Identification and nomenclature of the genus Penicillium

Abstract

Penicillium is a diverse genus occurring worldwide and its species play important roles as decomposers of organic materials and cause destructive rots in the food industry where they produce a wide range of mycotoxins. Other species are considered enzyme factories or are common indoor air allergens. Although DNA sequences are essential for robust identification of Penicillium species, there is currently no comprehensive, verified reference database for the genus. To coincide with the move to one fungus one name in the International Code of Nomenclature for algae, fungi and plants, the generic concept of Penicillium was re-defined to accommodate species from other genera, such as Chromocleista, Eladia, Eupenicillium, Torulomyces and Thysanophora, which together comprise a large monophyletic clade. As a result of this, and the many new species described in recent years, it was necessary to update the list of accepted species in Penicillium. The genus currently contains 354 accepted species, including new combinations for Aspergillus crystallinus, A. malodoratus and A. paradoxus, which belong to Penicillium section Paradoxa. To add to the taxonomic value of the list, we also provide information on each accepted species MycoBank number, living ex-type strains and provide GenBank accession numbers to ITS, β-tubulin, calmodulin and RPB2 sequences, thereby supplying a verified set of sequences for each species of the genus. In addition to the nomenclatural list, we recommend a standard working method for species descriptions and identifications to be adopted by laboratories working on this genus.

Keywords: Aspergillaceae; Fungal identification; media; nomenclature; phylogeny.

Fig. 1

Flow diagram summarising recommended methods for the identification and characterisation of Penicillium. Frisvad & Thrane (1987, 1993), Smedsgaard (1997) and Klitgaard et al. (2014), refer to methods described for detecting extrolites in fungi. Lund (1995) introduced the Ehrlich reaction that tests for production of indole metabolites.

Fig. 2

Conidiophore branching patterns observed in Penicillium. A. Conidiophores with solitary phialides. B. Monoverticillate. C. Divaricate. D, E. Biverticillate. F. Terverticillate. G. Quaterverticillate, terms used for describing parts of conidiophores are given. Scale bar = 10 μm.

Fig. 3

Penicillium paradoxum. A. Colonies: top row left to right, obverse CYA, YES, DG18 and MEA; bottom row left to right, reverse CYA, reverse YES, reverse DG18 and CREA. B. Young sclerotia. C. Phototropic conidiophores after two weaks growth. D–H. Conidiophores. I. Conidia. Scale bars: D–I = 10 μm.

Fig. 4

Penicillium paradoxum sexual reproduction. A–C. Cleistothecia. D, E. Asci. F. Ascospores. Scale bars: A, B = 500 μm; C–F = 10 μm.

Fig. 5

Penicillium crystallinum. A. Colonies: top row left to right, obverse CYA, YES, DG18 and MEA; bottom row left to right, reverse CYA, reverse YES, reverse DG18 and CREA. B. Colony texture on MEA. C–G. Conidiophores. H. Conidia. Scale bars: C–H = 10 μm.

Fig. 6

Penicillium malodoratum. A. Colonies: top row left to right, obverse CYA, YES, DG18 and MEA; bottom row left to right, reverse CYA, reverse YES, reverse DG18 and CREA. B. Colony texture on MEA. C–G. Conidiophores. H. Conidia. Scale bars: C–H = 10 μm.