Laccase and Melanization in Clinically Important Cryptococcus Species Other than Cryptococcus neoformans

Abstract

The laccase enzyme and melanin synthesis have been implicated as contributors to virulence in Cryptococcus neoformans. Since isolations of Cryptococcus species other than C. neoformans from clinical specimens have been increasing, we examined the laccase activities of C. albidus, C. laurentii, C. curvatus, and C. humicola. Incubation of cells with epinephrine produced adrenochrome color in C. albidus, C. laurentii, and C. curvatus but not in C. humicola. Activity was always less than in C. neoformans. Laccase was detected in the soluble fractions of disrupted C. albidus, C. laurentii, and C. curvatus cells. Activity staining of partially purified enzyme after nondenaturing polyacrylamide gel electrophoresis revealed that laccases from C. albidus, C. laurentii, and C. curvatus migrated more slowly than that from C. neoformans. One strain of C. curvatus exhibited two melanin bands. Thus, several clinically emerging Cryptococcus species express laccase and can synthesize melanin.Cryptococcosis is a life-threatening infection that complicates a variety of immunocompromising conditions (4). Although 34 species of the genus Cryptococcus are recognized (6), C. neoformans is generally considered to be the pathogenic species, while C. albidus, C. laurentii, and C. curvatus have been regarded as saprophytic species. However, species other than C. neoformans have, in fact, been isolated from normally sterile clinical specimens. We note isolations of C. albidus in septicemia and meningitis (15,22,23), C. laurentii in fungemia (14,19) and meningitis (15), C. curvatus in myeloradiculitis (5), and C. humicola in meningitis (28), all in patients with AIDS or cancer. Thus, cryptococcosis due to species other than C. neoformans may be considered an emerging infection.The virulence of C. neoformans has been ascribed to capsule formation, melanization due to laccase (phenoloxidase), proteinase secretion, and phospholipases (3). Although many pathogenic fungi synthesize precursors of melanin, melanization in C. neoformans occurs when exogenous or environmental catechols or aminophenols are oxidatively polymerized by the laccase enzyme and deposited as melanin in the cell wall (1, 26). Melanization has often been used for the identification of isolates, since growth of brown colonies on birdseed agar made from Guizotia abyssinica, or thistle seeds rich in caffeic acid, is characteristic of C. neoformans (29). However, we noted that several strains of species other than C. neoformans produced light-brown colonies on this medium or on defined medium containing synthetic substrates. In this study, we examined laccase enzymes and melanization in cryptococcal species other than C. neoformans. MATERIALS AND METHODSStrains used. The strains used in this study are listed in Table 1 as accessed in the culture collections Centraalbureau voor Schimmelcultures (CBS) and Japan Collection of Microorganisms (JCM). The strains were obtained from each institute directly and maintained on YM agar (Difco) slants. Some of the strains have recently been ...

Dual Infections with Pigmented and Albino Strains ofCryptococcus neoformansin Patients with or without Human Immunodeficiency Virus Infection in India

“…First, it was essential to demonstrate that the isolates were C. neoformans rather than other yeasts. In this regard, other Cryptococcus species, such as C. albidus, C. laurentii, and C. curvatus, have been reported to rarely cause human infection (reviewed in reference 3), and these species have the capacity to express laccase and synthesize melanin (19). Spontaneous melanin-deficient mutants can occur in the laboratory (35), and melanin-deficient C. neoformans has been reported in human cryptococcosis (40).…”

Senescence of the Lentinula edodes Fruiting Body After Harvesting

“…There are many reports in the literature of the purification and characterization of Lcc isoforms from white-rot fungi, and several Lccencoding genes have been isolated (reviewed by Kumar et al, 2003;Baldrian, 2006). A correlation between melanin synthesis and intracellular Lcc in Cryptococcus neoformans has been reported (Ikeda et al, 2002). Lcc in Aspergillus nidulans is considered to form L-DOPA to synthesize melanins in conidia (Aramayo and Timberlake, 1990).…”

Systemic Cryptococcus Albidus Infection in a Doberman Pinscher

“…15 The brown pigment from C. neoformans is owing to the production of melanin, which may be an important virulence factor. 6 Some strains of C. albidus have shown melanin production in smaller amounts, with colonies appearing as light brown. 6 Commercial yeast identification systems may be used to identify these organisms.…”

“…6 Some strains of C. albidus have shown melanin production in smaller amounts, with colonies appearing as light brown. 6 Commercial yeast identification systems may be used to identify these organisms. 15 The clinical diagnosis of cryptococcal infection generally relies on a serological test that uses an antigen latex agglutination assay.…”

“…4 In humans, C. albidus has been associated with meningitis 11 , skin infection 12 , pulmonary infection 17 , mucormycosis empyema, osteomyelitis, and septicemia. [5][6][7][8][9][10] In each case, patients were immunocompromised by other diseases such as HIV.…”