Decolorization of synthetic dyes by immobilized spore from Bacillus amyloliquefaciens

Isolation of Bacillus sp. with high laccase activity for green biodecolorization of synthetic textile dyes

New Bacillus sp. strains with spore-laccase activity were isolated from rotten wood and soil samples and were identified as Bacillus sp. FM-78 and Bacillus paramycoides FM-86 by 16S rDNA gene sequence analysis. Both laccases were stable at broad pH range and high temperature. The laccase of strain FM-78 showed preferable activity and stability, with no loss of activity after 7 days incubation at pH 9.0, and 20.36% of its initial activity obtained after 10 h at 80 °C. 1 mmol/L EDTA, NaN₃ and SDS resulted in about 46-59% inactivation and strongly inhibition (87.88%) was caused by 1 mmol/L L-cysteine. However, the spore laccase could tolerate towards 0.5 mol/L NaCl as well as 10% of organic solvents. Reactive black 5, reactive blue 19 and crystal violet were decolorized by the spore laccase in the absence of mediator. The decolorization process was efficiently promoted with the presence of acetosyringone, and the color removal ratio was more than 80% in 1 h with the pH values of 6.6 or 9.0. Finally, the above unusual properties of Bacillus sp. spore laccase indicated it as a potential candidate in the dye decolorization in an ecofriendly and cost-effective way.

Biochemical and Structural Properties of a High-Temperature-Active Laccase from Bacillus pumilus and Its Application in the Decolorization of Food Dyes

A novel laccase gene isolated from Bacillus pumilus TCCC 11568 was expressed, and the recombinant laccase (rLAC) displayed maximal activity at 80 °C and at pH 6.0 against ABTS. rLAC maintained its structural integrity at a high temperature (355 K) compared to its tertiary structure at a low temperature (325 K), except for some minor adjustments of certain loops. However, those adjustments were presumed to be responsible for the formation of a more open access aisle that facilitated the binding of ABTS in the active site, resulting in a shorter distance between the catalytic residue and the elevated binding energy. Additionally, rLAC showed good thermostability (≤70 °C) and pH stability over a wide range (3.0–10.0), and displayed high efficiency in decolorizing azo dyes that are applicable to the food industry. This work will improve our knowledge on the relationship of structure–function for thermophilic laccase, and provide a candidate for dye effluent treatment in the food industry.

Draft Genome Sequence and Annotation of the Synthetic Textile Dye-Decolorizing Strain Bacillus amyloliquefaciens AD20, Isolated from a Dye Waste Pond

A limited number of Bacillus amyloliquefaciens genome sequences have been generated and are available in the public domain from soil, fermented foods, and plants. Here, we report the whole-genome sequence of B. amyloliquefaciens AD20, isolated from a dye pond with azo dye decolorization capabilities.

Co-immobilized spore laccase/TiO2 nanoparticles in the alginate beads enhance dye removal by two-step decolorization

Combinatorial application of different dye removal methods with specific features can lead to a novel and robust decolorizing system. In this study the bacterial spore laccase and TiO₂ nanoparticles were co-entrapped to enhance dye degradation. The optimum entrapment conditions were achieved in the presence of alginate 2% (w/v) and Ca²⁺ (0.2M), Cu²⁺ (0.05M) and Zn²⁺ (0.25M) as matric polymer and counterions, respectively. Immobilized laccase showed a wide range of pH and temperature stability in comparison to the free spores. The entrapped degradation systems include single laccase, single TiO₂, laccase + TiO₂ (one-step remediation), TiO₂/laccase (two-step remediation), and laccase/TiO₂ (two-step remediation) that result to the 22%, 26% 45.6%, 47.6%, and 69.3% indigo carmine decolorization in 60 min. In the kinetic studies, the half-life of indigo carmine (25 mg/l) in the remediation processes containing laccase, TiO₂, laccase + TiO₂, TiO₂/laccase, and laccase/TiO₂ was calculated as 173, 138, 161, 115, and 57 min, respectively. The degradation products by co-entrapped system were not toxic against Sorghum vulgare. The results showed two-step decolorization by co-entrapped spore laccase and TiO₂ nanoparticles, including the pretreatment of dye by laccase, and then, treatment by TiO₂ has potential for degradation of indigo carmine.

Enzymatic characterization, molecular dynamics simulation, and application of a novel Bacillus licheniformis laccase

A new laccase gene from newly isolated Bacillus licheniformis TCCC 111219 was actively expressed in Escherichia coli. This recombinant laccase (rLAC) exhibited a high stability towards a wide pH range and high temperatures. 170% of the initial activity was detected at pH 10.0 after 10-d incubation, and 60% of the initial activity was even kept after 2-h incubation at 70 °C. It indicated that only single type of extreme environment, such as strong alkaline environment (300 K, pH 12) or high temperature (370 K, pH 7), did not show obvious impact on the structural stability of rLAC during molecular dynamics simulation process. But the four loop regions of rLAC where the active site is situated were seriously destroyed when strong alkaline and high temperature environment existed simultaneously (370 K, pH 12) because of the damage of hydrogen bonds and salt bridges. Moreover, this thermo- and alkaline-stable enzyme could efficiently decolorize the structurally differing azo, triphenylmethane, and anthraquinone dyes with appropriate mediator at pH 3.0, 7.0, and 9.0 at 60 °C. These rare characteristics suggested its high potential in industrial applications to decolorize textile dyeing effluent.

Current Development in Decolorization of Synthetic Dyes by Immobilized Laccases

The world today is in a quest for new means of environmental remediation as the methods currently used are not sufficient to halt the damage. Mostly, a global direction is headed toward a shift from traditional chemical-based methods to a more ecofriendly alternative. In this context, biocatalysis is seen as a cost-effective, energy saving, and clean alternative. It is meant to catalyze degradation of recalcitrant chemicals in an easy, rapid, green, and sustainable manner. One already established application of biocatalysis is the removal of dyes from natural water bodies using enzymes, notably oxidoreductases like laccases, due to their wide range of substrate specificity. In order to boost their catalytic activity, various methods of enhancements have been pursued including immobilization of the enzyme on different support materials. Aside from increased catalysis, immobilized laccases have the advantages of higher stability, better durability against harsh environment conditions, longer half-lives, resistance against protease enzymes, and the ability to be recovered for reuse. This review briefly outlines the current methods used for detoxification and decolorization of dye effluents stressing on the importance of laccases as a revolutionary biocatalytic solution to this environmental problem. This work highlights the significance of laccase immobilization and also points out some of the challenges and opportunities of this technology.

Simultaneous hydrogen production and decolorization of denim textile wastewater: kinetics of decolorizing of indigo dye by bacterial and fungal strains

This study proposes the treatment and valorization of denim textile effluents through a fermentative hydrogen production process. Also, the study presents the decolorizing capabilities of bacterial and fungal isolates obtained from the fermented textile effluents. The maximum hydrogen production rate was 0.23 L H₂/L-d, achieving at the same time color removal. A total of thirty-five bacteria and one fungal isolate were obtained from the fermented effluents and screened for their abilities to decolorize indigo dye, used as a model molecule. From them, isolates identified as Bacillus BT5, Bacillus BT9, Lactobacillus BT20, Lysinibacillus BT32, and Aspergillus H1T showed notable decolorizing capacities. Lactobacillus BT20 reached 90% of decolorization using glucose as co-substrate after 11 days of incubation producing colorless metabolites. Bacillus BT9 was able to utilize the indigo dye as the sole carbon source achieving a maximum decolorization of 60% after 9 days of incubation and producing a red-colored metabolite. In contrast, Bacillus BT5 and Lysinibacillus BT32 exhibited the lowest percentages of decolorization, barely 33% after 16 and 11 days of incubation, respectively. When Aspergillus H1T was grown in indigo dye supplemented with glucose, 96% of decolorization was reached after 2 days. This study demonstrates the valorization of denim textile effluents for the production of hydrogen via dark fermentation with concomitant color removal.

The heterologous expression, characterization, and application of a novel laccase from Bacillus velezensis

Laccases have a huge potential in numerous environmental and industrial applications due to the ability to oxidized a wide range of substrates. Here, a novel laccase gene from the identified Bacillus velezensis TCCC 111904 was heterologously expressed in Escherichia coli. The optimal temperature and pH for oxidation by recombinant laccase (rLac) were 80 °C and 5.5, respectively, in the case of the substrate 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), and 80 °C and 7.0, respectively, in the case of 2,6-dimethoxyphenol (2,6-DMP). rLac exhibited high thermostability and pH stability over a wide range (pH 3.0, 7.0, and 9.0). Additionally, most of the metal ions did not inhibit the activity of rLac significantly. rLac showed great tolerance against high concentration of NaCl, and 50.8% of its initial activity remained in the reaction system containing 500 mM NaCl compared to the control. Moreover, rLac showed a high efficiency in decolorizing different types of dyes including azo, anthraquinonic, and triphenylmethane dyes at a high temperature (60 °C) and over an extensive pH range (pH 5.5, 7.0, and 9.0). These unique characteristics of rLac indicated that it could be a potential candidate for applications in treatment of dye effluents and other industrial processes.

Decolorization of dyes by a novel sodium azide-resistant spore laccase from a halotolerant bacterium, Bacillus safensis sp. strain S31

The aim of this work was to find a new stable laccase against inhibitors and study the decolorization ability of free and immobilized laccase on different classes of dyes. Spores from a halotolerant bacterium, Bacillus safensis sp. strain S31, isolated from soil samples from a chromite mine in Iran showed laccase activity with maximum activity at 30 °C and pH 5.0 using 2, 2-azino-bis (3-ethylbenzothiazoline-6-sulfonate) (ABTS) as the substrate. The enzyme retained about 60% of its initial activity in the presence of 10% (v v^-1) methanol, ethanol, and acetone. In contrast to many other laccases, NaN₃, at 0.1 and 1 mM concentrations, showed a slight inhibitory effect on the enzyme activity. Also, the spore laccase (8 U l^-1) decolorized malachite green, toluidine blue, and reactive black 5 at acidic pH values; the highest decolorization percent was 75% against reactive black 5. It was observed that addition of ABTS as a redox mediator enhanced the decolorization activity. Furthermore, immobilized spore laccase encased in calcium alginate beads decolorized 95% of reactive black 5 in the absence of mediators. Overall, this isolated spore laccase might be a potent enzyme to decolorize dyes in polluted wastewaters, especially those containing metals, salts, solvents, and sodium azide.

Production of spore laccase from Bacillus pumilus W3 and its application in dye decolorization after immobilization

Given that spore laccase from the Bacillus genus is heat- and alkali-resistant, it is more suitable for industrial applications than fungal laccase. To determine the optimal culture conditions for spore laccase production, the effects of Cu²⁺ concentration, oxygen content, and culture time on spore laccase production from Bacillus pumilus W3 were investigated. The optimal production parameters were 0.2 mM of Cu²⁺, 200 rpm shaking speed, 100 mL liquid loading, and 5 days of cultivation. Spore laccase was efficiently immobilized on amino-functionalized celite. When used in dye decolorization, the immobilized spore laccase removed 84.15% of methyl green and 69.70% of acid red 1 after 48 h of treatment. Moreover, the immobilized spore laccase retained 87.04% of its initial decolorization activity after six cycles in the decolorization of acid red 1. These insights into the culture conditions and immobilization of spore laccases should be useful in the development of spore laccase as a biocatalyst in the treatment of textile wastewater.

A novel non-blue laccase from Bacillus amyloliquefaciens: secretory expression and characterization

Laccases are copper-containing enzymes which possess a promising potential in many industrial and environmental applications. Here we describe the cloning, extracellular expression and characterization of a novel non-blue laccase from Bacillus amyloliquefaciens in Pichia pastoris. The recombinant enzyme was secreted into the culture supernatant with high activity. It lacks the absorption band at 610 nm typical for blue laccases. However, electron paramagnetic resonance (EPR) spectrum proved the existence of type 1 copper center that was not detectable in the UV-visible spectrum. Metal content analysis revealed that the enzyme contains two copper ions, one iron ion and one zinc ion per protein molecular, suggesting that it is a novel non-blue laccase. The pH and temperature optima of the recombinant laccase were 6.6 and 60°C, respectively, and it was stable at pH 9.0 for 10 days. The enzyme activity was slightly activated by NaCl with concentration up to 200 mM. The purified laccase showed high efficiency in decolorizing reactive black 5 and indigo carmine, achieving more than 93% decolorization after 1h. The extreme robustness of the recombinant B. amyloliquefaciens laccase offers several advantages over most fungal laccases in various industrial applications.