Copper Induction of Laccase Isoenzymes in the Ligninolytic Fungus Pleurotus ostreatus

Abstract

Pleurotus ostreatus is a white rot basidiomycete that produces several extracellular laccase isoenzymes, including phenol oxidase A1b (POXA1b), POXA2, and POXC. POXC was the most abundant isoenzyme produced under all of the growth conditions examined in this study. Copper was the most efficient inducer of laccase activity among the putative inducers tested. The amounts of all of the previously described laccase isoenzymes increased substantially in copper-supplemented cultures. Under these conditions expression of POX isoenzymes was regulated at the level of gene transcription. It is worth noting that poxa1b mRNA was the most abundant induced transcript at all of the growth times analyzed, and the amount of this mRNA increased until day 7. The discrepancy between the poxa1b transcript and protein amounts can be explained by the presence of a high level of the protein in P. ostreatus cellular extract, which indicated that the POXA1b isoenzyme could be inefficiently secreted and/or that its physiological activity could occur inside the cell or on the cell wall. Moreover, the POXA1b isoenzyme behaved uniquely, as its activity was maximal on the second day of growth and then decreased. An analysis performed with protease inhibitors revealed that the loss of extracellular POXA1b activity could have been due to the presence of specific proteases secreted into the copper-containing culture medium that affected the extracellular POXA1b isoenzyme.

Screening of inducers for laccase production by Lentinula edodes in liquid medium

“…1B). Copper is a laccase cofactor which presents four cupric ions each associated with one single polypeptide chain (23) but it also has been proved that this element may play an important role in laccase genes regulation at transcription level as showed in Trametes versicolor (7) Phanerochaete chrysosporium (9), Pleurotus ostreatus (18) and Coriolopsis rigida (20). The 250 µM Cu provided the highest laccase activity in LN cultures, which is in accordance to the findings for other fungi, like T. versicolor (400 µM) (7), P. ostreatus (1.0 mM) (3) and V. volvacea (200 µM) (6).…”

Heterologous expression of laccase cDNA from Ceriporiopsis subvermispora yields copper-activated apoprotein and complex isoform patterns

“…Previous investigations have stressed the importance of copper in the regulation of laccase at the transcriptional level Soden & Dobson, 2001;Palmieri et al, 2000;Galhaup et al, 2002). We previously demonstrated that under low-copper conditions, lcs-1 is not efficiently transcribed in C. subvermispora .…”

“…Laccase isoenzyme multiplicity is a phenomenon observed in several fungi, and in the case of Pleurotus sajor-caju (Soden & Dobson, 2001), the basidiomycete CECT 20197 (Mansur et al, 1997), Pleurotus ostreatus (Palmieri et al, 2000), Trametes villosa , Agaricus bisporus (Perry et al, 1993) and Rhizoctonia solani (Wahleithmer et al, 1995), families of structurally related genes have been described. In the case of C. subvermispora, over four isoforms are observed, with different substrate specificity, but only one gene, lcs-1, has been identified Salas et al, 1995).…”

Assessing the tolerance of immobilized laccase from a salt-tolerant strain of Trichoderma viride Pers NFCCI-2745 to heavy metal ions, detergents and copper chelating agents

“…Laccase is a copper-dependent enzyme, and the enzyme immobilized in copper alginate is likely to retain more activity than laccase immobilized using other methods. Laccase of Pleurotus ostreatus and Ganoderma sp were successfully entrapped in copper alginate beads and decolorized some synthetic dyes efficiently (Palmieri et al 2000;Teerapatsakul et al 2008). The biotreatment of industrial effluents that contain heavy metals, detergents, copper chelating agents and phenolic compounds arises a great concern to industries as these compounds are either toxic to microbes or they act as non-competitive inhibitors or as denaturing agents for several enzymes.…”