Penicillium verrucosum

Penicillium verrucosum is a psychrophilic fungus which was discovered in Belgium and introduced by Dierckx in 1901. Six varieties of this species have been recognized based primarily on differences in colony colour: P. verrucosum var. album, P. verrucosum var. corymbiferum, P. verrucosum var. cyclopium, P. verrucosum var. ochraceum, P. verrucosum var. melanochlorum and P. verrucosum var. verrucosum. This fungus has important implications in food, specifically for grains and other cereal crops on which it grows. Its growth is carefully regulated in order to reduce food spoilage by this fungi and its toxic products. The genome of P. verrucosum has been sequenced and the gene clusters for the biosyntheses of its mycotoxins have been identified. Penicillium verrucosum was initially incorrectly placed in synonymy with the species Penicillium viridicatum by Raper and Thom. Later, after disagreements arose upon the identification and naming of these fungi, their growth rates, mycotoxin productions and sources were observed. Careful observation concluded that P. verrucosum and P. viridicatum were indeed separate species. Experimental results showed that the mycotoxins ochratoxin A and citrinin are not produced by P. viridicatum and that P. verrucosum is the only known member of the genus Penicillium to produce ochratoxin A. Penicillium verrucosum is found in temperate and cooler climates. It is found predominantly in northern Europe, including countries such as Scandinavia, Ukraine, Denmark, Sweden, United Kingdom, Yugoslavia, Italy, and Turkey, certain parts of North America, such as Canada, and parts of South America. P. verrucosum grows on grains, seeds and decaying vegetation. It is widely distributed in food (such as cereal) and animal feed where grains (usually barley, wheat and rye) are a key ingredient. Penicillium verrucosum is found to be slow-growing: it achieves between 15 mm and 25 mm of growth in diameter on both Czapek Yeast Agar (CYA) and Malt Extract Agar (MEA) after seven days. P. verrucosum has a white mycelium and greyish-green to dull green conidia on the aforementioned media. The reverse is coloured yellow brown to deep brown on CYA and dull brown to olive on MEA. Other varieties of P. verrucosum can have differently coloured conidia, including the colours dark green and blue-green. This fungus has a greater number of conidia growth on CYA than MEA. The conidia are smooth-walled and approximately 2.5 μm to 3.0 μm in diameter. These conidia begin in an ellipsoidal shape when young, and later change to a globose or subglobose shape. P. verrucosum possesses conidiophores which are usually two-stage branched (sometimes three-stage branched), giving it a brush-like appearance. The conidiophores of P. verrucosum are rough-walled with branches and metulae that are pressed closely together. The phialides of the conidiophore are short and flask-shaped with distinct necks. Penicillium verrucosum has a distinctive odour which is described as earthy and pungent. Of the genus Penicillium, only about half of the identified species are able to grow at the body temperature of mammals. P. verrucosum is not one of these species as there is usually no growth of this fungus at 37 °C. The conidia of P. verrucosum have the ability to germinate at temperatures between 0 °C and 31 °C, but optimal temperatures for germination are between 21 °C and 23 °C. Metabolic products of this fungi include 2-octen-1-ol and 1-octanol and ochratoxin A, brevianamide A, citrinin, penicillic acid, ergosterol, ergosteryl palmitate, meso-erythritol, mannitol, viridicatic acid, viridicatol, viridicatin, xanthomegnin, viomellein, rubrosulphin, viopurpurin, 3-O-methylviridicatin, cyclopenin, cyclopenol. Penicillium verrucosum produces a very potent mycotoxin called ochratoxin A (OTA). This mycotoxin is immunosuppressive and teratogenic. It has also been classified as genotoxic and a possible human carcinogen. Pigs raised in northern and central Europe develop nephritis after consumption of contaminated feed. The consumption of contaminated barley has been found to be toxic to rats and of contaminated rice has proven to be toxic to mice. Penicillium verrucosum is a contaminant of cereal crops (such as barley, maize, oats and wheat) which are used in animal feed. These grains become contaminated with this mycotoxin when they are not carefully prepared after harvest and when storage conditions are unsuitable. When grains are properly stored, OTA levels tend to average around 1 μg/kg in temperate areas.