Abstract
Laccases are a class of multi-copper oxidases with important industrial values. A thermotolerant laccase produced by a basidiomycete fungal strain Cerrena unicolor CGMCC 5.1011 was studied. With glycerin and peptone as the carbon and nitrogen sources, respectively, a maximal laccase activity of 121.7 U/mL was attained after cultivation in the shaking flask for 15 days. Transcriptomics analysis revealed an expressed laccase gene family of 12 members in C. unicolor strain CGMCC 5.1011, and the gene and cDNA sequences were cloned. A glycosylated laccase was purified from the fermentation broth of Cerrena unicolor CGMCC 5.1011 and corresponded to Lac2 based on MALDI-TOF MS/MS identification. Lac2 was stable at pH 5.0 and above, and was resistant to organic solvents. Lac2 displayed remarkable thermostability, with half-life time of 1.67 h at 70 ºC. Consistently, Lac2 was able to completely decolorize malachite green (MG) at high temperatures, whereas Lac7 from Cerrena sp. HYB07 resulted in accumulation of colored MG transformation intermediates. Molecular dynamics simulation of Lac2 was conducted, and possible mechanisms underlying Lac2 thermostability were discussed. The robustness of C. unicolor CGMCC 5.1011 laccase would not only be useful for industrial applications, but also provide a template for future work to develop thermostable laccases.
Highlights
Laccases (EC 1.10.3.2) are copper-containing oxidases catalyzing oxidation of phenolic/non-phenolic ligninrelated compounds and recalcitrant environmental pollutants (Baldrian 2006; Couto and Herrera 2006)
Laccase production by C. unicolor CGMCC 5.1011 C. unicolor strain CGMCC 5.1011 was verified by 18 s rDNA sequencing
Glycerin was the best carbon source for strain CGMCC 5.1011, and it allowed for significant accumulation of laccase by Cerrena maxima, Fomes fomentarius and Pseudotrametes gibbosa
Summary
Laccases (EC 1.10.3.2) are copper-containing oxidases catalyzing oxidation of phenolic/non-phenolic ligninrelated compounds and recalcitrant environmental pollutants (Baldrian 2006; Couto and Herrera 2006). Because laccases have low substrate specificity, utilize oxygen as final electron acceptor and produce water as only by-product, they find applications in paper pulping and bleaching, textile refining, dye decolorization, bioremediation, organic synthesis, juice and wine clarification, etc. (Ai et al 2015; Yang et al 2017a) laccase applications are hampered by low production yields and reduced performance under industrial conditions such as high temperatures (Yang et al 2017a). We continued our quest for laccase-secreting Cerrena and investigated a C. unicolor strain CGMCC 5.1011. The research presented provided a novel laccase with thermotolerance and thermostability that would be desirable for industrial applications
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