmission electron microscopy (C and D) of A. terreus phialidic conidia (A and C) and accessory conidia (B and D). Conidia were harvested and fixed in 5% glutaraldehyde for microscopy. Dashed arrow indicates melanin like layer and solid arrow indicates the cell wall (C and D); 10–15 conidia were imaged, p = 0.0003.
Figure 3
Figure 3. Metabolic activity of phialidic conidia and accessory conidia using the XTT assay.
XTT absorbance (OD490) of phialidic (dashed line) and accessory conidia (solid line) was measured at 0, 0.5, 1, 2, 3, 4, 5, 6, and 7 hours after subtraction of background OD (OD of wells with XTT alone). Error bars represent standard error of experiments performed in triplicate.
Figure 4
Figure 4. β1-3-glucan expression on phialidic conidia and accessory conidia.
Staining for β1-3-glucan surface exposure on A. fumigatus conidia (A), A. terreus phialidic conidia (B) and A. terreus accessory conidia (C) was performed and evaluated by fluorescence microscopy. Arrows denote the β1-3-glucan staining on accessory conidia.
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