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

Abstract

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 MnSO4, 350 μM FeSO4, 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 %.

Production of Extracellular Laccase fromBacillus subtilisMTCC 2414 Using Agroresidues as a Potential Substrate

“…Moreover, previous studies have shown maximum laccase activity between 40 and 60°C [38, 39]. The pH profile showed higher laccase activity at 9.0 (266 ± 4.02 U/mL) which is in accordance with Sonica et al [37]. Kuddus et al [26] reported that P. putida laccase exhibited maximum activity at pH 9 (34.45 U/mL) which is also in accordance with the present study results.…”

“…The maximum enzyme activity was observed at 70°C (260.3 ± 6.15 U/mL) using rice bran as a substrate which was well supported by Sonica et al [37] where they have reported comparable activity at 70°C by B. tequilensis using softwood pulp as a substrate. Moreover, previous studies have shown maximum laccase activity between 40 and 60°C [38, 39].…”

Bacterial Laccase Mediated Inhibition of Enzymatic Browning in Apple Juice and Its Sensory Evaluation

“…It was found that laccase fractions were eluted with 1.0 M NaCl gradient which further purified laccase with 48. 49 Bozoglu et al, 2013;Kaira et al, 2015;Muthukumarasamy et al, 2015;Sondhi et al, 2015).…”

Pilot scale production of extracellular thermo‐alkali stable laccase from Pseudomonas sp. S2 using agro waste and its application in organophosphorous pesticides degradation

“…Response surface methodology (RSM) was helpful in enhancement of laccase production several‐fold by critical analysis of each factor, e.g. in the case of B. tequilensis SN4 laccase activity increased about 764‐fold more in comparison with the control in simple medium . Similarly under optimized conditions the activity of laccase from γ‐ Proteobacterium JB gave 9.3‐fold increase over the control…”

“…To date, only a few bacterial laccases, especially Bacillus species such as Bacillus safensis DSKK5, B. tequilensis SN4, Bacillus sp. ADR, B. sphaericus and Bacillus (HR03), Bacillus sp.…”