Light-induced inhibition of laccase in Pycnoporus sanguineus.

The aim was to determine which specific regions of the visible light spectrum were responsible for the induction or inhibition of laccase in Pycnoporus sanguineus. Cultures were exposed to various bandwidth lights: blue (460 nm), green (525 nm), white (a combination of 460 and 560 nm), red (660 nm), and darkness. The results indicate that short wavelengths strongly inhibit the production of laccase: green (3.76 ± 1.12 U/L), blue (1.94 ± 0.36 U/L), and white (1.05 ± 0.21 U/L) in proportions of 85.8, 92.6, and 96.0%, respectively; whereas long wavelengths inhibit laccase production only partially i.e., red light (14.05 ± 4.79 U/L) in a proportion of 46.8%. Maximum activity was induced in absence of visible light (30 °C, darkness), i.e., 30.76 ± 4.0 U/L. It is concluded that the production of laccase in P. sanguineus responds to light stimuli [measured as wavelengths and lx] and that it does so inversely. This can be explained as an ecological mechanism of environmental recognition, given that P. sanguineus develops inside lignocellulose structures in conditions of darkness. The presence of short wavelength light (460-510 nm) would indicate that the organism finds itself in an external environment, unprovided of lignin, and that it is therefore unnecessary to secrete laccase. This possible new regulation in the laccase production in P. sanguineus has important biotechnological implications, for it would be possible to control the production of laccase using light stimuli.

Ethanol induction of laccase depends on nitrogen conditions of Pycnoporus sanguineus

Background Ethanol has been pointed out as a laccase inducer. However, there are controversial reports about its efficiency with some fungi. In this study, we hypothesized that ethanol laccase induced in Pycnoporus sanguineus depends on nitrogen nutriment conditions. To prove this, we assessed laccase production in submerged cultures of P. sanguineus, with different nitrogen concentrations and with, or without ethanol added in a factorial designed experiment. Results In order to analyze the effects of factors on the response variables, a factorial ANOVA, and response-surface models were performed. It was found that the nitrogen source was the main factor that affected laccase production in P. sanguineus. The treatments with yeast extract (2 g/L) and ethanol (3 g/L) induced the highest laccase activity (31.01 ± 4.9 U/L), while the treatments with urea reached the lowest activity (less than 1.6 U/L). Ethanol had positive and synergic effects on laccase production, in accordance with the surface response model, as long as simple nitrogen sources (urea) were not available. Conclusions We suggest that laccase in P. sanguineus is regulated by a catabolic nitrogen repression mechanism; laccase activity is strongly inhibited by urea used as nitrogen source and it decreases when the amount of urea increases; contrarily, a synergic positive effect was observed between yeast extract and ethanol on laccase production.