Antonie van Leeuwenhoek 43 (1977) 341-350 341 The taxonomy of Penicillium species from fermented cheeses R. A. SAMSON 1 , CHRISTIANE ECKARDT 1'3 AND R. O R T H 2'4 1Centraalbureau voor Schimmelcultures, Baarn, The Netherlands, and 2Bunde~forschungsanstalt fiir Erndhrung, D-7500 Karlsruhe, Germany SAMSON,R. A., ECKARDT,C. and ORTH,R. 1977. The taxonomy of Penicillium species from fermented cheeses. Antonie van Leeuwenhoek 43: 341-350. The taxonomy of the Penicillium camernberti and P. roqueforti series is re-investigated. P. caseicolum Bainier is regarded as a synonym ofP. camemberti Thorn on the basis of morphological characters. P. casei Staub is considered to be identical with P. verrucosum Dierckx var. cyclopium (Westting) Samson, Stolk et Hadlok. Descriptions and illustrations of P. camernberti and P. roqueforti Thorn are given. The occurrence and mycotoxin production of both species are shortly discussed. INTRODUCTION Members of the genus Penicillium are commonly found in food products. Several species are known to cause spoilage (e.g.P. digitatum Sacc. and P. expansum Link ex S. F. Gray) or to produce toxic substances ( e . g . P . griseofulvum Dierckx and P. rubrum Stoll). Some other species like P. roqueforti and P.camemberti have long been used in the production of such cheeses as Roquefort, Gorgonzola, Camembert and Brie. As early as the turn of the century Johan-Olsen ( = Sopp) (1898), Dierckx (1901) and Thorn (1906) and others reported on these fungi, especially dealing with their occurrence on cheese and the role in the fermentation process. In current food microbiology the Penicillium species which are used as fungal starters for the production of different types of cheese have become of special interest because of their possible toxic metabolites (Gibel, Wegner and Wildner, 1971 ; Frank, 1973 ; Anon., 1974). In their Manual of the Penicillia, Raper and Thom (1949) paid special attention to the cheese-borne species and placed them in two separate series, the P. roqueforti and the P. camemberti series. The identification of the members 3 Present address: Bundesanstalt fiir Fleischforschung, D-8650 Kulmbach, Germany. 4 Present address: Henkel & Cie GmbH, Dept. of Microbiology, D-4000 Dtisseldorf, Germany. 342 R. A. SAMSON, C. ECKARDT AND R. ORTH o f these two series sometimes proved to be difficult because the species show morphological similarities to other very c o m m o n Penicillia such as P. verrucosum var. cyclopium (Samson, Stolk and Hadlok, 1976). F u r t h e r m o r e in the literature and also by cheese manufactures, some old and doubtful names like P. glaucum Link and P. candidum Link are still infrequently used. This paper deals with a re-investigation o f the species belonging to the P. roqueforti and P. camemberti series. The conidiophore terminology used in this paper is that o f Samson et al. (1976), Penicillium camemberti Thorn. - - Bull. Bur. Anim. Ind. U.S, Dept. Agric. 82: 33. 1906. - Penicillium aromaticum III Johan-Olsen. Zentbl. Bakt. ParasitKde, Abt. II. 4 : 161.1898. Penicillium album Epstein, - - Arch. Hyg. Ig: 360. 1902 (non P. album Preuss. - - Linnaea 24: 135. 1851 or P. album Riv. - - Paras. V6get. p. 452. 1873) = P. epsteinii Lindau apud Rabenhorst, Deutschl. Krypt. Flora, Pilze, Bd. 8, t66. 1907. - PeniciItium rogeri Wehmer. apud Lafar. - - Tech. Mycol. 2 : 226. 1906. PenicilIium caseicotum Bain.-- Bull. Soc. Mycol. Fr. 23: 94. 1907. -Penicittium camemberti Thorn var. rogeri Thorn. - - Bull. Bur. Anita. Ind. U.S. Dep. Agric. 118: 52. 1910. Colonies on Czapek agar growing slowly, attaining a diameter o f 2-3.5 c m within two weeks at 25 C, consisting o f a raised fioccose aerial mycelium usually up to 1 cm high, at first white, remaining so or changing to yellowish, pinkish Fig. 1. Penicilfium camemberti, conidiophores and conidia. PENICILLIUMSPECIESFROM FERMENTEDCHEESES 343 (rare) or grey-greenish, the latter shade usually appearing rather late in the colony development. Odour mouldy or not pronounced. Exudate rarely present as colourless drops. Conidiogenous structures arising from submerged hyphae, occasionally from aerial hyphae. Conidiophores up to 500 #m long, 2.5-4.0 /~m wide, two- to three-stage branched; conidiophore stipe roughwalled, rarely smooth-walled, ornamentation sometimes appearing later in the development. Metulae 8-14 × 2.5-3.0 #m, giving rise to 3 to 6 phialides. Philialides flask-shaped with short necks, 10-13 × 2.2-2.5 /~m. Conidia in tangled chains, globose to subglobose, or broadly ellipsoidat, hyaline or slightly greenish, 4.0-5.0 × 3.0-4.5 # m (Fig. 1). Colonies on malt agar similar, but mostly with more conidiophores which are more roughened, than on Czapek agar. Material examined : CBS 299.48 = NRRL 877 = ATCC 4845 = IMI 27831, type culture of P. camemberti, isolated from camembert cheese by C. Thorn, Storrs, Connecticut, USA. CBS 123.08, type culture of P. camemberti var. rogeri, isolated from camembert cheese by C. Thorn. CBS 303.48 = NRRL 875 = ATCC t0433 = IMI 28810, type culture of P. caseicotum, originating from the collection of G. Bainier, Paris. CBS 249.77 A and B, starter culture "P. candidum', used for the production of Camembert in Germany. CBS 248.77 received as P. camemberti var. candidum III C3, used by Gibel et al. (1971) in their feeding experiments with rats. Numerous other strains isolated from German and French Camembert and Brie cheeses and smoked pork. This material also includes the isolates described by Frank (1966). Discussion The species of P. camemberti and P. caseicolum were considered by Raper and Thorn (1949) as two distinct taxa. They were separated on the basis of the colony difference: pale green in P. camemberti and white in P. caseicolum. According to Raper and Thorn (1949) both species differ also in physiological and biochemical characters as revealed in cheese manufacture. In an earlier paper Thorn (1910) considered the white form to be a variety of P. camemberti and called it P. camemberti var. rogeri. In 1930, however, Thorn placed this white variety in synonymy with P. caseicolum. The status of P. camemberti and P. caseicolum has been discussed in an extensive study by Leonidse (1930). In that study it was shown that both species do not differ significantly in their morphological or physiological characters. Leonidse (t930) also demonstrated that the grey-green colony colour of P.camemberti is unstable. Cultivation of green strains on a sucrose-containing medium (after Bezssonof, 1918) revealed only yellow or uncoloured. A similar comparative study on the morphology and physiology of P. camemberti and P. caseicolum by F r a n k (1966) also showed that both species are very similar. The present study of the type strains and several additional strains of both 344 R. A. SAMSON, C. ECKARDTAND R, ORTH species demonstrates that a species delimitation based on colony colour difference is unreliable. Cultures of P. camemberti remain white on media with higher sucrose concentrations or change to pale yellow. Some strains of P. caseico!um become yellow or even pinkish on normal Czapek agar. The conidiophore morphology of P. eamemberti and P. caseicolum is very similar. The branching pattern of both species is identical, though the roughness of the wall may vary. In most isolates the conidiophore stipes may become roughened in old cultures. Phialides and conidia are identical in both taxa. In spite of the small colour difference between P. eamemberti and P. caseicolum, these taxa cannot be separated and are synonymized under the older name P. camemberti Thorn. In the literature P. candidum Link and P. album Preuss have often been cited as used in cheese manufacturing. No type material exists of either species and their descriptions are very inadequate. The two species can therefore best be considered doubtful taxa. The taxonomic status of P. aromaticum III JohanOlsen has been discussed by Thorn (1910, 1930) and Raper and Thorn (1949) and we accept their suggestion that this species may be identical with P. camemberti although no type material exists. P. camemberti resembles P. verrucosum Dierckx vat. album (G. Smith) Samson, Stolk et Hadlok (1976) in its rough-walled conidiophores. The latter species has, however, fasciculate colonies with an earthy odour and uniform globose to subglobose conidia. In many studies the enzyme activities of P. camemberti and P. caseicolum have been investigated (Raper and Thorn, 1949; Jacquet et al., 1957; Prok~ and Cingro~ov/~, 1962; Eichler, 1968; Dole~lek and Minarik, 1968; Kikuchi and Takafuji, 1971 ; Lenoir et al., 1971; Lamberet and Lenoir, 1972). At present, camembert cheeses are mostly fermented by the white forms of P. camemberti ( = P. caseicolum) because the white mycelium gives the cheese more aesthetic appearance (Lfibenau-Nestle and Mair-Waldburg, 1968). During our studies we also obtained a few isolates with green conidia from cheese. Most isolates, however, were white, yellowish or pinkish. Penicillium casei Staub. - - Zentbl. Bakt. ParasitKde, Abt. II. 31 : 454. 1911. This species has been re-described by Thorn (1930) and Raper and Thorn (1949), based on a culture (CBS 302.48 = NRRL 844) isolated from Swiss cheese. This culture does not represent the type strain described by Staub (1911). Examination of Thorn's strain and the original description of P. casei proved that this species can best be considered to be a synonym of P. verrucosum var. cyclopium (cf. ~amson et al., 1976: 37-40). PenicilIium casei Staub vat. compactum Abe. - - J. Gen. Appt. Microbiol. (Tokyo) 2: 101. 1956. Penicillium pseudocasei Abe. - - J. Gen. Appl. Microbiol. (Tokyo) 2 : 102. 1956; ex G. Smith - Trans. Br. Mycol. Soc. 46: 335. 1963. PENICILLIUM SPECIES FROM FERMENTED CHEESES 345 Peniciltium roqueforti Thorn vat. p u n c t a t u m Abe - - J. Gen. Appl. Microbiol. (Tokyo) 2: 99. 1956. These three taxa were not validly described, because they lacked a Latin diagnosis. After examination of the type cultures Samson et al. (1976) regarded these 3 species as synonyms of P. verrucosum var. cyctopium. Penicillium roqueforti T h o r n . - Bull. Bur. Anim. Ind. U.S. Dep. Agric. 82: 35. 1906. - P e n i c i l l i u m aromaticum casei J o h a n - O l s e n . - - Zentbl. Bakt. P a r a s i t K d e Abt. II. 4: 164. 1898. ? Penicillium atroviride Dierckx. A n n . Soc. Scient. Brux. 25: 87. 1901. - Penicitlium vesiculosum Bain. - - Bull. Soc. Mycol. Fr. 23: 10. 1907. PeniciIlium roqueforti T h o r n var. weidemannii Westling. - - Ark. Bot. 11: 52. 1911. - Penicillium atroviride Sopp. Vidensk Selsk. Skr. Krlstiana, m a t . - n a t u r v . K1.11 : 149. 1912 (non P. atroviride Dierckx). Penicillium aromaticum S o p p . - ibid. 11: 155. 1912. - Penicillium roquefort Sopp. - - ibid. 11 : 156. 1912. - Penicillium gorgonzola Weidemann apud Biourge. Cellule 33: 204. 1923. Penicitlium stilton Biourge. - - Cellule 33: 206. 1923. Penieittium suaveolens Biourge. - - CelluIe 33: 200. t923. Penicillium biourgei Arnaudi. - - ZentbI. Bakt. ParasitKde, Abt. If. 73: 321. 1928. - Colonies on Czapek agar growing rapidly, attaining a diameter of 4--5 cm within 14 days at 25 C, consisting of a dense felt of erect conidiophores; in fresh isolates typically velvety without production of aerial mycelium; in older cultures becoming more tanose with production of aerial vegetative mycelium. Colour blue-green near Pois or Leaf green (Ridgway, 19t2. pl. 41), later becoming darker. Exudate in fresh isolates often present as hyaline droplets. Odour mostly absent or not pronounced. Reverse greenish, often changing to darker shades of green to black. Conidiophores two- or three-stage branched, 100 200 #m tall and 4-6.5 #m wide, the stipe typically ornamented with conspicuous warts, some strains less roughened at the apex of conidiophore stipes, but usually ornamentated at the base. Metulae 10-15 x 3-4.5 #m, roughwalled, giving rise to dusters of 4-7 phialides. Phialides flask-shaped with short neck, 8-12 × 3.0-3.5 #m. Conidia in loose columns, globose to subglobose, greenish, smooth-walled, mostly 4-6 #m, occasionally up to 8 #m (Fig. 2). Reduced conidiogenous structures occur submerged in the agar. The conidiophore is frequently branched (see Fig. 3) in a manner slightly resembling the branching pattern of the Divaricata. The ornamentation is sometimes less pronounced. Phialides are slightly larger and less uniform in shape. Conidia are produced in short chains and are mostly larger than those produced by aerial conidiophores. Sclerotia are often formed in old cultures which usually also produce some aerial vegetative hyphae. The sclerotia are white, soft, 50-100 gm in diameter, and consist of a loose thin knit of hyphae. The sclerotium centre consists of a pseudoparenchymatic cell mass. 346 R. A . SAMSON, C. ECKARDT AND R. ORTH Fig. 2. Penicillium roqueforti, conidiophores and conidia. Colonies on m a l t a g a r similar in g r o w t h a n d c o l o u r b u t the texture is thinner. C o n i d i o g e n o u s structures are identical to those o n C z a p e k agar, b u t the o r n a m e n t a t i o n o f the c o n i d i o p h o r e stipe is usually m o r e p r o n o u n c e d . Material examined: CBS 221.30 = NRRL 849 = ATCC 10110 = IMI 24313, type culture of P. roqueforti, isolated from roquefort cheese by C. Thom. Fig. 3. Penicillium roqueforti, conidiogenous structures in submerged agar. PENICILLIUM SPECIES FROM FERMENTED CHEESES 347 CBS 234.38, isolatedfrom btue Cheshirecheeseand sent by S. Dattilo-Rubbo,probablytype culture of P. roqueforti var. viride. Numerous other isolates from French, Itatien, German, English and Danish Blue cheeses but also from meat products, bread, ice cream, and other food products. This material also includes isolatesdescribed by Frank (1966). Discussion P. roqueforti can be easily recognized by its fast growth, its dark blue-green, velvety colonies and the wide, warted conidiophore stipes. The species has sometimes been confused with velvety forms of P. verrucosum var. cyclopium, but this fungus usually has smaller conidia and thinner conidiophore stipes with smaller protuberances. In addition, the colonies of P. verrucosum var. cyclopium typically produce strong earthy or streptomyces-like odours, while colonies of P. roqueforti are odourless. Raper and Thorn (1949) did not describe sclerotial development in P. roqueforti strains, and we were unable to find mention of sclerotium development by this species in the literature. Sclerotia were often found in old colonies (3 weeks and older) and hence they were probably not observed by previous authors. Although P. roqueforti has normally blue-green colonies, we have encountered one brown strain which agrees exactly in its microscopic characters. This strain (CBS 501.75 = IMI 54229) was isolated from barley grains and probably represents a natural colour 'mutant. Knight, Mohr and Frazier (1950) and Morris, Jezeski and Combs (1954) reported white mutants of P. roqueforti obtained by irradiation with UV light of a normal green strain. These mutants proved to be of value in cheese manufacture, because of the similar enzymatic and growth characters. Knight et al. (1950) also suggested that one gene is probably responsible for the green pigmentation of the conidia. Occurrence and toxicology of P. camemberti and P. roqueJorti In addition to being used for the production of fermented cheeses, P. carnemberti and P. roqueforti also occur on other substrates. Jirkovsky and Galg6czy (1966) reported that 61~ of the fungal isolates from Hungarian salami proved to be P. camemberti. P. roqueforti is one of the common microorganisms in fermented silage (Raper and Thorn, 1949 ; Le Bars and Escoula, 1974), meat products (Leistner and Ayres, 1967; Racovita, Racovita and Constantinescu, 1969; Hadlok, Samson and Schorr, 1975) and other food products. Mycotoxicoses by P. roqueforti have been reported by Kanota (1970), Still et al. (1972) and Lafont et al. (1976). Toxic substances have been isolated and incompletely characterized by Kanota (1970). Wei et al. (1973, 1975) isolated a "PR-toxin" from P. roqueforti culture media, a sesquiterpenoid metabolite, and Polonelli et al. (1975), Moreau et al. (1976) and Orth (1976) confirmed these findings. Alkaloids have been isolated and characterized by Taber and Vining (1958), 348 R. A. SAMSON, C. ECKARDT AND R. ORTH A b e et al. (1967), B e k m a k h a n o v a (1974), O h o m o et al. (1975), Scott, M e r r i e n a n d P o l o n s k y (1976) a n d Scott a n d K e n n e d y (1976), a n d one of these, r o q u e fortine A, proved to be weakly toxic ( O h o m o et al., 1975). L o n g - t e r m feeding experiments with r a i n b o w trouts ( F r a n k et al., 1975) a n d rats ( F r a n k et al., 1977) using P, c a m e m b e r t i a n d P. r o q u e f o r t i have, however, n o t revealed any evidence of carcinogenic or other pathogenic effects. This work was completed d u r i n g tenure of a N A T O Science Fellowship at the C e n t r a a l b u r e a u voor Schimmelcultures, Baarn, awarded to C. E c k a r d t by the D . A . A . D . ( G e r m a n A c a d e m i c Exchange Service). We t h a n k Professor Dr. H. K. F r a n k for the P e n i c i l l i u m cultures used in the present study. R e c e i v e d 9 J u n e 1977 REFERENCES ABE, M., YAMATODANI,S., YAMANO,T., Kozu, Y and YAMADA,S. 1967. Production of alkaloids and related substances by fungi. I. Examination of fungi for their ability of producing ergot alkaloids. - - J. Agric. Chem. Soc. Japan. 41 : 68-71. Anon. 1874. Mikroorganismen ftir Lebensmitteltechnik. 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