Aspergillus is a common fungus, which is present everywhere, in the soil, air, water etc. or we can say it is present in a wide range of conditions. Therefore, these are ubiquitous in nature. It consists of several 100-500 species among which some are economically important and some are deleterious i.e. pathogenic. It was named in 1729, by the Antonio Micheli who was the director of the public gardens in Florence.
- Kingdom: Fungi
- Division: Ascomycota
- Class: Eurotiomycetes
- Order: Eurotiales
- Family: Trichocomaceae
- Genus: Aspergillus
Structure of Aspergillus
Aspergillus has a filamentous structure. It consists of the following components in its cell structure that include:
Foot cell: It is the vegetative structure of the cell which also refers to the vegetative hyphae. It is found attached to the substratum through which this hypha absorbs the nutrient for further growth. Foot cell is generally L or T shaped. When it grows, it gives rise to the conidiophore.
Conidiophore: It is long, slender and perpendicular to the foot cell or vegetative hyphae. Conidiophore is the erect hyphal branch which enlarges at an apex and gives rise to the vesicle.
Vesicle: It is rounded, elliptical or club-shaped which develops a layer of cells refers to phialides.
Conidia: These are the exogenous reproductive structure that arises from the sterigmata. Conidia forms in chains and is having a basipetal arrangement where the youngest conidia present at its base and the oldest conidia present at the top.
Mycelium: It is hyaline, septate, branched, multicellular, multinucleated and tubular in structure. Mycelium surrounds by the two layers namely inner layer (made of cellulose) and an outer layer (made of chitin).
Cytoplasm: It is granular in appearance and consists of cytoplasmic bodies such as mitochondria, endoplasmic reticulum, ribosomes, vacuoles etc.
- Aspergillus also refers to black or green mould because the majority of them form black and green spores that grow on the substratum gives a mouldy appearance.
- It also refers as sac fungi because of the fact that the sexual spores produce within the sacs (Asci) known as ascospores.
- The mode of nutrition is “Heterotrophic“, which depend upon others for the food and nutrition.
- Aspergillus are common mould which is widespread and ubiquitous in nature.
- It is able to tolerate extreme environmental conditions like high temperature.
- Most of the Aspergillus species reproduce asexually by the means of conidiospores and few grow sexually by the means of ascospores.
- Aspergillus species are Terricolous i.e. most of the species grows on the ground or soil.
- The spores of Aspergillus are abundant in nature and can be saprophytic and parasitic.
- Chlorophyll is absent in this i.e. these can not prepare their own food.
- Aspergillus obtains nutrition from the environment by the means of vegetative hyphae, which then grows to produce reproductive structure i.e. spores.
- The hyphae of the Aspergillus is of two types:
- Vegetative hyphae: It helps in Nutrient absorption.
- Reproductive hyphae: It helps in the Production of fungal spores.
Reproduction of Aspergillus
The Aspergillus reproduces by the three methods:
Vegetative reproduction occurs by the fragmentation method, in which a vegetative hypha breaks into few fragments which then develops into a new vegetative body.
The asexual reproduction of Aspergillus includes the following steps:
- First, the foot cell develops a small outgrowth by absorbing nutrient from the substratum.
- Then, the foot cell gives rise to the long and slender hyphae refers to conidiophore.
- After that, the conidiophore grows and enlarges at the apex by the nuclear division to form a vesicle.
- The vesicle then grows and undergoes mitotic nuclear divisions to form sterigmata.
- Sterigmata are uninucleate which also undergoes mitotic division and transfers one nucleus to the secondary sterigmata.
- These secondary sterigmata then form a chain of conidia in a basipetal arrangement.
- After that, conidiospores gets detached from the hyphae either accidentally or through certain environmental factors and remains in the soil in the dormant state.
- When the spores get favourable conditions they form a germ tube and undergo germination to form new vegetative hyphae.
The sexual reproduction occurs rarely only in the heterothallic species which contains both male and female hyphae. A.heterothallic is an example of the species that undergo sexual reproduction.
The heterothallic hyphae consist of female hyphae that refer to Ascogonium and the male hyphae which refer to Anthredium.
Ascogonium divides into three parts (Basal, middle and apical), which are multinucleate, septate and loosely coiled. Anthredium divides into two parts (Upper and lower) which are unicellular, multinucleate and septate.
The sexual reproduction of Aspergillus involves the following steps:
- First, the female and the male hyphae contacts with each other.
- After that fusion occurs between the female and male hyphae where the transfer of the Anthredium contents transfer to the Ascogonium through the point of junction. Plasmogamy occurs in the ascogonium where cytoplasmic division takes place.
- After Plasmogamy, the ascogonium develops into the fruiting body refers to Ascocarp where the karyogamy occurs. After karyogamy occurs by which 8 ascospores forms inside the Asci (Saclike structure) which is generally pear-shaped.
- Then maturation of ascocarp occurs which forms a protective covering refers to peridium.
- Then by the maturation of the asci, the ascospores release out by the lysis of asci and then by ascocarp wall.
- The ascospore remains dormant in the environment and is unicellular, wheel-shaped and 5µm in diameter. Its wall of ascospore differentiates into three layers: An outer layer is thick, the middle layer refers to as epispore and the inner layer is thin.
- And, on favourable conditions, they germinate new vegetative hyphae by the formation of a germ tube.
- A.nidulans is extensively used as model organisms for the study of the parasexual cycle, regulation of metabolic pathway, cell cycle, hyphal polarity etc. in the filamentous fungi.
- Uses in the bioassay of soil for tracing out of the elements like copper and arsenic by A.niger and A.virens respectively.
- Aspergillus species are capable of low-rank coal solubilization.
- Uses in the production of organic acid like gluconic acid, citric acid etc. by A.niger, A.fumaricvus respectively.
- It releases enzymes which play an important role in the decomposition of organic matter.
- Uses in the production of antibiotics like Proliferin, Fumigalin, Aspergillin etc by A.proliferans, A. fumigatus and A.niger respectively.
- Aspergillus helps in nutrient recycling, where they breakdown the complex polymeric compounds into simpler ones by secreting some enzymes and metabolites which further absorbs by the hyphae.
- A.oryzae uses in the production of sake wine by fermenting rice.
- Uses in the production of amylase by A.niger and A.oryzae.
- Some species of Aspergillus are pathogenic, for example, A.fumigatus which is opportunistic fungus cause a fatal disease “Aspergillosis” in humans.
- In animals, particularly chickens species cause brooder disease which is generally pneumonia of lungs.
- It produces secondary metabolites that are harmful to human life.
- Some of the strains like A. flavus, A. paraciticus, A.niger etc. produce carcinogenic mycotoxins like aflatoxin and ochratoxin.
- Several species of Aspergillus contaminate the food products including fruits, vegetables, grains etc. by the production of their toxic metabolites.
- In plants, it causes fruit rot in many fruits like mango, date, pomegranate etc.
- Aspergillus also refers to “weed or contaminant of the laboratory“, which is able to contaminate the biological culture like bacterial and fungal culture.
Therefore, there are both advantages and disadvantages of the Aspergillus which can cause a huge ecological impact by imposing positive and negative effects.