Cloning, expression and phylogenetic analysis of a divergent laccase multigene family in Auricularia auricula-judae

Genome-wide analysis of the Pleurotus eryngii laccase gene (PeLac) family and functional identification of PeLac5

The laccase gene family encodes multiple isozymes that are crucial for the degradation of substrates and the regulation of developmental processes in fungi. Pleurotus eryngii is an important edible and medicinal fungus belonging to the Basidiomycota phylum and can grow on a variety of natural substrates. In the present study, genome-wide profiling of P. eryngii identified 10 genes encoding its laccase isoenzymes. Conservative sequence analysis demonstrated that all PeLacs possess classical laccase structural domains. Phylogenetic analysis yielded four major subgroups, the members of which are similar with respect to conserved gene organization, protein domain architecture, and consensus motifs. The 10 PeLacs formed three groups together with 12 PoLacs in Pleurotus ostreatus, indicating that they share a high level of evolutionary homology. Cis-responsive element analysis implied that PeLacs genes play a role in growth and development and lignocellulose degradation. Targeted overexpression of PeLac5 reduced the time to primordia formation and their development to fruiting bodies. Gene expression patterns in the presence of different lignocellulosic substrates indicate that three PeLacs genes (2, 4, and 9) are key to lignocellulose degradation. This work presents the first inventory of laccase genes in P. eryngii and preliminarily explores their functions, which may help to uncover the manner by which these proteins utilize substrates.

Expression profiling of laccase and β-glucan synthase genes in Pleurotus ostreatus during different developmental stages

BACKGROUND

Pleurotus ostreatus, commonly known as the oyster mushroom, is a saprophytic fungus with many applications in biotechnology and medicine. This mushroom is a rich source of proteins, polysaccharides, and bioactive compounds that have been shown to possess anticancer, antioxidant, and immunomodulatory properties. In this study, we investigated the expression profile of laccase (POXA3) and β-glucan synthase (FKS) genes during different developmental stages in two strains of P. ostreatus.

METHODS AND RESULTS

Cultural and morphological studies of the two strains were studied. DMR P115 strain recorded faster mycelial growth compared to the HUC strain. However, both strains produced white, thick fluffy mycelial growth with radiating margin. Morphological characteristics of the mushroom fruiting body were also higher in the DMR P115 strain. The expression of these genes was analyzed using quantitative real-time PCR (qPCR) and the results were compared to those of the reference gene β-actin. The expression of laccase (POXA3) was higher in the mycelial stage of DMR P115 and HUC strains indicating its role in the fruiting body development and substrate degradation. The expression of β-glucan synthase (FKS) was upregulated in the mycelium and mature fruiting body of the DMR P115 strain. In contrast, there was only significant upregulation in the mycelial stage of the HUC strain, which indicates its role in cell wall formation and the immunostimulatory properties of that strain.

CONCLUSION

The results deepen the understanding of the molecular mechanism of the fruiting body development in P. ostreatus and can be used as a foundation for future lines of research related to strain improvement of P. ostreatus.

Research progress of Auricularia heimuer on cultivation physiology and molecular biology

Auricularia heimuer (A. heimuer F. Wu, B. K. Cui, Y. C. Dai), a well-known gelatinous fungus used for both food and medicine, is a major edible fungus with a more than 1000-year history of cultivation in China. The nutrients of A. heimuer are abundant, including polysaccharides, melanin, mineral elements, etc. The A. heimuer polysaccharides exhibit antioxidant, immunomodulatory, and anticancer properties. A. heimuer is a completely different species grown in China, unlike Auricularia auricula-judae (Bull.) Quel, which was used to characterize it. The cultivated strain varies based on the local climatic factors and cultivation practices. Hardwood chips are the primary material utilized in the cultivation of substitute materials, which is the principal cultivation technique. However, in actual production, straw is frequently replaced for some wood chips to address the issue of a lack of wood. There are three different types of growing techniques: open-air ground cultivation, arch cultivation, and shed-type hanging substitute cultivation of these three, the quality of A. heimuer grown in a shed is superior to that grown in an open-air environment. The A. heimuer genome sequencing project started later than expected, and the entire genome sequencing was not finished until 2019. A. heimuer’s molecular biology studies have mostly concentrated on analyzing genetic diversity and identifying cultivars using molecular markers including RAPD, ISSR, and ITS. There have only been a small number of studies on the function of A. heimuer genes, which have only focused on the preliminary cloning and expression study of a few genes, including the laccase gene and the triterpene compound production gene, among others. However, there is still a lack of comprehensive information concerning A. heimuer, necessitating a synopsis. To our knowledge, this is the first published review of A. heimuer, and it summarizes the most recent studies on its molecular biology and cultivation. This review can serve as a guide for future research on the fungus.

A novel fungal negative-stranded RNA virus related to mymonaviruses in Auricularia heimuer

Here, we report the characterization of a novel (-)ssRNA mycovirus isolated from Auricularia heimuer CCMJ1222, using a combination of RNA-seq, reverse transcription polymerase chain reaction, 5' and 3' rapid amplification of cDNA ends, and Sanger sequencing. Based on database searches, sequence alignment, and phylogenetic analysis, we designated the virus as "Auricularia heimuer negative-stranded RNA virus 1" (AhNsRV1). This virus has a monopartite RNA genome related to mymonaviruses (order Mononegavirales). The AhNsRV1 genome consists of 11,441 nucleotides and contains six open reading frames (ORFs). The largest ORF encodes a putative RNA-dependent RNA polymerase; the other ORFs encode hypothetical proteins with no conserved domains or known function. AhNsRV1 is the first (-)ssRNA virus and the third virus known to infect A. heimuer.

Recent Advances in Synthesis and Degradation of Lignin and Lignin Nanoparticles and Their Emerging Applications in Nanotechnology

Lignin is an important commercially produced polymeric material. It is used extensively in both industrial and agricultural activities. Recently, it has drawn much attention from the scientific community. It is abundantly present in nature and has significant application in the production of biodegradable materials. Its wide usage includes drug delivery, polymers and several forms of emerging lignin nanoparticles. The synthesis of lignin nanoparticles is carried out in a controlled manner. The traditional manufacturing techniques are costly and often toxic and hazardous to the environment. This review article highlights simple, safe, climate-friendly and ecological approaches to the synthesis of lignin nanoparticles. The changeable, complex structure and recalcitrant nature of lignin makes it challenging to degrade. Researchers have discovered a small number of microorganisms that have developed enzymatic and non-enzymatic metabolic pathways to use lignin as a carbon source. These microbes show promising potential for the biodegradation of lignin. The degradation pathways of these microbes are also described, which makes the study of biological synthesis much easier. However, surface modification of lignin nanoparticles is something that is yet to be explored. This review elucidates the recent advances in the biodegradation of lignin in the ecological system. It includes the current approaches, methods for modification, new applications and research for the synthesis of lignin and lignin nanoparticles. Additionally, the intricacy of lignin’s structure, along with its chemical nature, is well-described. This article will help increase the understanding of the utilization of lignin as an economical and alternative-resource material. It will also aid in the minimization of solid waste arising from lignin.

Transcriptome analysis of Auricularia fibrillifera fruit-body responses to drought stress and rehydration

BACKGROUND

Drought stress severely restricts edible fungus production. The genus Auricularia has a rare drought tolerance, a rehydration capability, and is nutrient rich.

RESULTS

The key genes and metabolic pathways involved in drought-stress and rehydration were investigated using a transcriptome analysis to clarify the relevant molecular mechanisms. In total, 173.93 Mb clean reads, 26.09 Gb of data bulk, and 52,954 unigenes were obtained. Under drought-stress and rehydration conditions, 14,235 and 8539 differentially expressed genes, respectively, were detected. 'Tyrosine metabolic', 'caffeine metabolism', 'ribosome', 'phagosome', and 'proline and arginine metabolism', as well as 'peroxisome' and 'mitogen-activated protein kinase signaling' pathways, had major roles in A. fibrillifera responses to drought stress. 'Tyrosine' and 'caffeine metabolism' might reveal unknown mechanisms for the antioxidation of A. fibrillifera under drought-stress conditions. During the rehydration process, 'diterpenoid biosynthesis', 'butanoate metabolism', 'C5-branched dibasic acid', and 'aflatoxin biosynthesis' pathways were significantly enriched. Gibberellins and γ-aminobutyric acid were important in the recovery of A. fibrillifera growth after rehydration. Many genes related to antibiotics, vitamins, and other health-related ingredients were found in A. fibrillifera.

CONCLUSION

These findings suggested that the candidate genes and metabolites involved in crucial biological pathways might regulate the drought tolerance or rehydration of Auricularia, shedding light on the corresponding mechanisms and providing new potential targets for the breeding and cultivation of drought-tolerant fungi.

Biodegradation of sulfonamide antibiotics through the heterologous expression of laccases from bacteria and investigation of their potential degradation pathways

In this study, seven laccase genes from different bacteria were linked with the signal peptides PelB, Lpp or Ompa for heterologous expression in E. coli. The recombinant strains were applied for the removal of sulfadiazine (SDZ), sulfamethazine (SMZ), and sulfamethoxazole (SMX). The results obtained for different signal peptides did not provide insights into the removal mechanism. The removal ratios of SDZ, SMZ, and SMX obtained with the recombinant strain 6#P at 60 h were around 92.0%, 89.0%, and 88.0%, respectively. The degradation pathways of sulfonamides have been proposed, including SO₂ elimination, hydroxylation, oxidation, pyrimidine ring cleavage, and N-S bond cleavage. Different mediators participate in the degradation of antibiotics through different mechanisms, and different antibiotics have different responses to the same mediator. The addition of 2,2'-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) slightly promoted the removal of sulfonamides by most recombinant strains with different signal peptides, especially for the recombinant strain 2#O. The removal of sulfonamides by 1-hydroxybenzotriazole (HBT) varied with the recombinant strains. Syringaldehyde (SA) had a slight inhibitory effect on the removal of sulfonamides, with the most significant effect on strains 7#L and 7#O.

Discovery of two novel laccase-like multicopper oxidases from Pleurotus citrinopileatus and their application in phenolic oligomer synthesis

BACKGROUND

Laccases and laccase-like multicopper oxidases (LMCOs) oxidize a vast array of phenolic compounds and amines, releasing water as a byproduct. Their low substrate specificity is responsible for their tremendous biotechnological interest, since they have been used for numerous applications. However, the laccases characterized so far correspond to only a small fraction of the laccase genes identified in fungal genomes. Therefore, the knowledge regarding the biochemistry and physiological role of minor laccase-like isoforms is still limited.

RESULTS

In the present work, we describe the isolation, purification and characterization of two novel LMCOs, PcLac1 and PcLac2, from Pleurotus citrinopileatus. Both LMCOs were purified with ion-exchange chromatographic methods. PcLac2 was found to oxidize a broader substrate range than PcLac1, but both LMCOs showed similar formal potentials, lower than those reported previously for laccases from white-rot fungi. Proteomic analysis of both proteins revealed their similarity with other well-characterized laccases from Pleurotus strains. Both LMCOs were applied to the oxidation of ferulic and sinapic acid, yielding oligomers with possible antioxidant activity.

CONCLUSIONS

Overall, the findings of the present work can offer new insights regarding the biochemistry and variability of low-redox potential laccases of fungal origin. Low-redox potential biocatalysts could offer higher substrate selectivity than their high-redox counterparts, and thus, they could be of applied value in the field of biocatalysis.

Alternative Splicing of Heat Shock Transcription Factor 2 Regulates the Expression of Laccase Gene Family in Response to Copper in Trametes trogii

White-rot fungi, especially Trametes strains, are the primary source of industrial laccases in bioenergy and bioremediation. Trametes strains express members of the laccase gene family with different physicochemical properties and expression patterns. However, the literature on the expression pattern of the laccase gene family in T. trogii S0301 and the response mechanism to Cu²⁺, a key laccase inducer, in white-rot fungal strains is scarce. In the present study, we found that Cu²⁺ could induce the mRNAs and proteins of the two alternative splicing variants of heat shock transcription factor 2 (TtHSF2). Furthermore, the overexpression of alternative splicing variants TtHSF2α and TtHSF2β-I in the homokaryotic T. trogii S0301 strain showed opposite effects on the extracellular total laccase activity, with the maximum laccase activity of approximately 0.6 U mL^-1 and 3.0 U mL^-1, respectively, on the eighth day, which is 0.4 and 2.3 times that of the wild type strain. Similarly, TtHSF2α and TtHSF2β-I play opposite roles in the oxidation tolerance to H₂O₂ In addition, the direct binding of TtHSF2α to the promoter regions of the representative laccase isoenzymes (TtLac1 and TtLac13) and protein-protein interactions between TtHSF2α and TtHSF2β-I were detected. Our results demonstrate the crucial roles of TtHSF2 and its alternative splicing variants in response to Cu²⁺ We believe that these findings will deepen our understanding of alternative splicing of HSFs and their regulatory mechanism of the laccase gene family in white-rot fungi.Importance The members of laccase gene family in Trametes strains are the primary source of industrial laccase and have gained widespread attention. Increasing the yield and enzymatic properties of laccase through various methods has always been a topic worthy of attention, and there is no report on the regulation of laccase expression through HSF transcription factor engineering. Here, we found that two alternative splicing variants of TtHSF2 functioned oppositely in regulating the expression of laccase genes, and copper can induce the expression of almost all members of the laccase gene family. Most importantly, our study suggested that TtHSF2 and its alternative splicing variants are vital for copper-induced production of laccases in T. trogii S0301.

The development of an efficient RNAi system based on Agrobacterium-mediated transformation approach for studying functional genomics in medical fungus Wolfiporia cocos

Genetic transformation methods reported for Wolfiporia cocos are limited. In this study, we describe an efficient RNA interference (RNAi) system based on Agrobacterium-mediated transformation approach in W. cocos for the first time. Actively growing mycelial plugs were used as recipients for transformation using endogenous orotidine-5'-phosphate decarboxylase gene (URA3) as both a selective marker and a silencing gene, under the control of the dual promoters of Legpd and Leactin from Lentinula edodes and the single promoter of Wcgpd from W. cocos, respectively. The results showed that both the two kinds of promoters effectively drive the expression of URA3 gene, and the URA3-silenced transformants could be selected on CYM medium containing 5'-fluoroorotic acid. In addition, silencing URA3 gene has no effect on the growth of W. cocos hyphae. The incomplete silencing of the URA3 locus was also observed in this study. This study will promote further study on the mechanism of substrate degradation, sclerotial formation, and biosynthesis network of pharmacological compounds in W. cocos.

Molecular characteristics of a novel ssRNA virus isolated from Auricularia heimuer in China

A novel positive-sense single-stranded RNA virus was isolated from strain CCMJ1271 of the fungus Auricularia heimuer, and the complete genome sequence of the virus was determined. Database searching, sequence alignment, and phylogenetic analysis revealed that this fungal virus and some viruses of family Virgaviridae clustered into a single branch of a phylogenetic tree, and we thus tentatively named the virus "Auricularia heimuer mycovirgavirus 1" (AhMV1). The AhMV1 genome consists of 9,934 nucleotides and contains a short poly(A) tail and three open reading frames (ORFs). ORF1 encodes an RNA-dependent RNA polymerase (RdRp), ORF2 encodes a protein that is homologous to movement proteins of plant virgaviruses, and ORF3 encodes a coat protein (CP). AhMV1 is the first virus to be discovered in A. heimuer.

Exploiting the potential of metal and solvent tolerant laccase from Tricholoma giganteum AGDR1 for the removal of pesticides

Laccase from previously reported hardwood degrading fungus, Tricholoma giganteum AGDR1, was isolated, identified at molecular level, biochemically characterized and also utilized for pesticide degradation. Laccase gene is comprised of 3752 bp, which encompassed 742-bp of 5' flanking upstream sequence with 12 introns and 12 exons. Mature enzyme possesses 391 amino acids and signal peptide, which is determined to be monomeric protein with an apparent molecular weight of 41 kDa and 6.45 pI. Higher optimal activities were observed at 45 °C and pH 3.0 and surprisingly, it exhibited more than 20% of relative activity at pH 1.5. Purified laccase was tolerant to 100 mM of metals (i.e. Se, Pb, Cu, Cr and Cd), organic solvents (ethyl acetate, methanol, ethanol and acetone) and potent inhibitors (hydroxylamine, thiourea, NaF and Na-azide) as compared to reported laccases. It was able to degrade 29%, 7% and 72% of chlorpyrifos, profenofos and thiophanate methyl within 15 h, respectively. Molecular docking analysis revealed that higher binding efficacy of these pesticides is observed with H83, H320, A95, V384, and P366 which are presented near to the catalytic site. Based on the results, T. giganteum AGDR1 laccase can be applied for the potential remediation and industrial applications under harsh conditions.

Purification and characterization of a fungal laccase from the ascomycete Thielavia sp. and its role in the decolorization of a recalcitrant dye

A laccase-producing ascomycete was isolated from arid soil in Tunisia. This fungus was identified as Thielavia sp. using the phylogenetic analysis of rDNA internal transcribed spacers. The extracellular laccase produced by the fungus was purified to electrophoretic homogeneity, showing a molecular mass around 70 kDa. The enzyme had an optimum pH of 5.0 and 6.0 for ABTS and 2,6‑DMP, respectively and it showed remarkable high thermal stability, showing its optimal temperature at 70 °C (against 2,6‑DMP). It presented slight inhibiting effect by EDTA, SDS and l‑cyst although this effect was more marked by sodium azide (0.1 mM). On the other hand, it showed tolerance to up to 300 mM NaCl, retaining around 50% of its activity at 900 mM. Among the metal ions tested on TaLac1, Mn²⁺ showed an activating effect. Their kinetic parameters K_m and k_cat were 23.7 μM and 4.14 s^-1 for ABTS, and 24.3 μM and 3.46 s^-1 towards 2,6‑DMP. The purified enzyme displayed greater efficiency in Remazol Brilliant Blue R decolorization (90%) in absence of redox mediator, an important property for biotechnological applications.

The heat shock protein 40 LeDnaJ regulates stress resistance and indole-3-acetic acid biosynthesis in Lentinula edodes

DnaJ proteins, termed heat shock proteins based on their molecular weight, function as molecular chaperones that play critical roles in regulating organism growth and development as well as adaptation to the environment. However, little has been reported on their gene function in higher basidiomycetes. Here, the heat shock protein 40 (LeDnaJ) gene was cloned and characterized from Lentinula edodes. RNA interference was used to explore the function of LeDnaJ in response to heat stress and Trichoderma atroviride. Integration of the target gene into the L. edodes genome was confirmed by Southern blot analysis, and the silence efficiency of LeDnaJ was analyzed by qRT-PCR. The results revealed that LeDnaJ silence caused defects in mycelial growth and resistance to heat stress and T. atroviride, but increased the mycelial density compared with the wild type (WT) strain S606. Additionally, the IAA content showed a more than 10-fold increase in the WT after heat stress, but an about two-fold increase in the two LeDnaJ RNAi transfortants (LeDnaJ-i-6 and LeDnaJ-i-8). Previous study has shown that enhanced IAA (indole-3-acetic acid) content enhanced the thermotolerance of the heat-sensitive strain YS3357. In this study, it was documented that IAA amendments could partly restore the resistance to T. atroviride and thermotolerance of the two LeDnaJ RNAi transformants. Overall, LeDnaJ is nvolved in fungal growth, T. atroviride resistance, and thermotolerance by regulating the IAA biosynthesis in L. edodes.

Systematic Analysis of the Pleurotus ostreatus Laccase Gene (PoLac) Family and Functional Characterization of PoLac2 Involved in the Degradation of Cotton-Straw Lignin

Fungal laccases play important roles in the degradation of lignocellulose. Although some PoLacs have been reported in several studies, still no comprehensive bioinformatics study of the LAC family in Pleurotus ostreatus has been reported. In this study, we identified 12 laccase genes in the whole genome sequence of P. ostreatus and their physical characteristics, gene distribution, phylogenic relationships, gene structure, conserved motifs, and cis-elements were also analyzed. The expression patterns of 12 PoLac genes at different developmental stages and under different culture substrates were also analyzed. The results revealed that PoLac2 and PoLac12 may be involved in the degradation of lignin and the formation of the fruiting body, respectively. Subsequently, we overexpressed PoLac2 in P. ostreatus by the Agrobacterium tumefaciens-mediated transformation (ATMT) method. The transformants' laccase activity increased in varying degrees, and the gene expression level of PoLac2 in transformants was 2-8 times higher than that of the wild-type strain. Furthermore, the lignin degradation rate by transgenic fungus over 30 days was 2.36-6.3% higher than that of wild-type. Our data show that overexpression of PoLac2 significantly enhanced the lignin degradation of cotton-straw. To our knowledge, this study is the first report to demonstrate the functions of PoLac2 in P. ostreatus.

Importance of a Laccase Gene (Lcc1) in the Development of Ganoderma tsugae

In this study, a novel laccase gene (Lcc1) from Ganoderma tsugae was isolated and its functions were characterized in detail. The results showed that Lcc1 has the highest expression activity during mycelium development and fruit body maturation based on the analysis of Lcc1 RNA transcripts at different developmental stages of G. tsugae. To investigate the exact contribution of Lcc1 to mycelium and fruit body development in G. tsugae, Lcc1 transgenic strains were constructed by targeted gene replacement and over-expression approaches. The results showed that the lignin degradation rate in Lcc1 deletion mutant was much lower than the degradation efficiency of the wild-type (WT), over-expression and rescue strains. The lignin degradation activity of G. tsugae is dependent on Lcc1 and the deletion of Lcc1 exerted detrimental influences on the development of mycelium branch. Furthermore, the study uncovered that Lcc1 deletion mutants generated much shorter pale grey fruit bodies, suggesting that Lcc1 contributes directly to pigmentation and stipe elongation during fruit body development in G. tsugae. The information obtained in this study provides a novel and mechanistic insight into the specific role of Lcc1 during growth and development of G. tsugae.

A halotolerant laccase from Chaetomium strain isolated from desert soil and its ability for dye decolourization

A novel fungal laccase produced by the ascomycete Chaetomium sp. isolated from arid soil was purified and characterized and its ability to remove dyes was determined. Extracellular laccase was purified 15-fold from the crude culture to homogeneity with an overall yield of 50% using ultrafiltration and anion-exchange chromatography. The purified enzyme was found to be a monomeric protein with a molecular mass of 68 kDa, estimated by SDS-PAGE, and with an isoelectric point of 5.5. The optimal temperature and pH value for laccase activity toward 2,6-DMP were 60 °C and 3.0, respectively. It was stable at temperatures below 50 °C and at alkaline conditions. Kinetic study showed that this laccase showed higher affinity on ABTS than on 2,6-DMP. Its activity was enhanced by the presence of several metal ions such as Mg2+, Ca2+ and Zn2+, while it was strongly inhibited by Fe2+, Ag+ and Hg2+. The novel laccase also showed high, remarkable sodium chloride tolerance. Its ability to decolorize different dyes, with or without HBT (1-hydroxy-benzotriazole), as redox mediator, suggests that this protein may be useful for different industrial applications and/or bioremediation processes.

Construction of a genetic linkage map and QTL mapping of agronomic traits in Auricularia auricula-judae

Auricularia auricula-judae is a traditional edible fungus that is cultivated widely in China. In this study, a genetic linkage map for A. auricula-judae was constructed using a mapping population consisting of 138 monokaryons derived from a hybrid strain (A119-5). The monokaryotic parent strains A14-5 and A18-119 were derived from two cultivated varieties, A14 (Qihei No. 1) and A18 (Qihei No. 2), respectively. In total, 130 simple sequence repeat markers were mapped. These markers were developed using the whole genome sequence of A. auricula-judae and amplified in A14-5, A18- 119, and the mapping population. The map consisted of 11 linkage groups (LGs) spanning 854 cM, with an average interval length of 6.57 cM. A testcross population was derived from crossing between the monokaryon A184-57 (from the wild strain A184 as a tester strain) and the mapping population. Important agronomic trait-related QTLs, including mycelium growth rate on potato dextrose agar for the mapping population, mycelium growth rate on potato dextrose agar and sawdust for the testcross population, growth period (days from inoculation to fruiting body harvesting), and yield for the testcross population, were identified using the composite interval mapping method. Six mycelium growth raterelated QTLs were identified on LG1 and LG4, two growth period-related QTLs were identified on LG2, and three yieldrelated QTLs were identified on LG2 and LG6. The results showed no linkage relationship between mycelium growth rate and growth period. The present study provides a foundation for locating genes for important agronomic characteristics in A. auricula-judae in the future.

Laccases: Production, Expression Regulation, and Applications in Pharmaceutical Biodegradation

Laccases are a family of copper-containing oxidases with important applications in bioremediation and other various industrial and biotechnological areas. There have been over two dozen reviews on laccases since 2010 covering various aspects of this group of versatile enzymes, from their occurrence, biochemical properties, and expression to immobilization and applications. This review is not intended to be all-encompassing; instead, we highlighted some of the latest developments in basic and applied laccase research with an emphasis on laccase-mediated bioremediation of pharmaceuticals, especially antibiotics. Pharmaceuticals are a broad class of emerging organic contaminants that are recalcitrant and prevalent. The recent surge in the relevant literature justifies a short review on the topic. Since low laccase yields in natural and genetically modified hosts constitute a bottleneck to industrial-scale applications, we also accentuated a genus of laccase-producing white-rot fungi, Cerrena, and included a discussion with regards to regulation of laccase expression.

Laccase Gene Family in Cerrena sp. HYB07: Sequences, Heterologous Expression and Transcriptional Analysis

Laccases are a class of multi-copper oxidases with industrial potential. In this study, eight laccases (Lac1-8) from Cerrena sp. strain HYB07, a white-rot fungus with high laccase yields, were analyzed. The laccases showed moderate identities to each other as well as with other fungal laccases and were predicted to have high redox potentials except for Lac6. Selected laccase isozymes were heterologously expressed in the yeast Pichia pastoris, and different enzymatic properties were observed. Transcription of the eight laccase genes was differentially regulated during submerged and solid state fermentation, as shown by quantitative real-time polymerase chain reaction and validated reference genes. During 6-day submerged fermentation, Lac7 and 2 were successively the predominantly expressed laccase gene, accounting for over 95% of all laccase transcripts. Interestingly, accompanying Lac7 downregulation, Lac2 transcription was drastically upregulated on days 3 and 5 to 9958-fold of the level on day 1. Consistent with high mRNA abundance, Lac2 and 7, but not other laccases, were identified in the fermentation broth by LC-MS/MS. In solid state fermentation, less dramatic differences in transcript abundance were observed, and Lac3, 7 and 8 were more highly expressed than other laccase genes. Elucidating the properties and expression profiles of the laccase gene family will facilitate understanding, production and commercialization of the fungal strain and its laccases.

Purification and Characterization of a White Laccase with Pronounced Dye Decolorizing Ability and HIV-1 Reverse Transcriptase Inhibitory Activity from Lepista nuda

A strain LN07 with high laccase yield was identified as basidiomycete fungus Lepista nuda from which a white laccase without type I copper was purified and characterized. The laccase was a monomeric protein with a molecular mass of 56 kDa. Its N-terminal amino acid sequence was AIGPAADLHIVNKDISPDGF. Besides, eight inner peptide sequences were determined and lac4, lac5 and lac6 sequences were in the Cu²⁺ combination and conservation zones of laccases. HIV-1 reverse transcriptase was inhibited by the laccase with a half-inhibitory concentration of 0.65 μM. Cu²⁺ ions (1.5 mM) enhanced the laccase production and the optimal pH and temperature of the laccase were pH 3.0 and 50 °C, respectively. The Km and Vmax of the laccase using ABTS as substrate were respectively 0.19 mM and 195 μM. Several dyes including laboratory dyes and textile dyes used in this study, such as Methyl red, Coomassie brilliant blue, Reactive brilliant blue and so on, were decolorized in different degrees by the purified laccase. By LC-MS analysis, Methyl red was structurally degraded by the laccase. Moreover, the laccase affected the absorbance at the maximum wavelength of many pesticides. Thus, the white laccase had potential commercial value for textile finishing and wastewater treatment.

Identification and characterization of laccase-type multicopper oxidases involved in dye-decolorization by the fungus Leptosphaerulina sp

Background

Fungal laccases are multicopper oxidases (MCOs) with high biotechnological potential due to their capability to oxidize a wide range of aromatic contaminants using oxygen from the air. Albeit the numerous laccase-like genes described in ascomycete fungi, ascomycete laccases have been less thoroughly studied than white-rot basidiomycetous laccases. A variety of MCO genes has recently been discovered in plant pathogenic ascomycete fungi, however little is known about the presence and function of laccases in these fungi or their potential use as biocatalysts. We aim here to identify the laccase-type oxidoreductases that might be involved in the decolorization of dyes by Leptosphaerulina sp. and to characterize them as potential biotechnological tools.

Results

A Leptosphaerulina fungal strain, isolated from lignocellulosic material in Colombia, produces laccase as the main ligninolytic oxidoreductase activity during decolorization of synthetic organic dyes. Four laccase-type MCO genes were partially amplified from the genomic DNA using degenerate primers based on laccase-specific signature sequences. The phylogenetic analysis showed the clustering of Lac1, Lac4 and Lac3 with ascomycete laccases, whereas Lac2 grouped with fungal ferroxidases (together with other hypothetical laccases). Lac3, the main laccase produced by Leptosphaerulina sp. in dye decolorizing and laccase-induced cultures (according to the shotgun analysis of both secretomes) was purified and characterized in this study. It is a sensu-stricto laccase able to decolorize synthetic organic dyes with high efficiency particularly in the presence of natural mediator compounds.

Conclusions

The searching for laccase-type MCOs in ascomycetous families where their presence is poorly known, might provide a source of biocatalysts with potential biotechnological interest and shed light on their role in the fungus. The information provided by the use of genomic and proteomic tools must be combined with the biochemical evaluation of the enzyme to prove its catalytic activity and applicability potential.

Electronic supplementary material

The online version of this article (doi:10.1186/s12896-015-0192-2) contains supplementary material, which is available to authorized users.

The Trametes hirsuta 072 laccase multigene family: Genes identification and transcriptional analysis under copper ions induction

Laccases, blue copper-containing oxidases, ≿ an play an important role in a variety of natural processes. The majority of fungal laccases are encoded by multigene families that express closely related proteins with distinct functions. Currently, only the properties of major gene products of the fungal laccase families have been described. Our study is focused on identification and characterization of laccase genes, which are transcribed in basidiomycete Trametes hirsuta 072, an efficient lignin degrader, in a liquid medium, both without and with induction of laccase transcription by copper ions. We carried out production of cDNA libraries from total fungal RNA, followed by suppression subtractive hybridization and mirror orientation selection procedures, and then used Next Generation Sequencing to identify low abundance and differentially expressed laccase transcripts. This approach resulted in description of five laccase genes of the fungal family, which, according to the phylogenetic analysis, belong to distinct clusters within the Trametes genus. Further analysis established similarity of physical, chemical, and catalytic properties between laccases inside each cluster. Structural modeling suggested importance of the sequence differences in the clusters for laccase substrate specificity and catalytic efficiency. The implications of the laccase variations for the fungal physiology are discussed.

Cloning and functional analysis of a laccase gene during fruiting body formation in Hypsizygus marmoreus

The Hypsizygus marmoreus laccase gene (lcc1) sequence was cloned and analyzed. The genomic DNA of lcc1 is 2336 bp, comprising 13 introns and 14 exons. The 1626-bp full-length cDNA encodes a mature laccase protein containing 542 amino acids, with a 21-amino acid signal peptide. Phylogenetic analysis showed that the lcc1 amino acid sequence is homologous to basidiomycete laccases and shares the highest similarity with Flammulina velutipes laccase. A 2021-bp promoter sequence containing a TATA box, CAAT box, and several putative cis-acting elements was also identified. To study the function of lcc1, we first overexpressed lcc1 in H. marmoreus and found that the transgenic fungus producing recombinant laccase displayed faster mycelial growth than the wild-type (wt) strain. Additionally, primordium initiation was induced 3-5 days earlier in the transgenic fungus, and fruiting body maturation was also promoted approximately five days earlier than in the wt strain. Furthermore, we detected that lcc1 was sustainably overexpressed and that laccase activity was also higher in the transgenic strains compared with the wt strain during development in H. marmoreus. These results indicate that the H. marmoreus lcc1 gene is involved in mycelial growth and fruiting body initiation by increasing laccase activity.