Effect of Nutritional Factors and Copper on the Regulation of Laccase Enzyme Production in Pleurotus ostreatus.

Dinary Durán-Sequeda,Rocío Sierra,Lucía Ramírez,Antonio G Pisabarro,Estibenson Maestre,Manuel Alfaro,Gumer Perez,Daniela Suspes

doi:10.3390/jof8010007

Dinary Durán-Sequeda, Rocío Sierra + Show 6 more

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https://doi.org/10.3390/jof8010007

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Abstract

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.

Highlights

Fungal laccases are glycosylated, multi-copper oxidases that catalyze the oxidation of hydroxyl functional groups on various substrates and the molecular oxygen reduction to water [1,2,3]
Higher biomass production and laccase activity were obtained in cultures with Yeast extract (YE) as the nitrogen source, whereas the highest final glucose concentration, lower biomass, and laccase activities lower than
This study describes a systematic analysis of the composition of the culture medium based on two nutritional factors: glucose as a carbon source and ammonium sulfate or yeast extract as nitrogen sources

Summary

Introduction

Multi-copper oxidases that catalyze the oxidation of hydroxyl functional groups on various substrates and the molecular oxygen reduction to water [1,2,3]. As laccases can oxidize phenolic and non-phenolic compounds, they are attractive in many biotechnological processes such as bioremediation, wastewater treatment, nanobiotechnology, biofuel production, pharmaceuticals, and the food industry [4,5]. Pleurotus ostreatus is a white-rot fungus biotechnological model for studying and producing fungal laccases [6]. This fungus is cultivable on several synthetic or natural media [7], its genome has been decoded [8], and it contains a laccase multi-gene family [9]. Laccase production in P. ostreatus cultures is affected by complex and not fully understood gene expression regulatory mechanisms at multiple levels. Twelve laccase genes have been identified in P. ostreatus monokaryotic (mk) strains, mkPC15 and mkPC9 [10] distributed across several chromosomes: seven on chromosome

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