The Aspergillus fumigatus Sialidase (Kdnase) Contributes to Cell Wall Integrity and Virulence in Amphotericin B-Treated Mice

Abstract

Aspergillus fumigatus is a filamentous fungus that can cause a life-threatening invasive pulmonary aspergillosis (IPA) in immunocompromised individuals. We previously characterized an exo-sialidase from A. fumigatus that prefers the sialic acid substrate, 2-keto-3-deoxy-D-glycero-D-galacto-nononic acid (Kdn); hence it is a Kdnase. Sialidases are known virulence factors in other pathogens; therefore, the goal of our study was to evaluate the importance of Kdnase in A. fumigatus. A kdnase knockout strain (Δkdnase) was unable to grow on medium containing Kdn and displayed reduced growth and abnormal morphology. Δkdnase was more sensitive than wild type to hyperosmotic conditions and the antifungal agent, amphotericin B. In contrast, Δkdnase had increased resistance to nikkomycin, Congo Red and Calcofluor White indicating activation of compensatory cell wall chitin deposition. Increased cell wall thickness and chitin content in Δkdnase were confirmed by electron and immunofluorescence microscopy. In a neutropenic mouse model of invasive aspergillosis, the Δkdnase strain had attenuated virulence and a significantly lower lung fungal burden but only in animals that received liposomal amphotericin B after spore exposure. Macrophage numbers were almost twofold higher in lung sections from mice that received the Δkdnase strain, possibly related to higher survival of macrophages that internalized the Δkdnase conidia. Thus, A. fumigatus Kdnase is important for fungal cell wall integrity and virulence, and because Kdnase is not present in the host, it may represent a potential target for the development of novel antifungal agents.

From simple and specific zymographic detections to the annotation of a fungus Daldinia caldariorum D263 that encodes a wide range of highly bioactive cellulolytic enzymes

“…In microorganisms, sialidases function to hydrolyze sialic acid for nutritional purposes and are involved in adhesion and host cell infection [ 33 ]. Also, an Aspergillus fumigatus sialidase (Kdnase) may be responsible for its virulence and cell wall integrity [ 34 ]. However, sialic acid is barely present in plants [ 35 , 36 ], thus sialidases may not be needed for cellulose decomposition.…”

Identifying candidate Aspergillus pathogenicity factors by annotation frequency

“…Hexokinases, specifically, are involved in morphogenesis and virulence along with their nominal roles in life-supporting sugar and Nacetylglucosamine metabolism in A. fumigatus and Candida albicans [39][40][41][42]. There are several reported disease-associated glycosylated antigens, detoxifying catalases and host-adhering sialic acids from A. fumigatus [10,[43][44][45][46][47][48][49]. A. fumigatus conidial surfaces have 3 to 20 times more sialic acids than the less virulent or nonpathogenic Aspergillus species A. auricomus, A. ornatus and A. wentii [50].…”

“…Human pathogenesis by Aspergillus species is complex and requires the normally saprotrophic Aspergillus spp. to adapt to the environment of the human lung [10]. Hospitalizations due to Aspergillus infections cost the United States an estimated 1.2 billion dollars annually [11].…”

Sialic acid and biology of life: An introduction

“…A. fumigatus has been known to express a sialidase termed as KDNase that prefers sialic acid substrate, 2-keto-3-deoxy-D-glycero-D-galactonononic acid (KDNase) and plays an important role in maintaining cell wall integrity and virulence [173]. Core 1 O-linked glycan-specific lectin, Hericium erinaceus lecin (HeL), has been isolated from the fruiting body of the mushroom Hericium erinaceus (H. erinaceus), which acts as a natural source for a sialic acid-binding lectin (SABL) [174].…”