Production of ligninolytic enzymes by litter-decomposing fungi and their ability to decolorize synthetic dyes

Under explored roles of microbial ligninolytic enzymes in aerobic polychlorinated biphenyl transformation

Polychlorinated biphenyls (PCBs) are persistent organic pollutants in the environment that are responsible for many adverse health effects. Bioremediation appears to be a healthy and cost-effective alternative for remediating PCB-contaminated environments. While some microbial species have been observed to be capable of transforming PCBs, only two different microbial pathways (rdh and bph pathways) have been described to be involved in PCB transformations. Ligninolytic enzymes have been observed or are under suspicion in some microbial PCB transformations. However, the role of these promising PCB-transforming enzymes, which are produced by fungi and some aerobic bacteria, is still unclear. The present review describes their role by identifying microbial PCB-transforming species and their reported ligninolytic enzymes whether proven or suspected to be involved in PCB transformations. There are several lines of evidence that ligninolytic enzymes are responsible for PCB transformations such as (1) the ability of purified laccases from Myceliophthora thermophila, Pycnoporus cinnabarinus, Trametes versicolor, Cladosporium sp, and Coprinus cumatus to transform hydroxy-PCBs; (2) the increased production of laccases and peroxidases by many fungi in the presence of PCBs; and (3) the enhanced PCB transformation by Pseudomonas stutzeri and Sinorhizobium meliloti NM after the addition of ligninolytic enzyme enhancers. However, if the involvement of ligninolytic enzymes in PCB transformation is clearly demonstrated in some fungal species, it does not seem to be implicated in all microbial species suggesting other still unknown metabolic pathways involved in PCB transformation and different from the bph and rdh pathways. Therefore, PCB transformation may involve several metabolic pathways, some involving ligninolytic enzymes, bph or rdh genes, and some still unknown, depending on the microbial species. In addition, current knowledge does not fully clarify the role of ligninolytic enzymes in PCB oxidation and dechlorination. Therefore, further studies focusing on purified ligninolytic enzymes are needed to clearly elucidate their role in PCB transformation.

Eco-friendly TEMPO/laccase/O2 biocatalytic system for degradation of Indigo Carmine: operative conditions and laccase inactivation

The biocatalytic system laccase/TEMPO/O₂ has attracted the attention of researchers over the past two decades. A variety of applications for the system include organic synthesis, modification of cellulose, and oxidative degradation of environmental contaminants. A rigorous and predictable quantitative assessment of the change in enzymatic activity under the influence of a mediator is important for such a system. In this study, the operative conditions for carrying out a model reaction for the degradation of the synthetic dye Indigo Carmine in the presence of Trametes versicolor laccase/TEMPO were determined and the enzyme inactivation under the action of a mediator and substrate was studied. The long-term stability of Trametes versicolor laccase was assessed and the regression model of the response surface of laccase activity under the influence of TEMPO was created. It has been shown that laccase is inactivated in the presence of TEMPO, but the addition of the dye, CuSO₄ or CuCl₂ reduces this effect. The system under study can be used repeatedly for the Indigo Carmine decolorization, however, a gradual falling rate during the process is observed from cycle to cycle. This is due to two reasons - firstly, a decrease in the enzyme activity with each batch and secondly, the consumption of the mediator (22% within 5 days). Relatively high enzyme activity (>40%) is maintained after 73 cycles (1 portion of IC contained 25 μM) using 500 μM TEMPO and 0.12 U mL^-1 laccase. The laccase/TEMPO system has shown its effectiveness in the treatment of artificial wastewater containing high concentrations of Indigo carmine (0.5 g L^-1). In this case, the dye solution becomes 100% colorless within 5 hours in the presence of dye bath components and within 7.5 hours in a buffer solution.

Removal of antibiotics from wastewaters by membrane technology: Limitations, successes, and future improvements

Antibiotics and related pharmaceuticals are applied to enhance public health and life quality. A major environmental concern is wastewaters from pharmaceutical industries, which contain significant amounts of antibiotics. Pharmaceutical industries apply conventional processes (biological, filtration, coagulation, flocculation, and sedimentation) for wastewater treatment, but these approaches cannot remove antibiotics completely. Moreover, unmetabolized antibiotics released by humans and animals are dangerous for municipal and effluent wastewater. Besides, antibiotic resistance is another challenge in treatment of wastewater for superbugs. This comprehensive study summarizes different techniques for antibiotic removal with an emphasis on membrane technology in individual and hybrid systems such as chemical, physical, biological, and conditional-based strategies. A combination of membrane processes with advanced oxidation processes (AOPs), adsorption, and biological treatments can be the right solution for perfect removal. Furthermore, this review briefly compares different procedures for antibiotic removal, which can be helpful for further studies with their advantages and drawbacks.

Graphene environmental biodegradation: Wood degrading and saprotrophic fungi oxidize few-layer graphene

The environmental biodegradability profile of graphene related materials (GRMs) is important to know in order to predict whether these materials will accumulate in soil or will be transformed by primary decomposers. In this study, few-layer graphene (FLG) was exposed to living and devitalized axenic cultures of two white-rot basidiomycetes (Bjerkandera adusta and Phanerochaete chrysosporium) and one soil saprotrophic ascomycete (Morchella esculenta) with or without lignin, for a period of four months. Over this time, the increase of fungal biomass and presence of H₂O₂ and oxidizing enzymes [laccase/peroxidase and lignin peroxidase (LiP)] in growth media was assessed by gravimetric and spectrophotometric measurements, respectively. Raman spectroscopy and transmission electron microscopy (TEM) were used to compare the structure of FLG before and after incubation. All of the test fungi decreased pH in growth media and released H₂O₂ and laccase/peroxidase, but only basidiomycetes released LiP. Independent of growth media composition all fungi were found to be capable to oxidize FLG to a graphene oxide-like material, including M. esculenta, which released only laccase/peroxidase, i.e. the most common enzymes among primary decomposers. These findings suggest that FLG involuntarily released into terrestrial environments would likely be oxidized by soil microflora.

Effects of Ionic Liquids on Metalloproteins

In the past decade, innovative protein therapies and bio-similar industries have grown rapidly. Additionally, ionic liquids (ILs) have been an area of great interest and rapid development in industrial processes over a similar timeline. Therefore, there is a pressing need to understand the structure and function of proteins in novel environments with ILs. Understanding the short-term and long-term stability of protein molecules in IL formulations will be key to using ILs for protein technologies. Similarly, ILs have been investigated as part of therapeutic delivery systems and implicated in numerous studies in which ILs impact the activity and/or stability of protein molecules. Notably, many of the proteins used in industrial applications are involved in redox chemistry, and thus often contain metal ions or metal-associated cofactors. In this review article, we focus on the current understanding of protein structure-function relationship in the presence of ILs, specifically focusing on the effect of ILs on metal containing proteins.

Ideal Feedstock and Fermentation Process Improvements for the Production of Lignocellulolytic Enzymes

The usage of lignocellulosic biomass in energy production for biofuels and other value-added products can extensively decrease the carbon footprint of current and future energy sectors. However, the infrastructure in the processing of lignocellulosic biomass is not well-established as compared to the fossil fuel industry. One of the bottlenecks is the production of the lignocellulolytic enzymes. These enzymes are produced by different fungal and bacterial species for degradation of the lignocellulosic biomass into its reactive fibers, which can then be converted to biofuel. The selection of an ideal feedstock for the lignocellulolytic enzyme production is one of the most studied aspects of lignocellulolytic enzyme production. Similarly, the fermentation enhancement strategies for different fermentation variables and modes are also the focuses of researchers. The implementation of fermentation enhancement strategies such as optimization of culture parameters (pH, temperature, agitation, incubation time, etc.) and the media nutrient amendment can increase the lignocellulolytic enzyme production significantly. Therefore, this review paper summarized these strategies and feedstock characteristics required for hydrolytic enzyme production with a special focus on the characteristics of an ideal feedstock to be utilized for the production of such enzymes on industrial scales.

Purification and characterisation of new laccase from Trametes polyzona WRF03

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Trametes polyzona WRF03 produced high yield of true laccase.

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Trametes polyzona WRF03 laccase was relatively pH and temperature stable.

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Fe²⁺, sodium azide and sodium cyanide greatly inhibited laccase activity.

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Trametes polyzona WRF03 laccase decolorised many classes of synthetic dyes.

The molecular screening for laccase specific gene sequences in Trametes polyzona WRF03 (TpWRF03) using designed oligonucleotide primers analogous to the conserved sequences on the copper-binding regions of known laccases showed positive amplification with an amplicon size corresponding to 1500 bp. The purified TpWRF03 laccase (TpL) is a monomer with a molecular weight corresponding to 66 kDa. The enzyme had an optimal pH of 4.5 and temperature of 55 °C. TpL was most stable within pH of 5.5–6.5 and at a temperature range of 40–50 °C. Sodium azide, sodium cyanide and Fe²⁺ greatly inhibited the enzyme activity. TpL showed more than 50 % decolourisation efficiency on coomassie brilliant blue (72.35 %) and malachite green (57.84 %) but displayed low decolourisation efficiency towards Azure B (1.78 %) and methylene blue (0.38 %). The results showed that TpWRF03 produces high-yield of true laccase with robust properties for biotechnological applications.

The degradative activity and adaptation potential of the litter-decomposing fungus Stropharia rugosoannulata

The ability of the litter-decomposing basidiomycete Stropharia rugosoannulata DSM 11372 to degrade a wide range of structurally different environmental pollutants such as polycyclic aromatic hydrocarbons (PAHs: phenanthrene, anthracene, fluorene, pyrene, and fluoranthene), synthetic anthraquinone dyes containing condensed aromatic rings, environmentally relevant alkylphenol and oxyethylated alkylphenol representatives, and oil was demonstrated within the present study. 9,10-Anthraquinone, phenanthrene-9,10-quinone, and 9-fluorenone were identified as products of anthracene, phenanthrene, and fluorene degradation, respectively. Fungal degradation was accompanied by the production of the ligninolytic enzymes: laccase and Mn peroxidase, suggesting their involvement in pollutant degradation. Extracellular polysaccharide(s) (EPS) and emulsifying compound(s) were concomitantly produced. EPS composed of mannose, glucose, and galactose was isolated from the cultivation medium, and its effects on catalytic properties of purified laccase from S. rugosoannulata (the dominating ligninolytic enzyme under the applied conditions) were studied. A simultaneous decrease of K_M and V_max values observed for the enzymatic oxidation of non-phenolic (2,2-azino-bis-(3-ethylbenzthiazoline-6-sulphonic acid) diammonium salt; ABTS) and phenolic compounds (2,6-dimethoxyphenol) in presence of EPS suggest an interaction of EPS and laccase resulting in a modulation of the catalytic performance of the enzyme, which has, to the best of our knowledge, not been reported before. In line with such a modulation, the laccase-catalyzed oxidation of natural aromatic compounds (veratryl alcohol, adlerol) and environmental pollutants (the alkylphenol representative nonylphenol, the diphenylmethane derivative bisphenol A, and the PAH representative anthracene) was found to be enhanced in presence of EPS. The relevance of such effects for real environmental processes and their implications remain to be investigated.

Ligninolytic Activity at 0 °C of Fungi on Oak Leaves Under Snow Cover in a Mixed Forest in Japan

Despite the importance of litter decomposition under snow cover in boreal forests and tundra, very little is known regarding the characteristics and functions of litter-decomposing fungi adapted to the cold climate. We investigated the decomposition of oak leaves in a heavy snowfall forest region of Japan. The rate of litter weight loss reached 26.5% during the snow cover period for 7 months and accounted for 64.6% of the annual loss (41.1%). Although no statistically significant lignin loss was detected, decolourization portions of oak leaf litter, which was attributable to the activities of ligninolytic fungi, were observed during snow cover period. This suggests that fungi involved in litter decomposition can produce extracellular enzymes to degrade lignin that remain active at 0 °C. Fungi were isolated from oak leaves collected from the forest floor under the snow layer. One hundred and sixty-six strains were isolated and classified into 33 operational taxonomic units (OTUs) based on culture characteristics and nuclear rDNA internal transcribed spacer (ITS) region sequences. To test the ability to degrade lignin, the production of extracellular phenoloxidases by isolates was quantified at 0 °C. Ten OTUs (9 Ascomycota and 1 Basidiomycota) of fungi exhibited mycelial growth and ligninolytic activity. These results suggested that some litter-decomposing fungi that had the potential to degrade lignin at 0 °C significantly contribute to litter decomposition under snow cover.

Bio-bleaching of Remazol brilliant blue-19 by Stereum ostrea

Efficiency of white-rot fungi-Stereum ostrea (S. ostrea) as a test culture and Phanerochaete chrysosporium (P. chrysosporium) as a reference culture in colour removal from a textile dye, Remazol brilliant blue-19 (RBB-19) in medium was compared in this study. S. ostrea was more efficient than P. chrysosporium in decoloration process. Different parameters pH, temperature, sources of carbon and nitrogen, stationary and shaking conditions were optimized for bleaching of dye by the fungal cultures. Optimal growth conditions for decoloration of dye by both cultures were pH 5.0, temperature 35 °C, glucose and fructose as best carbon source at 1 % level, peptone and urea as best nitrogen source and shaking conditions (150 rpm). Culture broth free of colour (99 % of decoloration) was achieved with S. ostrea as against 70 % decoloration by P. chrysosporium on 6th day of incubation. Adsorption of dye to fungal biomass as reflected by colour coating on biomass and participation of lignolytic enzymes in colour removal appeared to be mechanisms involved in decoloration process. The ability of both fungal cultures in removal of colour in effluents with dyes collected from silk saree-weaving cottage unit was tested. S. ostrea was also found to be more effective in colour removal from effluent. S. ostrea appears to be a promising culture for application of bioremediation in decoloration of dyes.

Production of Extracellular Laccase from Bacillus subtilis MTCC 2414 Using Agroresidues as a Potential Substrate

Laccases are the model enzymes for multicopper oxidases and participate in several applications such as bioremediation, biopulping, textile, and food industries. Laccase producing bacterium, Bacillus subtilis MTCC 2414, was subjected to optimization by conventional techniques and was partially purified using ammonium salt precipitation method. The agroresidue substrates used for higher yield of laccase were rice bran and wheat bran. Maximum production was achieved at temperature 30°C (270 ± 2.78 U/mL), pH 7.0 (345 ± 3.14 U/mL), and 96 h (267 ± 2.64 U/mL) of incubation. The carbon and nitrogen sources resulted in high enzyme yield at 3% sucrose (275 ± 3.11 U/mL) and 3% peptone (352.2 ± 4.32 U/mL) for rice bran and 3% sucrose (247.4 ± 3.51 U/mL) and 3% peptone (328 ± 3.33 U/mL) for wheat bran, respectively. The molecular weights of partially purified laccase were 52 kDa for rice bran and 55 kDa for wheat bran. The laccase exhibited optimal activity at 70°C (260.3 ± 6.15 U/mL), pH 9.0 (266 ± 4.02 U/mL), and metal ion CuSO4 (141.4 ± 6.64) was found to increase the production. This is the first report that delivers the higher yield of laccase produced from B. subtilis MTCC 2414 using agroresidues as a potential substrate.

Aromatic metabolism of filamentous fungi in relation to the presence of aromatic compounds in plant biomass

The biological conversion of plant lignocellulose plays an essential role not only in carbon cycling in terrestrial ecosystems but also is an important part of the production of second generation biofuels and biochemicals. The presence of the recalcitrant aromatic polymer lignin is one of the major obstacles in the biofuel/biochemical production process and therefore microbial degradation of lignin is receiving a great deal of attention. Fungi are the main degraders of plant biomass, and in particular the basidiomycete white rot fungi are of major importance in converting plant aromatics due to their ability to degrade lignin. However, the aromatic monomers that are released from lignin and other aromatic compounds of plant biomass are toxic for most fungi already at low levels, and therefore conversion of these compounds to less toxic metabolites is essential for fungi. Although the release of aromatic compounds from plant biomass by fungi has been studied extensively, relatively little attention has been given to the metabolic pathways that convert the resulting aromatic monomers. In this review we provide an overview of the aromatic components of plant biomass, and their release and conversion by fungi. Finally, we will summarize the applications of fungal systems related to plant aromatics.

Biodegradation of azo dyes acid red 183, direct blue 15 and direct red 75 by the isolate Penicillium oxalicum SAR-3

Soils contaminated with dyes were collected and screened for obtaining potential fungal strains for the degradation of azo dyes. A strain that demonstrated broad spectrum ability for catabolizing different azo dyes viz. Acid Red 183 (AR 183), Direct Blue 15 (DB 15) and Direct Red 75 (DR 75) at 100 mg L(-1) concentration was subsequently identified as Penicillium oxalicum SAR-3 based on 18S and internal transcribed spacer (ITS) rDNA gene sequence analysis. The strain has shown remarkably higher levels of degradation (95-100%) for almost all the dyes within 120 h at 30°C at pH 7.0. Notable levels of manganese peroxidase (659.4 ± 20 UL(-1)) during dye decolorization indicated the involvement of this enzyme in the decolorization process. The dyes following decolorization were catabolized as evident by spectroscopic analyses.

Decolorization of the metal textile dye Lanaset Grey G by immobilized white-rot fungi

In this paper we studied the ability of four Tunisian-isolated fungi (i.e. Coriolopsis gallica, Bjerkandera adusta, Trametes versicolor and Trametes trogii) immobilized into Ca-alginate beads to decolorize the metal textile dye Lanaset Grey G (LG). The effect of different operational conditions, such as initial dye concentration, temperature, pH, beads/medium ratio and agitation, on dye decolorization by the immobilized fungi was investigated. Maximal decolorization percentages of 88.7%, 89.3%, 82.1% and 81.3% for C. gallica, B. adusta, T. versicolor and T. trogii were attained, respectively, when operating at an initial LG concentration of 150 mg/L, pH values of 5.0-6.0, temperatures of 40-45 °C and a beads/medium ratio of 20% (w/v) in static conditions after 72 h of incubation. Subsequently, the re-usability of the immobilized fungi was evaluated. After three decolorization cycles, the decolorization percentage of free cell cultures dropped to values below 36%, while decolorization percentages of about 75%, 70%, 60% and 68% were obtained by the immobilized cultures of C. gallica, B. adusta, T. versicolor and T. trogii, respectively.

Lignin degradation by selected fungal species

As biological decomposition of plant biomass represents a popular alternative environmental-friendly and economically justified process, screening of ligninolytic enzyme systems of various fungal species is a topical study area. The goal of the study was to obtain clear insight into the dynamics of laccase, Mn-dependent peroxidase, and Mn-independent peroxidase activity and levels of wheat straw lignin degradation in seven wood-rotting fungi. The best laccase producers were Pleurotus ostreatus and Pleurotus eryngii. Lenzites betulinus and Fomitopsis pinicola were the best Mn-dependent peroxidase producers, and P. ostreatus the weakest one. The peak of Mn-independent peroxidase was noted in Dichomytus squalens, and the minimum value in P. ostreatus. The profiles of the three enzymes, obtained by isoelectric focusing, were variable depending on the species and cultivation period. D. squalens was the best lignin degrader (34.1% of total lignin amount), and P. ostreatus and P. eryngii the weakest ones (7.1% and 14.5%, respectively).

Influence of ligninolytic enzymes on straw saccharification during fungal pretreatment

Solid state and submerged fermentations in the presence of white-rot basidiomycetes (Bjerkandera adusta, Fomes fomentarius, Ganoderma resinaceum, Irpex lacteus, Phanerochaete chrysosporium, Trametes versicolor and basidiomycete Euc-1) and the litter-decomposing basidiomycete Lepista nuda were evaluated as a pretreatment to increase enzymatic saccharification of wheat straw. Enzymatic hydrolysis of holocellulose after solid state pretreatment showed a significant (P<0.05) increase of saccharification process for T. versicolor, Euc-1, G. resinaceum and I. lacteus, being T. versicolor (strain Tv2) the best one with a sugar yield increase of 91% compared with untreated straw. In submerged medium the pretreatment with I. lacteus, Euc-1 and P. chrysosporium enhanced saccharification but at a lesser extent. Covariance analysis was used to evaluate the relationships between ligninolytic enzymes (lignin peroxidase, manganese-dependent peroxidase and laccase) and saccharification increase. Results showed that only the presence of lignin peroxidase during pretreatment can lead to a significant (P<0.05) increase in the saccharification yield.

Immobilized laccase on a new cryogel carrier and kinetics of two anthraquinone derivatives oxidation

A coordinatively immobilized laccase was prepared using a new cryogel type carrier. The support has a wide-pore texture facilitating diffusion of different substrates to the enzyme reaction center. The biocatalyst proved to be efficient in decolorization of two anthraquinone derivatives, namely Acid Blue 62 and bromaminic acid. After 24 h over 80% of the two substrates have been oxidated. The kinetic data (K (m) and V (max)) for the oxidation of the two anthraquinone derivatives, with the free and immobilized enzyme, have been determined and compared. Other parameters, like k (cat) and the specificity constant have been calculated and analyzed. The influence of substrate properties (hydrophobicity, polarity, etc.) has been discussed.

Lignolytic Enzymes of a Mushroom Stereum ostrea Isolated from Wood Logs

Production of lignolytic enzymes by the mushroom fungus Stereum ostrea in liquid medium under conditions of vegetative growth was examined for 10 days in comparison to the reference culture Phanerochaete chrysosporium. Though growth and secretion of extracellular protein by S. ostrea were comparable to those of P. chrysosporium, yields of laccase enzyme by S. ostrea were higher than laccase titres of P. chrysosporium by more than 2 folds on the peak production time interval (IVth day of incubation). S. ostrea yielded titres of 25 units of laccase/ml as against 8.9 units of laccase/ml on the IVth day of incubation. Stereum ostrea also exhibited activities of other lignolytic enzymes, lignin peroxidase (LiP) and manganese peroxidase (MnP), higher than the reference culture. Growth of S. ostrea on the medium in the presence of Remazol orange 16 resulted in the decolourisation of dye, confirming the presence of lignolytic enzymes. S. ostrea appears to be a promising culture with complete lignolytic system.

The Use of HRP in Decolorization of Reactive Dyes and Toxicological Evaluation of Their Products

This work studied the potential use of horseradish peroxidase (HRP) in the decolorization of the following textile dyes: Drimarene Blue X-3LR (DMBLR), Drimarene Blue X-BLN (DMBBLN), Drimarene Rubinol X-3LR (DMR), and Drimarene Blue CL-R (RBBR). Dyes were individually tested in the reaction media containing 120 mg·L⁻¹, considering the following parameters: temperature (20–45°C), H₂O₂ concentration (0–4.44 mmol·L⁻¹), and reaction time (5 minutes, 1 and 24 h). The following conditions: 35°C, 0.55 mmol·L⁻¹, and 1h, provided the best set of results of color removal for DMBLR (99%), DMBBLN (77%), DMR (94%), and RBBR (97%). It should be mentioned that only 5 minutes of reaction was enough to obtain 96% of decolorization for DMBLR and RBBR. After the decolorization reactions of DMBLR, DMR, and RBBR, it was possible to observe the reduction of Artemia salina mortality and the no significant increase in toxicity for the products generated from DMBBLN.

Production of Ligninolytic Enzymes by White-Rot FungusDatroniasp. KAPI0039 and Their Application for Reactive Dye Removal

This study focused on decolorization of 2 reactive dyes; Reactive Blue 19 (RBBR) and Reactive Black 5 (RB5), by selected white-rot fungusDatroniasp. KAPI0039. The effects of reactive dye concentration, fungal inoculum size as well as pH were studied. Samples were periodically collected for the measurement of color unit, Laccase (Lac), Manganese Peroxidase (MnP), and Lignin Peroxidase (LiP) activity. Eighty-six percent of 1,000 mg L−1RBBR decolorization was achieved by 2% (w/v)Datroniasp. KAPI0039 at pH 5. The highest Lac activity (759.81 UL−1) was detected in the optimal condition. For RB5,Datroniasp. KAPI0039 efficiently performed (88.01% decolorization) at 2% (w/v) fungal inoculum size for the reduction of 600 mg L−1RB5 under pH 5. The highest Lac activity (178.57 UL−1) was detected, whereas the activity of MnP and LiP was absent during this hour. The result, therefore, indicated thatDatroniasp. KAPI0039 was obviously able to breakdown both reactive dyes, and Lac was considered as a major lignin-degradation enzyme in this reaction.