Enzymological Characterization of Atm, the First Laccase from Agrobacterium sp. S5-1, with the Ability to Enhance In Vitro digestibility of Maize Straw

Improvement of aflatoxin B1 degradation ability by Bacillus licheniformis CotA-laccase Q441A mutant

Aflatoxin B1 (AFB1) contamination seriously threatens nutritional safety and common health. Bacterial CotA-laccases have great potential to degrade AFB1 without redox mediators. However, CotA-laccases are limited because of the low catalytic activity as the spore-bound nature. The AFB1 degradation ability of CotA-laccase from Bacillus licheniformis ANSB821 has been reported by a previous study in our laboratory. In this study, a Q441A mutant was constructed to enhance the activity of CotA-laccase to degrade AFB1. After the site-directed mutation, the mutant Q441A showed a 1.73-fold higher catalytic efficiency (kcat/Km) towards AFB1 than the wild-type CotA-laccase did. The degradation rate of AFB1 by Q441A mutant was higher than that by wild-type CotA-laccase in the pH range from 5.0 to 9.0. In addition, the thermostability was improved after mutation. Based on the structure analysis of CotA-laccase, the higher catalytic efficiency of Q441A for AFB1 may be due to the smaller steric hindrance of Ala441 than Gln441. This is the first research to enhance the degradation efficiency of AFB1 by CotA-laccase with site-directed mutagenesis. In summary, the mutant Q441A will be a suitable candidate for highly effective detoxification of AFB1 in the future.

Lignin-Degrading Bacteria in Paper Mill Sludge

The effluents generated in the paper industry, such as black liquor, have a high content of lignin and other toxic components; however, they represent a source of lignin-degrading bacteria with biotechnological potential. Therefore, the present study aimed to isolate and identify lignin-degrading bacteria species in paper mill sludge. A primary isolation was carried out from samples of sludge present in environments around a paper company located in the province of Ascope (Peru). Bacteria selection was made by the degradation of Lignin Kraft as the only carbon source in a solid medium. Finally, the laccase activity (Um-L^-1) of each selected bacteria was determined by oxidation of 2,2'-azinobis-(3-etilbencenotiazolina-6-sulfonate) (ABTS). Bacterial species with laccase activity were identified by molecular biology techniques. Seven species of bacteria with laccase activity and the ability to degrade lignin were identified. The bacteria Agrobacterium tumefasciens (2), Klebsiella grimontii (1), and Beijeinckia fluminensis (1) were reported for first time. K. grimowntii and B. fluminensis presented the highest laccase activity, with values of 0.319 ± 0.005 UmL^-1 and 0.329 ± 0.004 UmL^-1, respectively. In conclusion, paper mill sludge may represent a source of lignin-degrading bacteria with laccase activity, and they could have potential biotechnological applications.

Biological depolymerization of lignin using laccase harvested from the autochthonous fungus Schizophyllum commune employing various production methods and its efficacy in augmenting in vitro digestibility in ruminants

A laccase-producing hyper performer, Schizophyllum commune, a white-rot fungus, was evaluated for its ability to selectively degrade lignin of diverse crop residues in vitro. Relative analysis of crop residue treatment using laccase obtained from immobilized cells demonstrated degradation of 30-40% in finger millet straw and sorghum stover, 27-32% in paddy straw, 21% in wheat straw, and 26% in maize straw, while 20% lignin degradation was observed when purified and recombinant laccase was used. Further investigations into in vitro dry matter digestibility studies gave promising results recording digestibility of 54-59% in finger millet straw 33-36% in paddy straw and wheat straw, 16% in maize straw for laccase obtained from cell immobilization method, whereas 14% digestibility was observed when purified and recombinant laccase was used. Sorghum stover recorded digestibility of 13-15% across all straws treated with laccase. The results obtained elucidated the positive influence of laccase treatment on lignin degradation and in vitro dry matter digestibility. The present research gave encouraging figures confirming the production of laccase using the cell immobilization method to be an efficient production method commensurate with purified and recombinant laccase under conditions of submerged cultivation, proclaiming a cost-effective, environmentally safe green technology for effectual lignin depolymerization.

Draft Genome Sequence of Lignin-Degrading Agrobacterium sp. Strain S2, Isolated from a Decaying Oil Palm Empty Fruit Bunch

We report the draft genome sequence of Agrobacterium sp. strain S2, isolated from a decaying oil palm empty fruit bunch (OPEFB) in Negeri Sembilan, Malaysia, which yields potential genes encoding lignin degradation enzymes. This genome of 9,722,071 bp exhibited 58.9% GC content, 10,416 coding genes, and 12 RNAs.

We report the draft genome sequence of Agrobacterium sp. strain S2, isolated from a decaying oil palm empty fruit bunch (OPEFB) in Negeri Sembilan, Malaysia, which yields potential genes encoding lignin degradation enzymes. This genome of 9,722,071 bp exhibited 58.9% GC content, 10,416 coding genes, and 12 RNAs.

Heterologous Expression of Laccase From Lentinula edodes in Pichia pastoris and Its Application in Degrading Rape Straw

Rape straw cannot be efficiently degraded and utilized by ruminants due to its severe lignification and complex cross-linked structure between fiber and lignin. The laccases can catalyze the inter-unit bond cleavage in lignin substrates. Therefore, this study investigated the recombinant laccase from Lentinula edodes (LeLac) and its application in degrading rape straw. The LeLac was expressed using Pichia pastoris. It had the maximum activity at 60°C and pH 3.0 using ABTS as substrate and at 50°C and pH 4.0 using o-tolidine as substrate. The LeLac exhibited preferential oxidation of ABTS and featured resistance to high temperature, but relatively poor thermal stability. The LeLac activity could be strengthened by Cu²⁺ in dose-dependent manners. The LeLac could tolerate 15% of ethanol and methanol. The optimal pH for the lignin degradation of rape straw acid detergent fiber (ADF) by LeLac was 4.0. The LeLac could improve the cellulose enzymolysis of rape straw ADF by degrading its lignin. Relatively fewer lignin but more soluble phenols from original rape straw were removed by LeLac. The enhancement of enzymatic hydrolysis in original rape straw should be a combined result of polyphenols removal and lignin degradation caused by LeLac. This study demonstrated that the LeLac could improve the utilization of rape straw by degrading its lignin, meanwhile it’s worth noting that removing the soluble phenols by LeLac might also play an important role.

Multiple Tolerance and Dye Decolorization Ability of a Novel Laccase Identified from Staphylococcus Haemolyticus

Laccases are multicopper oxidases with important industrial value. In the study, a novel laccase gene (mco) in a Staphylococcus haemolyticus isolate is identified and heterologously expressed in Escherichia coli. Mco shares less than 40% of amino acid sequence identities with the other characterized laccases, exhibiting the maximal activity at pH 4.0 and 60°C with 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid) diammonium salt (ABTS) as a substrate. Additionally, the Mco is tolerant to a wide range of pH, heavy metal ions and many organic solvents, and it has a high decolorization capability toward textile dyes in the absence of redox mediators. The characteristics of the Mco make this laccase potentially useful for industrial applications such as textile finishing. Based on BLASTN results, mco is found to be widely distributed in both the bacterial genome and bacterial plasmids. Its potential role in oxidative defense ability of staphylococci may contribute to the bacterial colonization and survival.

CotA laccase, a novel aflatoxin oxidase from Bacillus licheniformis, transforms aflatoxin B1 to aflatoxin Q1 and epi-aflatoxin Q1

In the present study, the CotA protein from Bacillus licheniformis ANSB821 was cloned and expressed in Escherichia coli. Apart from the laccase activities, we found that the recombinant CotA could effectively oxidize aflatoxin B1 in the absence of redox mediators. The Km, Kcat and Vmax values of the recombinant CotA towards aflatoxin B1 were 60.62 μM, 0.03 s-1 and 10.08 μg min-1 mg-1, respectively. CotA-mediated aflatoxin B1 degradation products were purified and identified to be aflatoxin Q1 and epi-aflatoxin Q1. The treatment of human liver cells L-02 with aflatoxin Q1 and epi-aflatoxin Q1 did not suppress cell viability and induce apoptosis. Molecular docking simulation revealed that hydrogen bonds and van der Waals interaction played an important role in aflatoxin B1-CotA stability. These findings in the current study are promising for a possible application of CotA as a novel aflatoxin oxidase in degrading AFB1 in food.

Heterologous expression of a Streptomyces cyaneus laccase for biomass modification applications

Laccases are used for the conversion of biomass into fermentable sugars but it is difficult to produce high yields of active laccases in heterologous expression systems. We overcame this challenge by expressing Streptomyces cyaneus CECT 3335 laccase in Escherichia coli (ScLac) and we achieved a yield of up to 104 mg L-1 following purification by one-step affinity chromatography. Stability and activity assays using simple lignin model substrates showed that the purified enzyme preparation was active over a broad pH range and at high temperatures, suggesting it would be suitable for biomass degradation. The reusability of ScLac was also demonstrated by immobilizing the enzyme on agarose beads with a binding yield of 33%, and by the synthesis of cross-linked enzyme aggregates with an initial activity recovery of 72%.