Independent behavior of bacterial laccases to inducers and metal ions during production and activity

Abstract

Laccase, a blue copper oxidase, is an enzyme that is involved in the oxidation of aromatic compounds which prove otherwise difficult to degrade in the environment. The substrates of laccase are xenobiotics and synthetic dyes. The isolation of bacterial strains was investigated for laccase production and its activity. The medium for production was a high nitrogen medium containing aromatic compounds as inducers, for instance, guaiacol, phenol red and black liquor (from pulp and paper industry) gave higher production. The enzymes of isolated bacteria had the optimum pH and temperature in the range of 3 to 5 and 32 to 37°C, respectively. Furthermore, metal ions had an effect on the laccase enzyme; MnSO₄ and CuSO₄ showed a significant increase in laccase activity. However, the effects of metal ions on either laccase production or laccase activity were not clear. The laccase production and activity were dependent on species of bacterial strains. The laccase bacteria were identified as Rhodococcus sp., Enterobacter sp., Staphylococcus saprophyticus and Delftia tsuruhatensis. The synthetic dyes were determined in the reduction of color using the G32 strain; this strain gave 20 to 65% of dye reduction within three days.

Key words: Bacterial laccases, 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid (ABTS), inducers, metal ions, dye reduction.