Role of ethanol on growth, laccase production and protease activity in Pycnoporus cinnabarinus ss3

Laccase production by the strain Pycnoporus cinnabarinus ss3 was studied in a solid-state culture on sugar-cane bagasse using chemical compounds as inducers (ethanol, methanol, veratryl alcohol and ferulic acid). Laccase productions were about 5- to 8.5-fold higher than non-induced cultures. Liquid-culture experiments with 14C-labeled ethanol were conducted. Ninety-eight percent of the initial amount of 14C from ethanol was recovered as 14CO 2, 14C-biomass and soluble 14C-compounds (mainly ethanol). The amount of 14C in the biomass was only 6.8% of the total carbon consumed by P. cinnabarinus, in absence of maltose, representing only 2.8% of added ethanol (1.1% and 1.6% in presence of maltose, respectively). Ethanol was poorly used as carbon and energy sources for P. cinnabarinus growth and other carbon sources present in the liquid medium (yeast extract and sodium tartrate) were preferentially degraded. Time-courses of laccase activity and gene expression were monitored in column in presence or in absence of ethanol vapors. Analyses showed a perfect correlation between the activity and the amount of transcript. After 16 days of ethanol ventilation through the column, the ethanol flow was stopped. Immediately, both laccase activity and gene expression decreased, but started to increase again as soon as the ventilation was restored. In parallel, the effect of ethanol on protease activity in P. cinnabarinus was measured. Presence of ethanol led to an inhibition of protease activity. Therefore ethanol plays a regulatory role on two elements (gene-expression and protease-activity levels) that are both in favor of an increase in laccase production by the fungus.