Hyperstabilization of a thermophile bacterial laccase and its application for industrial dyes degradation

Abstract

In the present study, a novel extracellular laccase isolated from Geobacillus stearothermophilus ATCC 10149 was entrapped in a bionanocomposite matrix consisting of copper alginate (Cu-alginate) supplemented with the nanoclay bentonite. After optimization, this nanobiocatalyst was able to degrade up to 90% of Remazol Brilliant Blue R (RBBR) without the addition of redox mediators and retained 70% of its initial activity for at least 1440 h, equivalent to more than 288 uses. The incorporation of nanoclay allowed alginate beads to be used in alkaline pH and strengthened its mechanical properties. Besides, this thermophilic laccase was able to decolorize other structurally different synthetic dyes such as Methyl Orange, Malachite Green and Indigo Carmine. These preliminary results suggested that the nanobiocatalyst could be a suitable option for dye decolorization and be further developed for large scale bioremediation of toxic dyes.

Keywords: Bentonite; Biodegradation; Cu-alginate; Geobacillus; Immobilization; Nanoclay.

Fig. 1

Geobacillus growth curve (filled square) and RBBR decolorization (grey bars). Optical Density (OD) was measured at 600 nm in a Shimadzu 1603 spectrophotometer; dye decolorization was followed with a ELx800 plate reader at 595 nm

Fig. 2

Schematic representation of nanobiocatalyst production. The laccase secreted during G. stearothermophilus growth was concentrated and purified. Then, the laccase solution was mixed with alginate and bentonite and entrapped by ionotropic gelation in 0.1 M CuSO₄. The obtained beads were used for RBBR decolorization in a bioreactor

Fig. 3

Relative laccase activity at different pH of free (open circle) and immobilized laccase (filled square). Activity was evaluated by RBBR decolorization at 5 h

Fig. 4

Operational stability of the Cu-alginate biocatalyst (filled square) and the bentonite-nanobiocatalyst (open circle). Each use was evaluated by RBBR decolorization at 5 h and 25 °C