Characterization of melanin pigment produced by Aspergillus nidulans.

Although most of the Ascomycetes present DHN-melanin, some reports suggest that A. nidulans does not produce this type of melanin. In this study, we analyzed the pigment extracted from highly melanized strains (MEL1 and MEL2) of Aspergillus nidulans to determine the type of melanin present in this fungus. Our results showed that the pigment produced by MEL1 and MEL2 mutants possesses physical and chemical properties and UV- and IR-spectra very similar to synthetic DOPA-melanin. The characterization of this pigment in terms of its degradation products indicated the presence of indolic units, which were also found in synthetic DOPA-melanin. The analyses of the elemental composition showed that the pigment extracted from these mutants has a high percentage of nitrogen and, therefore, it cannot be DHN-melanin, which presents only trace of nitrogen. This observation was confirmed in the test with tricyclazole because this inhibitor of DHN-melanin biosynthesis did not suppress pigment production in the MEL1 and MEL2 strains. On the other hand, in a medium containing tropolone, an inhibitor of DOPA-melanin biosynthesis, the dark pigmentation of the colonies was not observed indicating that this compound inhibited melanin production in these strains. Taken together, the results obtained in this study indicate that melanin produced by these mutants is DOPA type, representing the first report on characterization of this type of melanin in A. nidulans.

Advances and developments in strategies to improve strains of Saccharomyces cerevisiae and processes to obtain the lignocellulosic ethanol--a review.

The conversion of biomass into ethanol using fast, cheap, and efficient methodologies to disintegrate and hydrolyse the lignocellulosic biomass is the major challenge of the production of the second-generation ethanol. This revision describes the most relevant advances on the conversion process of lignocellulose materials into ethanol, development of new xylose-fermenting strains of Saccharomyces cerevisiae using classical and modern genetic tools and strategies, elucidation of the expression of some complex industrial phenotypes, tolerance mechanisms of S. cerevisiae to lignocellulosic inhibitors, monitoring and strategies to improve fermentation processes. In the last decade, numerous engineered pentose-fermenting yeasts have been developed using molecular biology tools. The increase in the tolerance of S. cerevisiae to inhibitors is still an important issue to be exploited. As the industrial systems of ethanol production operate under non-sterile conditions, microbial subpopulations are generated, depending on the operational conditions and the levels of contaminants. Among the most critical requirements for production of the second-generation ethanol is the reduction in the levels of toxic by-products of the lignocellulosic hydrolysates and the production of low-cost and efficient cellulosic enzymes. A number of procedures have been established for the conversion of lignocellulosic materials into ethanol, but none of them are completely satisfactory when process time, costs, and efficiency are considered.

Kinetic studies of nitrite uptake by Aspergillus nidulans.

1. In the filamentous mold Aspergillus nidulans, net nitrite uptake is inducible by nitrate and nitrite, is probably different from the nitrate uptake system and is partially repressed by ammonium. 2. The concentration dependence of net nitrite uptake by the biA1 facA303 strain of A. nidulans shows a saturation kinetics with an apparent Km value of 0.64 mM. 3. Strains of A. nidulans carrying the nihA1 and nihA1 chlA14 mutations considerably reduced the affinity of the nitrite uptake system for the substrate when nitrite concentrations ranging from 2.5 mM to 10.0 mM were tested (apparent Km values of 5.9 mM and 23.6 mM, respectively). 4. These results suggest that the toxic effect of nitrite on A. nidulans is due to enhanced nitrite uptake by nihA strains when high concentrations are present in the medium.

Kinetic studies of nitrite uptake by Aspergillus nidulans

1. In the filamentous mold Aspergillus nidulans, net nitrite uptake is inducible by nitrate and nitrite, is probably different from the nitrate uptake system and is partially repressed by ammonium. 2. The concentration dependence of net nitrite uptake by the biA1 facA303 strain of A. nidulans shows a saturation kinetics with an apparent Km value of 0.64 mM. 3. Strains of A. nidulans carrying the nihA1 and nihA1 chlA14 mutations considerably reduced the affinity of the nitrite uptake system for the substrate when nitrite concentrations ranging from 2.5 mM to 10.0 mM were tested (apparent Km values of 5.9 mM and 23.6 mM, respectively). 4. These results suggest that the toxic effect of nitrite on A. nidulans is due to enhanced nitrite uptake by nihA strains when high concentrations are present in the medium