Production of spore laccase from Bacillus pumilus W3 and its application in dye decolorization after immobilization.

Given that spore laccase from the Bacillus genus is heat- and alkali-resistant, it is more suitable for industrial applications than fungal laccase. To determine the optimal culture conditions for spore laccase production, the effects of Cu2+ concentration, oxygen content, and culture time on spore laccase production from Bacillus pumilus W3 were investigated. The optimal production parameters were 0.2 mM of Cu2+, 200 rpm shaking speed, 100 mL liquid loading, and 5 days of cultivation. Spore laccase was efficiently immobilized on amino-functionalized celite. When used in dye decolorization, the immobilized spore laccase removed 84.15% of methyl green and 69.70% of acid red 1 after 48 h of treatment. Moreover, the immobilized spore laccase retained 87.04% of its initial decolorization activity after six cycles in the decolorization of acid red 1. These insights into the culture conditions and immobilization of spore laccases should be useful in the development of spore laccase as a biocatalyst in the treatment of textile wastewater.

Molecular cloning, characterization, and dye-decolorizing ability of a temperature- and pH-stable laccase from Bacillus subtilis X1.

Laccases from fungal origin are typically unstable at high temperatures and alkaline conditions. This characteristic limits their practical applications. In this study, a new bacterial strain exhibiting laccase activity was isolated from raw fennel honey samples and identified as Bacillus subtilis X1. The CotA-laccase gene was cloned from strain X1 and efficiently expressed in Escherichia coli in a biologically active form. The purified recombinant laccase demonstrated an extensive pH range for catalyzing substrates and high stability toward alkaline pH and high temperatures. No loss of laccase activity was observed at pH 9.0 after 10 days of incubation, and approximately 21 % of the initial activity was detected after 10 h at 80 °C. Two anthraquinonic dyes (reactive blue 4 and reactive yellow brown) and two azo dyes (reactive red 11 and reactive brilliant orange) could be partially decolorized by purified laccase in the absence of a mediator. The decolorization process was efficiently promoted when methylsyringate was present, with more than 90 % of color removal occurring in 3 h at pH 7.0 or 9.0. These unusual properties indicated a high potential of the novel CotA-laccase for industrial applications.