Spore cells from BPA degrading bacteria Bacillus sp. GZB displaying high laccase activity and stability for BPA degradation

Abstract

Laccase has been applied extensively as a biocatalyst to remove different organic pollutants. This study characterized a spore-laccase from the bisphenol A (BPA)-degrading strain Bacillus sp. GZB. The spore-laccase was encoded with 513 amino acids, containing spore coat protein A (CotA). It showed optimal activity at 70 °C and pH = 7.2 in presence of 2, 6-dimethoxyphenol. At 60 °C, optimal activity was also seen at pH = 3.0 and pH = 6.8 with 2, 2′-azino-bis (3-ethylbenzothiazoline-6-sulfonate) and syringaldazine, respectively. The spore-laccase was stable at high temperature, at acidic to alkaline pH values, and in the presence of different organic solvents. Spore-laccase activity was increased by introducing Cu2+, Mg2+, and Na+, but was strongly inhibited by Fe2+, Ag+, l-cysteine, dithiothreitol, and NaN3. The cotA gene was cloned and expressed in E. coli BL21 (DE3); the purified protein was estimated as having a molecular weight of ~63 kDa. Different synthetic dyes and BPA were effectively decolorized or degraded both by the spore laccase and recombinant laccase. When BPA oxidation was catalyzed using laccase, there was an initial formation of phenoxy radicals and further oxidation or CC bond cleavage of the radicals produced different organic acids. Detailed reaction pathways were developed based on nine identified intermediates. The acute toxicity decreased gradually during BPA degradation by laccase. This study is the first report about a genus of Bacillus that can produce a highly active and stable laccase to degrade BPA.