Frases Susana, Salazar Angela, Dadachova Ekaterina, Casadevall Arturo
Department of Microbiology and Immunology, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
Appl Environ Microbiol. 2007 Jan;73(2):615-21. doi: 10.1128/AEM.01947-06. Epub 2006 Nov 10.
Cryptococcus neoformans melanizes in the environment and in mammalian tissues, but the process of melanization in either venue is mysterious given that this microbe produces melanin only from exogenous substrates. Understanding the process of melanization is important because melanization is believed to protect against various stresses in the environment, including UV radiation, and pigment production is associated with virulence. Melanization in C. neoformans requires the availability of diphenolic precursors. In contrast, many bacteria synthesize melanin from homogentisic acid (HGA). We report that C. neoformans strains representing all four serotypes can produce a brown pigment from HGA. The brown pigment was acid resistant and had the electron paramagnetic resonance spectrum of a stable free radical, qualities that identified it as a melanin. Melanin "ghost"-like particles obtained from pigmented C. neoformans cells were hydrophobic, fluorescent under a variety of irradiation wavelengths, negatively charged, insoluble in organic solvents and alcohols, resistant to degradation by strong acids, and vulnerable to bleaching. HGA melanization was laccase dependent and repressed by high concentrations of glucose. The ability of C. neoformans to utilize a bacterial melanin precursor compound suggests a new substrate source for melanization in the environment.
新型隐球菌在环境和哺乳动物组织中会发生黑化，但鉴于这种微生物仅从外源性底物产生黑色素，在这两种环境中的黑化过程都很神秘。了解黑化过程很重要，因为黑化被认为可抵御环境中的各种压力，包括紫外线辐射，而且色素产生与毒力相关。新型隐球菌的黑化需要二酚类前体的存在。相比之下，许多细菌从尿黑酸（HGA）合成黑色素。我们报告称，代表所有四种血清型的新型隐球菌菌株都能从HGA产生一种棕色色素。该棕色色素耐酸，具有稳定自由基的电子顺磁共振光谱，这些特性将其鉴定为黑色素。从有色素的新型隐球菌细胞获得的黑色素“幽灵”样颗粒具有疏水性，在各种照射波长下都能发出荧光，带负电荷，不溶于有机溶剂和醇类，耐强酸降解，且易被漂白。HGA黑化依赖漆酶，并受到高浓度葡萄糖的抑制。新型隐球菌利用细菌黑色素前体化合物的能力表明环境中黑化有了新的底物来源。
