Aspergillus clavatus

Aspergillus clavatus is a species of fungus in the genus Aspergillus with conidia dimensions 3–4.5 x 2.5–4.5 μm. It is found in soil and animal manure. The fungus was first described scientifically in 1834 by the French mycologist John Baptiste Henri Joseph Desmazières. The fungus can produce the toxin patulin, which may be associated with disease in humans and animals. This species is only occasionally pathogenic. Other sources have identified many species of Aspergillus as producing dry, hydrophobic spores that are easily inhaled by humans and animals. Due to the small size of the spores, about 70% of spores of A. fumigatus are able to penetrate into the trachea and primary bronchi and close to 1% into alveoli. Inhalation of spores of Aspergillus is a health risk. A. clavatus is allergenic, causing the occupational hypersensitivity pneumonitis known as malt-worker's lung. Aspergillus clavatus is a species of Aspergillus and is characterized by elongated club-shaped vesicles, and blue-green uniseriate conidia. The fungus was first described scientifically in 1834 by the French mycologist John Baptiste Henri Joseph Desmazières. It belongs to the Aspergillus section Clavati, (formerly known as the Aspergillus clavatus group) recognized by Charles Thom and Margaret Church (1926), alongside two species, Aspergillus clavatus and Aspergillus giganteus. In the succeeding years, four more species were discovered belonging to the Aspergillus section Clavati, which included Aspergillus rhizopodus, Aspergillus longivesica, Neocarpenteles acanthosporus and Aspergillus clavatonanicus. Later, Aspergillus pallidus was concluded to be a white variant (synonym) of A. clavatus by Samson (1979), which was supported by the identical DNA sequences of the two species. Aspergillus clavatus undergoes rapid growth, resulting in the formation of a velvety and fairly dense felt that is observed to be bluish-grey green in colour. The emerging conidial heads are large and clavate when very young, quickly splitting into conspicuous and compact divergent columns. The conidia bearing conidiophores are generally coarse, smooth walled, uncoloured, hyaline and can grow to be very long. Elongated club-shaped vesicles clavate, and bear phialides (singular: phialide) over their entire-surface, contributing to its short and densely packed structure. The sterigmata are usually found to be uniseriate, numerous and crowded. Conidia formed in them are elliptical, smooth and comparatively thick-walled. A. clavatus usually express conidiophores 1.5–3.00 mm in length, which arises from specialized and widened hyphal cells that eventually become the branching foot cells. The conidia on A. clavatus has been measured up to 3.0 – 4.5 X 2.5 – 3.5 μm. Aspergillus clavatus colonies grow rapidly on Czapek's solution agar, reaching 3.0–3.5  cm, in 10 days at 24–26 °C. Growth is usually plane or moderately furrowed, with occasional appearance of floccose strains. But generally a comparatively thin surface layer of mycelial felt is observed, which produces a copious amount of erect conidiophores. The reverse is usually uncoloured but becomes brown with passing time in some strains. While odor is not prominent in some strains, it can be extremely unpleasant in others. Large conidial heads extend from 300 to 400 μm by 150 to 200 μm when young. However with time, they split into two or more divergent and compressed cordial chains reaching 1.00 mm portraying a colour consisting of artemesia green to slate olive. The observed conidiophores grow up to 1.5–3.00 mm in length with 20–30 μm in diameter. They slowly and ultimately enlarge at the apex into a clavate vesicle, which consists of a fertile area, 200 to 250 μm in length and 40–60 μm wide. The sterigmata usually ranges from 2.5 to 3.5 μm by 2.0 to 3.0 μm at the base of the vesicle, to 7.0 or 8.0 and occasionally 10 μm to 2.5 to 3.0 μm at the apex. The conidia are comparatively thick-walled and measures 3.0 to 4.5 μm by 2.5 to 3.5 μm. While they can be larger in some strains, in others their appearance may be irregular. On malt extract agar, the structural morphology of A. clavatus appears to be different than in Czapek’s solution agar. The typical strains extracted from malt media contain less abundant conidial structures, which could be larger in size. In other (non-typical) strains, the conidial heads increase in number but decrease in size. The conidiophores range from 300 to 500 μm and bear loose, columnar heads. Typical strains may be resembled by strong and unpleasant odor whereas non-typical strains are characterized being odorless. The colonies arising from one conidium on malt extract agar, consisted of 25X10^7 conidia after being observed for six days. The phialide development and conidium formation in A. clavatus has been examined using TEM. And by using SEM, it was discovered that the first-formed conidium and phialide share a continuous wall. Additionally recombination with an albino mutant led to the production of heterokaryotic conidial heads with mixed conidial colours. A GC-content of 52.5–55% was also detected upon DNA analysis. And its soluble wall carbohydrates consist of mannitol and arabitol.