Brown- and Red-Pigmented Pseudomonas Aeruginosa: Differentiation Between Melanin and Pyorubrin

Abstract

PLATE XI1WE have recently isolated from clinical material three strains of Pseudomonas aeruginosa that produced a brown pigment which diffused through agar. Pigmentation varied in intensity from light brown to a deep coffee colour. Perusal of several standard microbiology textbooks and a survey of the literature left us uncertain whether this pigment was one of those occasionally produced by P. aeruginosa, namely pyorubrin and pyomelanin. Consequently, we sought to obtain for comparative purposes strains of this species authenticated as producers of one or other of these pigments. It soon became apparent, however, that some of the characteristics attributed to certain standard strains from the National Collection of Type Cultures (NCTC) were in this respect misleading, and it was not until we had obtained further reference strains from Japan that we were able to define our pigment categorically.The appearance in culture of P. aeruginosa strains that produce red pigment have been described by some observers simply as " r e d " (Meader, Robinson and Leonard, 1925;Wahba, 1965) and by others as yellowish turning gradually to red (Gessard, 1920;Holliman, 1961 ;Narano, 1965). The appearance is certainly strongly dependent upon cultural conditions and the production of other pigments (Simon, 1956). The position is complicated by the fact that acidification of pyocyanin produces a red colour, and that exposure of plates containing pyocyanin to light and air for some time (8 days, in our hands) produces a light brown colour. Some authorities, indeed, appear to regard all red and brown pigments of P. aeruginosa as oxidation products of pyocyanin (Leonard, 1924;Wilson and Miles, 1964). The frequency of red strains among clinically isolated specimens is low; Wahba (1965) reported 350/,--more than half obtained from infected urines; and Phillips (1969) found 6%.The cultural appearance of strains of P. aeruginosa that produce brown pigment is also dependent upon the nature of the medium. It has been described variously as "coffeebrown " (Yabuuchi and Ohyama, 1972), "brown, dark brown or black " (Elston, 1968) and " rouge-brun " (Gessard, 1920). Some strains have also been referred to merely as being " melanogenic " (Gessard, 1925;Espinosa, Portoles and Hidalgo, 1970). The frequency of so-called brown strains among clinically isolated P. aeruginosa has been variously assessed as 2.5 % (Elston, 1968), 10-5 % (Wahba, 1965) and < 1 % (Phillips, 1969).It is clear from the above that there may be considerable difficulty in deciding whether a light mahogany shade, such as that produced by our strains on Sensitivity-Test Agar (especially after a short period of incubation) should best be described as " reddish brown " (ie., pyorubrin) or " light brown " (i.e., pyomelanin). We have also observed that several experienced microbiologists were erroneously under the impression that melanin is black, as opposed to dark brown. This is hardly surprising in view of the derivation of the word (Greek, pAag = black); further, melanin is describe...

Melanins: Skin Pigments and Much More—Types, Structural Models, Biological Functions, and Formation Routes

“…Nowadays, the polymer is considered allomelanin although the original paper doubted about the melanin-like nature of that product as it was formed without the involvement of a polyphenol oxidase [138]. Similar data were reported with some Pseudomonas [142,143] due to a reduced 4-hydroxyphenylpyruvate dioxygenase activity, and the pigment is considered pyomelanin [144].…”

Self-generated diversity produces “insurance effects” in biofilm communities

“…Pyomelanin production was detected on plates containing 0.7% K 2 HPO 4 , 0.3% KH 2 PO 4 , 0.05% trisodium citrate, 0.01% MgSO 4 , 0.1% (NH 4 ) 2 SO 4 , 0.2% glucose, and 1% L-tyrosine (26). Auxotrophs were detected by stamping colonies from TSB plates onto minimal salts medium plates with 0.2% glucose (27).…”

Cyst production and brown pigment formation in aging cultures of Azospirillum brasilense ATCC 29145

“…This pigment appears to be melaninlike according to preliminary tests performed as suggested for any melanin pigment (25,27,46). Production of melanin pigments by bacteria has been reported for species within several genera, including Rhizobium (6, 7), Pseudomonas (13,30), Micrococcus (27), Gluconobacter (34), Mycobacterium (36), and Azotobacter (41). The brownish black pigment exhibited in most bacteria has been partially characterized and suggested to be melanins (18).…”