Copper deficiency in potato dextrose agar causes reduced pigmentation in cultures of various fungi

Abstract

Potato dextrose agar (PDA) is one of the most commonly used media for the isolation and cultivation of fungi, with morphological features and pigmentation in culture often being important for identification of cultures. Cultivation of various fungi on different brands and batches of powdered (commercial) potato dextrose media revealed deficient pigmentation in five of 10 media tested. Reduced pigmentation on these media was correlated with low levels of copper and colony colour was restored by the addition of copper. Deficient pigmentation was most pronounced when copper levels in the medium were below 50 ng mL(-1) (50 p.p.b.; 0.8 microM). Differences in pigmentation and laccase activity of spore and mycelial preparations were quantified for representative species belonging to the genera Aspergillus, Fusarium, Trichoderma, Cladosporium and Penicillium grown on PDA containing different amounts of copper. A strong positive correlation between laccase activity and copper levels was observed. Differences were also found between batches of raw potatoes, with organically cultivated tubers having higher copper levels than those grown by conventional methods, possibly because of the use of copper-based fungicides in the former case. Routine addition of 1000 ng mL(-1) copper (or standard trace element solutions) to PDA and other undefined media is advised to avoid atypical culture pigmentation and possibly other consequences of reduced activity of copper-requiring enzymes.

Synthesis and assembly of fungal melanin

“…In Gaeumannomyces graminis , addition of copper to the medium results in dark cultures and the cells have a layer of melanin in the cell wall visible by TEM (Caesar-Tonthat et al 1995). Similarly, variation in copper levels among commercial fungal media (potato dextrose agar) correspond to variable pigmentation in multiple fungal species including Trichoderma harzianum , Stachybotrys atra , Fusarium culmorum , and Cladosporium herbarum (Griffith et al 2007). Molecular studies also highlight the importance of copper in melanization.…”

Laccases Involved in 1,8-Dihydroxynaphthalene Melanin Biosynthesis in Aspergillus fumigatus Are Regulated by Developmental Factors and Copper Homeostasis

“…The importance of copper in melanization has been highlighted in a few studies; this importance is likely due to the requirement of copper as a cofactor for laccases (30,31). In A. nidulans, a mutation in the ygA gene that encodes a transporter produces yellow conidia at high pH and green conidia at low pH (32,33).…”

Accumulation of copper in Trichoderma reesei transformants, constructed with the modified Agrobacterium tumefaciens-mediated transformation technique

“…In general, wild-type strains grow faster than AT01 under the same concentration of copper. Griffith et al (2007) also found that adding copper to potato/dextrose/agar exerts a significant impact on the growth of fungi. Furthermore, the incubation time increases along with the growth of wild-type strains when the copper exceed 2.1 mM.…”