Prediction and optimization of the laccase-mediated synthesis of the antimicrobial compound iodine (I2).

An artificial neural network (ANN) and genetic algorithm (GA) were applied to improve the laccase-mediated oxidation of iodide (I(-)) to elemental iodine (I2). Biosynthesis of iodine (I2) was studied with a 5-level-4-factor central composite design (CCD). The generated ANN network was mathematically evaluated by several statistical indices and revealed better results than a classical quadratic response surface (RS) model. Determination of the relative significance of model input parameters, ranking the process parameters in order of importance (pH>laccase>mediator>iodide), was performed by sensitivity analysis. ANN-GA methodology was used to optimize the input space of the neural network model to find optimal settings for the laccase-mediated synthesis of iodine. ANN-GA optimized parameters resulted in a 9.9% increase in the conversion rate.

Protection of wood from microorganisms by laccase-catalyzed iodination.

In the present work, Norway spruce wood (Picea abies L.) was reacted with a commercial Trametes versicolor laccase in the presence of potassium iodide salt or the phenolic compounds thymol and isoeugenol to impart an antimicrobial property to the wood surface. In order to assess the efficacy of the wood treatment, a leaching of the iodinated and polymerized wood and two biotests including bacteria, a yeast, blue stain fungi, and wood decay fungi were performed. After laccase-catalyzed oxidation of the phenols, the antimicrobial effect was significantly reduced. In contrast, the enzymatic oxidation of iodide (I(-)) to iodine (I(2)) in the presence of wood led to an enhanced resistance of the wood surface against all microorganisms, even after exposure to leaching. The efficiency of the enzymatic wood iodination was comparable to that of a chemical wood preservative, VP 7/260a. The modification of the lignocellulose by the laccase-catalyzed iodination was assessed by the Fourier transform infrared spectroscopy-attenuated total reflectance (FTIR-ATR) technique. The intensities of the selected lignin-associated bands and carbohydrate reference bands were analyzed, and the results indicated a structural change in the lignin matrix. The results suggest that the laccase-catalyzed iodination of the wood surface presents an efficient and ecofriendly method for wood protection.

Efficient production of Al(OH)3-immobilized laccase with a Heterobasidion annosum strain selected by microplate screening.

AIMS: Wild-type white rot fungi are the most important production organisms for laccase, a promising oxidative biocatalyst with numerous applications. This study aimed at identifying novel highly productive strains, finding optimal cultivation conditions for laccase production and establishing a simple immobilization procedure. METHODS AND RESULTS: By using a newly developed 96-well microplate cultivation method, 23 species of white rot fungi, represented by 29 strains, were directly compared with regard to the amount of secreted laccase. Both, with glucose and spruce saw dust as growth substrate a Heterobasidion annosum strain and a Physisporinus vitreus strain were the most productive (730­2200 U l−1 of secreted laccase). Cultivation conditions for laccase production with H. annosum were optimized in larger-scale liquid cultures. Aeration with a sparger lead to a 3·8-fold increase in laccase activity when compared to nonaerated flask cultures. More than 3000 U l−1 laccase was produced in glucose medium supplemented with yeast extract and the inducer veratryl alcohol. Culture supernatant was incubated with short-range ordered Al(OH)3 particles to directly immobilize and concentrate laccase by adsorption. Active laccase was recovered in 40% yield and the Al(OH)3-adsorbed laccase was suitable for repeated decolourization of indigo carmine. CONCLUSIONS: Microplate cultivation allowed a large-scale comparison of the capacity of different fungal species for laccase production. Laccase secretion of a highly productive H. annosum strain was found to vary strongly with different cultivation conditions. Adsorption to Al(OH)3 proved to be suitable as direct immobilization technique.