Tailoring a mycelium-bound lipase activity by submerged fermentation using Aspergillus niger MYA 135: Culture medium optimization

REGNER, ERIKA LUCÍA; SALVATIERRA, NATALIA HEBE; CANAL, VERÓNICA; BAIGORI, MARIO DOMINGO; PERA, LICIA MARÍA

San Miguel de Tucumán

Congreso; XII Congreso Argentino de Microbiología General; 2017

SAMIGE

Lipases (EC 3.1.1.3) are important industrial enzymes due to their versatile applications. They catalyze a variety of reactions such as hydrolysis, esterification, transesterification and interesterification. In addition,the biocatalyst design by using the medium engineering strategy is an alternative way to obtain catalytic efficiency and specific characteristics like substrate specificity, stability, etc. In this sense, the application of statistically-based assays such as the central composite design (CCD) becomes a powerful tool. Previously, among eleven variables, the carbon/nitrogen ratio and the concentration of both olive oil and FeCl3 were identified as significant parameters for the production a mycelium-bound lipase activity from Aspergillus niger MYA 135. The aim of this work was to tune this whole-cell biocatalyst bysubmerged fermentation using a CCD. Thus, the level of those important input factors was optimized to maximize the lipase production. All experiments were performed in duplicate and analyzed with the Minitab software for Windows. The hydrolytic activity was measured with p-nitrophenyl palmitate (C16) as substrate. The molar extinction coefficient of p-nitrophenol (p-NP) under the given assay conditions was 0.00979 μM-1 cm-1. One unit of enzyme activity (U) was defined as the amount of biocatalyst that released 1 μmol of p-NP per min. Specific activity was expressed as U per gram of mycelium dry weight. As a result, the optimal culture conditions were the following: 1.63 % olive oil (X1), 0.08 g/l FeCl3 (X2) and a carbon/nitrogen ratio (X3) of 0.24. Under these conditions the mycelium-bound lipase activity was 2.04 ± 0.13 U per gram of dry weight. The effect of each variable was also analyzed; the linear coefficient of X3, all interaction terms coefficients and the quadratic coefficients of X12, X22 and X32 were significant, as their P values were below 0.05. In addition, the P-value for the lack-of-fit test (0.118) showed the adequacy of the obtained model. This is also verified by the R2 (98.25 %) and the Adj R2 (97.56 %) coefficients indicating the percentage of variability that is explained by the model. In conclusion, the response surface methodology was successfully used to increase the production of a mycelium-bound lipase six times. Finally, the performance of these biocatalysts in the biodiesel synthesis was also discussed. This work was supported by FONCyT (PICT 2011-2158 and PICT 2015- 2596), CONICET (PIP 339) and UNT (PIUNT E548/3).