This research aimed to establish the relationship between carbon–nitrogen nutritional factors and copper sulfate on laccase activity (LA) by Pleurotus ostreatus. Culture media composition was tested to choose the nitrogen source. Yeast extract (YE) was selected as a better nitrogen source than ammonium sulfate. Then, the effect of glucose and YE concentrations on biomass production and LA as response variables was evaluated using central composite experimental designs with and without copper. The results showed that the best culture medium composition was glucose 45 gL⁻¹ and YE 15 gL⁻¹, simultaneously optimizing these two response variables. The fungal transcriptome was obtained in this medium with or without copper, and the differentially expressed genes were found. The main upregulated transcripts included three laccase genes (lacc2, lacc6, and lacc10) regulated by copper, whereas the principal downregulated transcripts included a copper transporter (ctr1) and a regulator of nitrogen metabolism (nmr1). These results suggest that Ctr1, which facilitates the entry of copper into the cell, is regulated by nutrient-sufficiency conditions. Once inside, copper induces transcription of laccase genes. This finding could explain why a 10–20-fold increase in LA occurs with copper compared to cultures without copper when using the optimal concentration of YE as nitrogen sources.

This research aimed to establish the relationship between carbon-nitrogen nutritional factors and copper sulfate on laccase activity (LA) by Pleurotus ostreatus. Culture media composition was tested to choose the nitrogen source. Yeast extract (YE) was selected as a better nitrogen source than ammonium sulfate. Then, the effect of glucose and YE concentrations on biomass production and LA as response variables was evaluated using central composite experimental designs with and without copper. The results showed that the best culture medium composition was glucose 45 gL-1 and YE 15 gL-1, simultaneously optimizing these two response variables. The fungal transcriptome was obtained in this medium with or without copper, and the differentially expressed genes were found. Main up-regulated transcripts included three laccase genes (lacc2, lacc6, and lacc10) regulated by copper, whereas the principal down-regulated transcripts included a copper transporter (ctr1) and a regulator of nitrogen metabolism (nmr1). These results suggest that Ctr1, which facilitates the entry of copper in the cell, is regulated by nutrient-sufficiency conditions. Once inside, copper induces transcription of laccase genes. This finding could explain why a 10 to 20-fold increase in LA occurs with copper compared to cultures without copper when using the optimal concentration of YE as nitrogen sources.

• Metabolites extracted from Cordyceps nidus induce laccase activity of Pleurotus ostreatus. • The composition of the substrate where Cordyceps nidus is grown induces the production of different bioactive compounds. • Laccase activity of P. ostreatus is improved four times over the control condition when C. nidus’ extracts are supplemented. • The addition of C. nidus’ extracts to the cultures of P. ostreatus improves the production of fermentable sugars.

This study aims to optimize the bioconversion of palm kernel cake (PKC) by Pleurotus ostreatus to improve fungal biomass production, lignocellulolytic enzyme expression, and the nutritional value of the substrate as ruminant feed. Three inorganic nitrogen sources (ammonium sulfate, ammonium nitrate, and urea) were evaluated for fungal biomass production using a central composite design (CCD) in liquid fermentations. The formulated culture medium (18.72 g/L glucose and 0.39 g/L urea) effectively yielded better fungal biomass production (8 g/L). Based on these results, an extreme vertex design, mixtures with oil palm by-products (PK, hull, and fiber) supplemented with urea, were formulated, finding that PKC stimulated the highest biomass production and laccase enzyme activity in P. ostreatus. The transcriptome of P. ostreatus was obtained, and the chemical composition of the fermented PKC was determined. Transcriptomic analysis revealed the frequency of five key domains with carbohydrate-activated enzyme (CAZy) function: GH3, GH18, CBM1, AA1, and AA5, with activities on lignocellulose. In the fermented PKC, lignin was reduced by 46.9%, and protein was increased by 69.8%. In conclusion, these results show that urea is efficient in the bioconversion of PKC with P. ostreatus as a supplement for ruminants.

The main objective of this study was to determine the influence of the composition of the culture medium and lignocellulosic compounds on the secretion of laccase enzymes by P. ostreatus in submerged cultures. These studies were done using a statistical and systematic approach that allowed the control of the culture media composition. The optimal nutritional conditions were found that simultaneously increased fungal growth and laccase activity in the absence and presence of copper sulfate, a recognized inducer of laccase. Under these conditions, the biochemical aspects of transcripts in P. ostreatus related to laccase secretion were evaluated , which revealed the participation of membrane transporters with high affinity for copper (CTRs) as intermediate candidates for the regulation of three laccase genes, lacc2, lacc6, and lacc10. Moreover, the evaluation of the results of the culture media composition suggests that the regulation of these transporters is closely linked to sufficient nutritional conditions in carbon and nitrogen, with central participation of the metabolism of organic nitrogen in this process. With these findings, it was possible to obtain more profound knowledge of the pretreatment of lignocellulosic biomass by P. ostreatus in a submerged culture that was oriented to determine the role of laccase activity in the biological pretreatment of rice husks.

Agro-industrial lignocellulosic waste can be bioconverted to fungal biomass and then utilized as an alternative feed for ruminants, with potential for ruminal methane (CH₄) mitigation. This study evaluated the changes in the enzymatic expression and nutritional value of palm kernel cake fermented with Pleurotus ostreatus (FPKC), as well as the differences in the in vitro fermentation parameters and methane production in diets based on tropical forages with the inclusion of FPKC and/or tropical forage legumes. The highest activity of laccases and cellulases occurred on day 13 with values of 0.75 ± 0.09 U/g and 266.7 ± 20.8 U/g, respectively. The biological pretreatment decreased (p< 0.05) the contents of neutral detergent fiber (NDF), acid detergent fiber (ADF) and lignin by 29%, 20.5% and 46.6% respectively, while those of crude protein (CP) increased by 69.6%. The inclusion of FPKC and legumes increased (p<0.05) the degradation of DM (DMD), NDF degradability, ADF degradability and CP degradability in the range of 16.9% to 17.3%, 10.9% to 23.8%, 25.7% to 27.5 % and 11.6% to 30.4%, respectively. Production of acetate decreased (p < 0.05) and that of propionate increased (p < 0.05), resulting in a low A:P ratio in the FPKC diets. The total synthesis of CH₄, CH₄/g incubated DM and mL CH₄/g degraded DM decreased (p< 0.05) in the diets with FPKC and legumes between 15% to 24.3%, 15.6% to 24.9% and 27.3% to 35.9%, respectively. In conclusion, the combination of FPKC with legume species in tropical diets for ruminants reduces in vitro methane emissions.