Effect of Cu<sup>2+</sup>, Mn<sup>2+</sup> and aromatic compounds on the production of laccase isoforms by <i>Coprinus comatus</i>

Abstract

Six different extracellular laccase isoforms were identified in submerged cultures of the commercially important edible mushroom, Coprinus comatus. Although laccase activity (~55IU/L) was readily detectable in unsupplemented control cultures containing 1.6μM Cu2+ after 22-day incubation, mean enzyme levels (~150–185IU/L) were 2.7–3.4-fold higher in cultures supplemented with 0.5–3.0mM Cu2+. Laccase production was also stimulated by Mn supplementation over the range 0.05–0.8mM Mn2+, and the peak value of ~225IU/L recorded after 22 days in cultures containing 0.8mM added Mn2+ was 4.5-fold higher compared with unsupplemented controls. Of 12 aromatic compounds tested for their effect on laccase isozyme production by C. comatus, highest laccase levels ~188IU/L), equivalent to a 4.4-fold increase compared with unsupplemented controls (~43IU/L), were recorded after 22 days in cultures supplemented with 3.0mM caffeic acid. Other aromatic compounds tested all stimulated laccase production, with peak enzyme levels 1.3–3.3-fold higher compared with unsupplemented controls. Extracellular laccase levels in cultures supplemented with optimal concentrations of Mn2+ and caffeic acid together were 38% and 15% lower, respectively, compared with cultures containing the separate supplements. Lac1 was the most abundant laccase isoform produced under all the conditions tested, but marked differences were observed in the production patterns of Lac2–Lac6.