Enhancement of Dichomitus squalens tolerance to copper and copper-associated laccase activity by carbon and nitrogen sources

This study revealed a dual effect of copper on D. squalens laccase activity, inducing and suppressing. The addition of copper sulfate led to enhancement of the enzyme activity until it reached a maximum value at peak copper sulfate concentration (PC) followed by suppression and even complete termination of the enzyme activity. Maximum laccase yield is a function of fungi tolerance and media composition. Nutrients had a significant impact on copper-independent and copper-induced laccase activity. Some nutrients also improved tolerance of cells and laccase-producing system to copper load. The effect of specific nutrient depended on the ratio of carbon and nitrogen sources. This research can be used to predict the effective copper concentration and nutrient composition to stimulate the laccase production without compromising the fungi growth. The methylated substrates (3-O-methylglucose, methylcellulose) in combination with casein and copper demonstrated high potential to support fungi tolerance and enhanced laccase activity.

► Copper has a dual effect on laccase activity, inducing and suppressing.
► Copper for maximum laccase activity depends on carbon/nitrogen sources and their ratios.
► Laccase suppression and eradication due to copper depends on nutrients.
► There are two types of copper toxicity: growth-related and laccase-related.
► Casein reduces growth related copper toxicity and enables high laccase activity.