An extracellular thermo-alkali-stable laccase from Bacillus tequilensis SN4, with a potential to biobleach softwood pulp

Degradation of residual lignin in kraft pulp by chemical bleaching is implicated in causing environmental pollution. The use of thermo- and alkali-tolerant bacterial laccases is considered to be important biological alternative to chemical processing. Laccases from Bacillus species have shown promis...

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Bibliographic Details
Published in:3 Biotech 2015-04, Vol.5 (2), p.175-185
Main Authors: Sondhi, Sonica, Sharma, Prince, George, Nancy, Chauhan, Prakram Singh, Puri, Neena, Gupta, Naveen
Format: Article
Language:English
Subjects:
Agriculture
Bacillus
Bacteria
Bioinformatics
Biomaterials
Biotechnology
Cancer Research
Chemistry
Chemistry and Materials Science
Enzymes
High temperature
Original
Original Article
Oxidation
Phenols
Stem Cells
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Summary:Degradation of residual lignin in kraft pulp by chemical bleaching is implicated in causing environmental pollution. The use of thermo- and alkali-tolerant bacterial laccases is considered to be important biological alternative to chemical processing. Laccases from Bacillus species have shown promise in this respect but their intracellular/spore bound presence make their industrial application economically unfeasible. We report here on a novel extracellular active thermo-alkali-stable laccase (SN4 laccase)  which is active at 90 °C and pH 8.0 using 2,6-dimethoxyphenol as substrate from Bacillus tequilensis SN4. SN4 laccase retained 27 % activity for 5 min at 100 °C and more than 80 % activity for 24 h at 70 °C. The enzyme is also stable at a higher pH (9.0–10.0). Enzyme production was optimized by submerged fermentation. Relatively high yields (18,356 nkats ml −1 ) of SN4 laccase was obtained in a medium containing 650 μM MnSO 4 , 350 μM FeSO 4 , and 3.5 % ethanol. A 764-fold increase in laccase activity was observed under optimal conditions. In addition, reduction in kappa number and increase in brightness of softwood pulp by 28 and 7.6 %, respectively, were observed after treatment with SN4 laccase without a mediator. When N -hydroxybenzotriazole was used as a mediator, the kappa number was decreased to 47 % and brightness was increased to 12 %.
ISSN:2190-572X
2190-5738
DOI:10.1007/s13205-014-0207-z