Aspergillus giganteus is a species of fungus in the genus Aspergillus (from Latin "aspergillum," meaning "holy water sprinkler") that grows as a mold. It was first described in 1901 by Wehmer, and is one of six Aspergillus species from the Clavati section of the subgenus Fumigati. Its closest taxonomic relatives are Aspergillus rhizopodus (Rai et al., 1975) and Aspergillus longivescia (Huang and Raper, 1971).
Morphology
Like the majority of Aspergillus species, A. giganteus reproduces asexually, and has not been observed in a sexual state. Similar to other species in Clavati, A. giganteus produces numerous conidiophores that are characterized by glassy and translucent stem-like structures called stipes and club-shaped aspergilla that taper towards the tips. Blue-green colored asexual spores called conidia form on these tips.
On a macroscopic level, A. giganteus colonies are characterized by their velvety texture. Colonies are often white at first, turning a pale blue-green color when exposed to light.
On a microscopic level, A. giganteus produces two types of conidiophores that have distinct stipes and vesicles. The first of these conidiophores are typically 2-3 mm tall, including stipe length. These shorter conidiophores produces clavate vesicles that are 100-250 μm long and 30-50 μm wide. The second type of conidiophores are much larger, approximately 1-5 cm long. Most of this length is due to elongated stipes. These more elongated conidiophores are phototropic, meaning that they are only able to develop and grow in the presence of light. The vesicles produced by the long conidiophores are 400-600 μm long and 120-180 μm wide, more than double the size of the vesicles produced by their shorter counterparts.
Together the vesicle and phialides form the conidial head. In A. giganteus, these heads are blue-green in color, and split into two or more columns as the mold matures. Conidia form from these conidial heads. The conidia of A. giganteus are relatively thick-walled, and are distinguishable by their smooth, elliptical appearance as well as their size (3.5-4.5 x 2.4-3.0 μm). These traits are characteristic of both types of conidiophore. A. giganteus can be distinguished form other Aspergillus species placed within the Clavati section by its microscopic morphology and by its unique combination of extrolites, which are compounds synthesized by and then excreted by cells in defense against bacteria and other fungi. Morphologically, A. giganteus lacks the rhizoidal foot cells present in A. rhizopodus, and has clavate vesicles that stand in contrast to the elongated vesicles of A. longivesica. In terms of extrolite synthesis, although A. giganteus produces mycotoxins and antibiotics that are characteristic of all Clavati section species (such as patulin, tryptoquivalines and tryptoquivalones, and alpha-sarcins), it also produces extrolites not synthesized by its closest relatives. These include several different carotinoids and penicillin-like clavinformin.
Ecology
A. giganteus is found worldwide, and has been officially documented in Nigeria, the United States, Egypt, Mexico, Panama, Germany, Suriname, the Netherlands, and Poland. It is most often dung-borne, but will grow in alkaline soil and wood substrates. As a saprotrophic mold, A. giganteus gets its energy by absorbing nutrients from the substrates it grows in. Although many other Aspergillus and Clavati section species are known pathogens of humans, A. giganteus does not have any reported pathogenic effects.
In the lab, A. giganteus has been cultivated on both Czapek yeast extract agar (CYA) plates and Malt Extract Agar Oxoid® (MEAOX) plates, as shown below.
Economic relevance
Antifungal protein (AFP) A. giganteus produces an antifungal protein (AFP) that has potential applications for preventing fungal infection in both pharmaceutical and agricultural settings. AFP has been shown to restrict the growth of numerous economically-important filamentous fungi. These include Aspergillus fumigatus, the main cause of aspergillosis in humans, and other Aspergillus species; Fusarium oxysporum and related Fusarium species, common pathogens of tomato, bean, banana, melon, cotton, and chickpea plants; Magnaporthe grisea, a pathogen of rice and cereal crops; and Botrytis cineara, pathogenic to geranium and other economically important ornamental plants. Additionally, AFP may restrict the growth of the oomycete Phytopthera infestans, the pathogen infamous for causing late blight in potatoes (the main cause of the Great Famine of Ireland) and tomatoes.