Heat stress on Fomes culture reduces proteases and improves laccases thermostability

The aim of this work was to study the production of laccase and protease activity by Fomes sp. EUM1 under heat stress when a temperature shift from 35 to 45°C was applied. The highest values of laccase activity were similar and obtained after the temperature shift, 76 and 81.6 U/ gram of initial dry substrate (gids) at 35 and 45 °C respectively.  For protease activity, at 35°C the peak activity (6.4 U/gids) was obtained at day 7 and maintained until the end of the culture and at 45°C the peak activity (4.3 U/gids) was obtained when the temperature shift was realized (day 6) and decreased until the end of the culture. In the zymogram of laccase activity one band with a molecular weight of 45 kDa was observed with extracts from both temperatures evaluated with slight differences in molecular weight and intensity of the bands at the various days assessed. The thermostability of the laccases and proteases produced was evaluated, at the highest temperature assessed (60°C) for laccase activity the inactivation constant was 0.324 h^-1 and 0.277 h^-1 from cultures at 35 and 45 °C, respectively. These results showed that a temperature shift from 35 to 45°C in the culture of Fomes sp. EUM1 increases laccases thermostability and decreases proteases production and thermostability.

Keywords: Fomes, laccase, protease, thermostability.