Understanding the Role of Septins in Aspergillus fumigatus Growth and Development

Ref ID: 19606

Author:

JM Vargas-Muniz1*, PR Juvvadi2, F Lamoth2, WJ Steinbach1,2

Author address:

1Molecular Genetics and Microbiology, Duke University Medical Center, Durham, USA
2Pediatrics, Duke University Medical Center, Durham, USA

Full conference title:

6th Advances Against Aspergillosis 2014

Abstract:

Purpose:
A. fumigatus hyphal growth is required for invasive disease, and both the cell wall and septa provide
critical structural support for proper hyphal extension. Septins are conserved GTPases involved in
several cellular processes, such as cell wall integrity, cytokinesis, and septation. The A. fumigatus
genome contains five genes encoding for septins: AspA, AspB, AspC, AspD, and AspE. AspE is
specific to filamentous fungi. Although the localization of septins has been studied in A. fumigatus,
how each of these septins contributes to hyphal growth and virulence has never been examined.
Therefore, an understanding of their precise functions in hyphal morphogenesis will not only lead to
fundamental knowledge but also to potential identification of novel antifungal targets.
Methods:
We generated six septin deletion strains (916;aspE, 916;aspD, 916;aspB, 916;aspE916;aspD, 916;aspE916;aspB and
916;aspE916;aspD916;aspB) in the A. fumigatus akuKU80 background to examine the role of these septins
in A. fumigatus growth and pathogenesis. Radial growth was assessed on solid media, conidiation
quantified, and inter-septal distances measured by staining with 0.1% aniline blue. To determine the
role of septins in cell wall integrity, each septin deletion strain was treated with cell wall inhibitors
caspofungin, a β -glucan synthase specific inhibitor, and nikkomycin Z, a chitin synthesis inhibitor.
Results:
Single, double, or triple deletion of the septin genes did not result in any significant radial growth
defect under normal growth conditions. However, the 916;aspD, 916;aspB, 916;aspE916;aspD, 916;aspE916;aspB
and 916;aspE916;aspD916;aspB strains have a significant reduction in conidiation comparted to wild-type
strain. In contrast to the inter-septal distances of the apical and subapical compartments of the wildtype
strain (76.30 μm, 23.15 μm), the 916;aspE (170.61μm [P<0.001], 44.13μm [P<0.001]), 916;aspB (177.96μm [P<0.001], 60.09μm [P<0.001]), 916;aspD (96.55μm [P=0.0025], 31.60μm [P<0.001]), 916;aspE916;aspD (162.62μm [P<0.001], 46.06μm [P<0.001]), and 916;aspE916;aspD916;aspB (255.63μm [P<0.001], 92.44μm [P<0.001]) strains exhibited an increase in inter-septal distances of both compartments. Interestingly, the apical compartment of the 916;aspE916;aspB double deletion strain was also significantly larger than the apical compartment of 916;aspE and 916;aspB strains [P=0.002]. The 916;aspB, 916;aspE916;aspB and 916;aspE916;aspD916;aspB strains were also more susceptible to nikkomycin Z and caspofungin. Additionally, the caspofungin paradoxical effect (increase in growth following exposure to higher concentrations of caspofungin) was slightly abrogated following aspB deletion. Conclusion: We demonstrated that septin genes are dispensable for basal growth of the fungus, but important for maintenance of inter-septal distances through regular septation, conidiation, and for cell wall integrity. Specifically, deletion of aspB resulted in increased susceptibility to nikkomycin Z and caspofungin. This is the first exploration of septins in a human pathogenic filamentous fungus, and understanding this unique aspect of A. fumigatus biology will provide critical insight into disease pathogenesis that could lead to identification of novel drugs targets to ultimately improve clinical outcome.

Abstract Number: 131

Conference Year: 2014

Link to conference website: http://www.AAA2014.org

New link: NULL

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