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. 2020 Sep 16;7(9):200688.
doi: 10.1098/rsos.200688. eCollection 2020 Sep.

Degradation and detoxification of azo dyes with recombinant ligninolytic enzymes from Aspergillus sp. with secretory overexpression in Pichia pastoris

Siqi Liu  1 , Xiaolin Xu  1 , Yanshun Kang  1 , Yingtian Xiao  1 , Huan Liu  1
Affiliations

Degradation and detoxification of azo dyes with recombinant ligninolytic enzymes from Aspergillus sp. with secretory overexpression in Pichia pastoris

Siqi Liu et al. R Soc Open Sci. .

Abstract

Ligninolytic enzymes, including laccase (Lac), manganese peroxidase (MnP) and lignin peroxidase (LiP), have attracted much attention in the degradation of contaminants. Genes of Lac (1827 bp), MnP (1134 bp) and LiP (1119 bp) were cloned from Aspergillus sp. TS-A, and the recombinant Lac (69 kDa), MnP (45 kDa) and LiP (35 kDa) were secretory expressed in Pichia pastoris GS115, with enzyme activities of 34, 135.12 and 103.13 U l-1, respectively. Dyes of different structures were treated via the recombinant ligninolytic enzymes under the optimal degradation conditions, and the result showed that the decolourization rate of Lac on Congo red (CR) in 5 s was 45.5%. Fourier-transform infrared spectroscopy, gas chromatography-mass spectrometry analysis and toxicity tests further proved that the ligninolytic enzymes could destroy the dyes, both those with one or more azo bonds, and the degradation products were non-toxic. Moreover, the combined ligninolytic enzymes could degrade CR more completely compared with the individual enzyme. Remarkably, besides azo dyes, ligninolytic enzymes could also degrade triphenylmethane and anthracene dyes. This suggests that ligninolytic enzymes from Aspergillus sp. TS-A have the potential for application in the treatment of contaminants.

Keywords: Aspergillus; azo dyes; degradation; detoxification; ligninolytic enzymes.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1.
Figure 1.
Determination of protein and enzyme activities: (a) OD600 of recombinant Pichia pastoris GS115; (b) changes in protein concentration in recombinant yeast fermentation; (c) activities of recombinant enzymes; and (d) SDS-PAGE results of the recombinant enzymes from P. pastoris, where M represents markers, and Lac, LiP and MnP represent the SDS-PAGE results of the recombinant enzymes from GS115-Lac, GS115-LiP and GS115-MnP, respectively.
Figure 2.
Figure 2.
Effects of different temperatures, pH and metal ion concentrations on the activities of recombinant enzymes: (a) effects of different temperatures on recombinant enzymes; (b) effects of different pH on recombinant enzymes; (c) effects of different metal ion concentrations on the activities of Lac; (d) effects of different metal ion concentrations on the activities of MnP; and (e) effects of different metal ion concentrations on the activities of LiP.
Figure 3.
Figure 3.
Recombinant enzymes degradation of different dyes.
Figure 4.
Figure 4.
FTIR spectra of azo dyes and their degradation products during the degradation by recombinant enzymes: (a) MY1 and degradation products by LiP, Lac and MnP; and (b) CR and degradation products by LiP, Lac and MnP.
Figure 5.
Figure 5.
Possible degradation pathways of azo dyes degraded by MnP, LiP and Lac, as obtained through GC-MS analysis. (a) Possible degradation pathways of MY1 by MnP, LiP and Lac; and (b) possible degradation pathways of Congo red by MnP, LiP, Lac and combined; combined: LiP + MnP + Lac.
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