Penicillium is a genus consisting of a group of fungi having around 354 accepted species. It also refers as “Doctor Fungi” as few members of the genus (Penicillium) can produce antibiotic to inhibit the growth of certain bacteria. Penicillium species are ubiquitous, where many produce potential mycotoxins, few produce medically useful antibiotics, and some are important in the process of cheese making. Due to non-distinct sexual phase, Penicillium species also refers to as “Deuteromycetes or Fungi imperfecti”. Among the group of Penicillium species, excluding P.marneffei, all are filamentous in structure.
Characteristics of Penicillium
Penicillium belongs to the Ascomycetes group of fungi and also refers to as “Ascomycetous fungi”. It also produces characteristic bluish-green spores, due to which it also refers to as “Blue-green mould”.
Habitat and Distribution:
It is commonly present in the soil, dead organic matter of plant and animal waste, air etc. These are having a heterotrophic or saprophytic mode of nutrition. Penicillium species are generally ubiquitous and widespread in distribution.
The growth of Penicillium species occurs at a mesophilic range of temperature (Between 20 – 30 Degrees Celsius), and a pH of 3 – 4.5. Maximum growth achieves at a temperature of 23 degrees Celsius. The water activity must be in a range of 0.78 – 0.88.
Some strains of genus Penicillium produce various medically useful antibiotics. The first antibiotic was isolated from Penicillium notatum, by a scientist named Alexander Flemings in the year 1929, which he named as “Penicillin”. Penicillin functions as an antibacterial agent that mainly resists the growth of gram-positive bacteria.
Later another antibiotic was introduced as “Griseofulvin” from Penicillium griseofulvum and used as an antifungal agent to inhibit the activity of dimorphic fungi.
It can be cultured on Czapek Dox agar and 2% Malt extract agar at a temperature between 23-25 degrees Celsius. Almost all the strains require a sporulation period of a maximum of 7 days. The identification of the specimen involves the mounting it in a lactophenol cotton blue stain over a glass slide.
Structure of Penicillium
All the species (except P. marneffi) show the following similar features:
Colony: Fast-growing and flat in appearance.
Colony texture: Appears velvety or cottony.
Colour of the colony: Initially appears white and later turns blue-green, olive-grey.
P. marneffi produces flat, radially sulcate colonies. The colour of the colony towards the centre appears bluish-green and white at the periphery, after incubation at a temperature of 25 degrees Celsius. Oppositely, at a temperature of 37 degrees Celsius, it produces convoluting colony having cream to slightly pink colour.
The vegetative structure of Penicillium comprises of the following elements.
It’s a vegetative part having a profuse branching, septate, cylindrical and thin-walled hyphae. The cell wall comprises of glucan. Hyphae appear small, septate, hyaline and 1.5-5 µm in diameter. A septum consists of a central pore. The growth of mycelium can occur superficially on the substratum or deep inside the substrate. A single cell of mycelium may contain one to many nuclei, i.e. Uni-nucleate or multi-nucleate.
Penicillium species are generally consisting of a long, filamentous-like conidiophore. Depending on various species, the conidiophore may be either symmetrical or asymmetrical in structure and can be simple or branched. Metullae is a secondary branch originates from the long conidiophore, and also refers as primary sterigmata. Phialides is the secondary sterigmata that resemble the flask-like structure pinches out of the secondary branch (metullae) of the conidiophore. The arrangement of phialides is very typical which resemble the brush-like clusters known as “Penicilli”.
The members of genus Penicillium generally comprise of conidial chains on the flask-like phialides. These are having a diameter of 2.5-5 µm. The conidial spores or conidiospores exist as round and unicellular cells. It has an arrangement in bicipital succession.
Some of the interesting facts are given below:
Penicillium is a term derived from a Latin word “Penicillus” which means paintbrush as its structure is very much similar like a paintbrush. Penicillin was the first antibiotic introduced by a scientist named Alexander Fleming, which he isolated from the species (Penicillium notatum).
The growth of Penicillium species is the common cause of fruits and vegetable decay and one of the primary reason of post-harvest losses. It can also affect the economy, as it may even grow on fabrics, leather, wood etc.
It can grow on a variety of foodstuffs (commonly fruits and vegetables) and results to cause of food spoilage. Some of the Penicillium strains produce mycotoxins that may cause various allergic reactions.
Example: P. verrucosum releases ochratoxin-A mycotoxin that shows nephrotoxic (kidney damage) and carcinogenic effects (cancer).
Some of the strains are harmful to the humankind and the economy of our country. Still, few are also crucial in the field of industrial field, medicine, food microbiology, bio-deterioration etc. Penicillium strains play an essential role in the commercial production of cheese, organic acids and antibiotics.
One of the easiest ways to identify Penicillium species is through the branching pattern of the conidiophore. The conidiophores give rise to the secondary branches (Metullae) that further give rise to the tertiary branches (Phialides or Sterigmata), which makes it distinct from the other groups of fungi.