Polyphasic taxonomy of Penicillium subgenus Penicillium A ... - CBS

J.C. FRISVAD &R.A.SAMSONcies is not presented, but will be published in additionalpapers in this volume and elsewhere as thesetwo aspects, cladification and classification, are absolutelynecessary in future monographs.HistorySeveral species of subgenus Penicillium were describedby Dierckx (1901), Thom (1906, 1910), Westling(1911), Biourge (1923) and Zalesky (1927).Despite treatments of some of those species by Thom(1930) and Niethammer (1949), the first effectivesynthesis of the species was written by Raper andThom (1949). They placed these species in theirsubsections Asymmetrica-Lanosa, -Funiculosa, -Velutina and -Fasciculata, with one species, P. olsonii,being placed in Biverticillata-Symmetrica. Abe(1956) mostly followed Raper and Thom (1949) anddescribed some new varieties. Fassatiova (1977) alsotreated many of the fasciculate species in her emendeddescription of the series Expansa. Samson et al.treated most of the terverticillate species in threestudies (1976, 1977a & b) and Ramirez (1982) followedtheir mainly micromorphologically basedtaxonomy. Pitt (1973; 1979) reintroduced somephysiological characters, such as growth rates atdifferent temperatures and water activities and gatheredthe terverticillate Penicillia with flask shapedphialides in subgenus Penicillium. He placed P. gladiolias a synonym of Eupenicillium crustaceum and P.sclerotigenum in subgenus Furcatum, and included P.fennelliae and P. lanosum in subgenus Penicillium.This overall concept of subgenus Penicillium is verysimilar to the present day placement of species in thesubgenus (as presented by Frisvad et al., 2000) orsequence based ribosomal DNA phylogeny (Peterson,2000). The series classification of Pitt and Cruickshank(1990) based on colony diameters and micromorphologyis, however, very different from that ofFrisvad et al. (2000).Secondary metabolites (extrolites), often recognisableas diffusible colours, colony reverse colours andexudate colours, have played a special role in fungaltaxonomy. Usually colours, especially conidiumcolour, are regarded as part of morphology. Thesecolours can be subdivided into melanin and proteinmelanin complexes that give fungal conidia theirphysical strength, hardiness and radiation protectionand other colours (and volatiles) that often acts asecological signals (Wicklow, 1986). Raper and Thom(1949) mentioned citrinin as a common extrolite inseveral P. citrinum strains, but did not ascribe anytaxonomic value to it. Ciegler et al. (1973) usedextrolites in their subdivision of one species, P. viridicatum,but concluded that” production of similarmetabolic products does not provide an adequate basisfor recognition of a new taxon“, based on the adviceof K.B. Raper. Frisvad (1981) was the first to suggestthat extrolites could be used directly in Penicilliumtaxonomy and this was followed up by two studies onmany of the species in subgenus Penicillium (Frisvadand Filtenborg, 1983; 1989, 1990a), where it wasshown that extrolites are of particularly high value in ataxonomic sense (Frisvad et al., 1998). Later a seriesof studies with increasingly advanced instrumentationhas confirmed the value of both non-volatile andvolatile extrolites in taxonomy (Lund and Frisvad,1994; Svendsen and Frisvad, 1994; Larsen and Frisvad,1995 a & b; Smedsgaard and Frisvad, 1996).Extracellular enzyme production was suggested foruse in Penicillium taxonomy by Frisvad (1981).Profiles of isozymes were introduced by Cruickshankand Pitt (1987a & b) for subgenus Penicillium, butwere later shown to be difficult to reproduce (Patersonet al., 1989). In some cases, isozyme profiles supportedsynonymies accepted by Samson et al. (1976)and Frisvad and Filtenborg (1983), e.g. the synonymyof P. resticulosum with P. expansum (Cruickshankand Pitt, 1987a), but rejected by Pitt (1979), in othercases for example the claimed synonomy of P. aurantiovirenswith P. expansum (Pitt & Cruickshank,1990) proved to be incorrect. In general the isozymeprofiles appear to support the species series suggestedin this paper. Isozyme profiles showed that P. brevicompactumand P. olsonii were closely related (Cruickshank& Pitt, 1987) in agreement with ouremended series Olsonii, still Pitt and Cruickshank(1990) placed P. brevicompactum in series Urticicolaand P. olsonii in series Olsonii. Using a more detailedprotocol than that of Cruickshank (1983) and Cruickshankand Wade (1980), Banke et al. (1997) were ableto classify isolates into species in the series Chrysogena.It seems that detailed analyses are needed toachieve resolution at the species level (Rosendahl andBanke, 1998). The latter authors also emphasize thatvariation within a species and statistics need to beconsidered. Filtenborg et al. (1996) suggested thatextracellular enzymes may play an important role inthe specific association of fungal species with theirhabitat, so these methods appear to be promising forfuture polyphasic taxonomic investigations.Bridge at al. (1989 a & b) attempted to classify theterverticillate Penicillia by using a phenotypic approach.Their results were difficult to evaluate, becausemany isolates clustered tightly, even thoughthey were actually very different. For example isolatesof P. expansum and P. aethiopicum clustered eventhough they have no extrolites in common, whiledistinct taxa such as P. coprophilum had isolatesplaced in several different clusters (Frisvad andFiltenborg, 1989).2