Abstract
The properties and capacities of the ligninolytic enzymes of Daedaleopsis spp. are still unknown. This is the first study on the effect of plant residues and period of cultivation on the properties of Mn-oxidizing peroxidases and laccases of D. confragosa and D. tricolor, as well as their ligninolytic potentials. Wheat straw was the optimal carbon source for synthesis of highly active Mn-dependent peroxidases (4126.9 U/L in D. confragosa and 2037.9 U/L in D. tricolor). However, laccases were the predominant enzymes, and the best inducer of their activity (up 16000.0 U/L) was cherry sawdust. Wheat straw was the most susceptible plant residue to the effect of the enzymes, and extent of lignin degradation was 43.3% after 14 days of fermentation with D. tricolor. However, D. confragosa was a more effective lignin degrader, as it converted even 21.3% wheat straw lignin on the 6th day of cultivation. The results of the study clearly showed that delignification extent depends on mushroom species and on the type of plant residue, which is extremely important for potential use in biotechnological processes.
Download PDF
Full Article
Lignocellulose Degradation by Daedaleopsis confragosa and D. tricolor
Mirjana Stajić,a,* Jasmina Ćilerdžić,a Milica Galić,a Žarko Ivanović,b and Jelena Vukojević a
The properties and capacities of the ligninolytic enzymes of Daedaleopsis spp. are still unknown. This is the first study on the effect of plant residues and period of cultivation on the properties of Mn-oxidizing peroxidases and laccases of D. confragosa and D. tricolor, as well as their ligninolytic potentials. Wheat straw was the optimal carbon source for synthesis of highly active Mn-dependent peroxidases (4126.9 U/L in D. confragosa and 2037.9 U/L in D. tricolor). However, laccases were the predominant enzymes, and the best inducer of their activity (up 16000.0 U/L) was cherry sawdust. Wheat straw was the most susceptible plant residue to the effect of the enzymes, and extent of lignin degradation was 43.3% after 14 days of fermentation with D. tricolor. However, D. confragosa was a more effective lignin degrader, as it converted even 21.3% wheat straw lignin on the 6th day of cultivation. The results of the study clearly showed that delignification extent depends on mushroom species and on the type of plant residue, which is extremely important for potential use in biotechnological processes.
Keywords: Daedaleopsis spp; Delignification; Ligninolytic enzymes; Lignocellulosic residues; Solid-state fermentation
Contact information: a: University of Belgrade, Faculty of Biology, Takovska 43, 11000 Belgrade, Serbia; b: Institute for Plant Protection and Environment; Teodora Drajzera 9; 11000 Belgrade; Serbia;
* Corresponding author: stajicm@bio.bg.ac.rs
INTRODUCTION
A large amount of lignocellulosic residue is produced annually worldwide (150 billion tons), and the dominant biomass differs depending on the region (Asim et al. 2015; Gupta and Verma 2015). Production of these wastes is also remarkable in Serbia, where 51% of the territory contains agricultural crops and about 27% is forest (Jordanović-Vasić 2009). Adding the biomass of weeds, municipal, and food industry wastes to the quantity of agro-forestry residues, the combination represents an enormous amount of the wastes, which present serious ballast for the environment due to inadequate management, i.e., deposition and usage. However, lignocellulosic materials could be important resources for food, feed, paper, chemicals, and energy production (Stajić et al. 2016). These biotechnological processes require pretreatment of the biomass. The treatment can be physical, chemical, physico-chemical, or biological, which is recently preferred due to significant delignification selectivity, minimal release of toxic by-products, and lower energy consumption (Sánchez 2009). White rot fungi play the main role in the biological biomass pretreatment; they synthesize ligninolytic enzymes, i.e., lignin- and Mn-oxidizing peroxidases, laccases, and some auxiliary enzymes (Stajić et al. 2016). Because mushrooms have different levels of production of active ligninolytic enzymes, they have different potential in the various biotechnological processes. Thus, there have been recent studies of the enzyme properties and optimization of cultivation conditions for their synthesis and maximal delignification.
Species of the genus Daedaleopsis are insufficiently studied, even though they are known as white rot fungi (Marković 2012). D. confragosa (Bolton) J. Schröt and D. tricolor (Bull.) Bondavtsev & Singer are the most commonly researched species of the genus, especially with regard to their problematic taxonomy and medicinal potential (Rösecke and König 2000; Bernicchia et al. 2006). Although these species naturally occur as biotrophs or necrotrophs in numerous broadleaf species, some properties of their enzyme systems are not sufficiently clarified. Therefore, this study evaluated D. confragosa and D. tricolor for their potential to delignify their natural substrates—cherry and beech sawdust—and wheat straw, an alternative substrate.
Materials
Fruiting bodies collected on Avala mountain (Serbia) and in Veliko Tarnovo (Bulgaria) were morphologically identified as Daedaleopsis confragosa and D. tricolor, respectively. The cultures were isolated from collected fruiting bodies and maintained on malt agar medium in culture collection of Institute of Botany, Faculty of Biology, University of Belgrade (BEOFB).
Methods
Cultivation conditions
Inoculum was prepared as described previously (Stajić et al. 2010). Briefly, synthetic medium (glucose, 10.0 g/L; NH4NO3, 2.0 g/L; K2HPO4, 1.0 g/L; NaH2PO4 × H2O, 0.4 g/L; MgSO4 × 7H2O, 0.5 g/L; yeast extract, 2.0 g/L; pH 6.5) was inoculated with mycelial discs from 7-day old cultures grown on malt agar. Cultures were incubated at room temperature (22 ± 2 °C) on a rotary shaker (100 rpm) prior to washing and homogenization of the obtained biomass. Wheat straw, beech sawdust, and cherry sawdust fermentation were conducted under solid-state conditions for 6, 10, 14, 18, 22, and 26 days. Experiments were carried out in triplicate; results are expressed as mean ± standard error.
Assays of enzyme activity and total protein production
The ligninolytic enzymes were extracted by sample mixing with 50.0 mL of distilled water (dH2O) by a magnetic stirrer (4 °C, 10 min). The obtained extracts were separated from plant residues and mycelial rests by centrifugation (3000 rpm, 4 °C, 10 min). The supernatants were used to measure the activity of Mn-oxidizing peroxidases and laccases, and the total protein content was measured with a spectrophotometer (BioQuest CECIL CE2501, Cambridge, UK). Phenol red (ε610 = 22,000 M-1 cm-1) was used as substrate for defining activities of Mn-oxidizing peroxidases [Mn-dependent peroxidase (MnP, EC 1.11.1.13) and Mn-independent peroxidase (MnIP, EC 1.11.1.16)], and 2,2‘-azino-bis-[3-ethylthiazoline-6-sulfonate] (ABTS) (ε436 = 29,300 M-1 cm-1) for laccase activity monitoring (Stajić et al. 2010). The reaction mixture (Vtot = 1.0 mL) for measurement of laccases contained buffer, ABTS, and sample while the peroxidases one were composed of buffer, sample, 2.0 mM H2O2, phenol red, with or without 2.0 mM MnSO4 (for MnP and MnIP, respectively). An enzymatic activity of 1 U was defined as the amount of enzyme that transformed 1.0 μmol of substrate per minute.
The total protein content of (mg/mL) was determined in a spectrophotometer (λ = 595 nm) in a reaction mixture of Coomassie brilliant blue G-250, using standard curve obtained from solutions of bovine serum albumin (0.00, 0.01, 0.02, 0.03, 0.05 0.1, 0.2, 0.3, 0.5, 0.8, and 1.0 mg/mL) and Bradford reagent (Silva et al. 2005).
Electrophoresis
The profiles of Mn-oxidizing peroxidases and laccases of D. confragosa BEOFB 710 and D. tricolor BEOFB 720 were screened under cultivation conditions where all tested enzymes showed significant activities. A Mini IEF Cell-Model 111 (BIO-RAD, Hercules, CA, USA) was used for isoelectric focusing (IEF) and defining the isoelectric points (pI) of enzyme isoforms. IEF was carried out in 7.5% polyacrylamide gel with 5.0% ampholyte on a pH gradient from 3.0 to 10.0 using an IEF marker (pI range from 3.6 to 9.3; Sigma-Aldrich, St. Louis, MO, USA) (Ćilerdžić et al. 2016). According to this method, bands with Mn-oxidizing peroxidases activities were located via incubation of the gel in 4-Cl-1-naphtol/H2O2/potassium phosphate buffer mixture (with or without MnSO4 for MnP and MnIP, respectively) at room temperature (22 2 °C) until the appearance of dark-brown bands. Laccase bands were located by gel incubation in ABTS/phosphate buffer. After focusing, the gel was fixed in 12.0% trichloroacetic acid, and protein bands were detected by staining with the solution of 0.1% CBB R in fixative (methanol, acetic acid, and H2O in a 45:10:45 ratio).
Determination of hemicellulose, cellulose, and lignin contents
The amount of lignin, hemicellulose, and cellulose in the selected plant raw materials was defined before and after D. confragosa and D. tricolor cultivation. Hemicellulose content was determined by the method of Van Soest et al. (1991). To remove soluble sugars, proteins, pectin, lipids, and vitamins, a dried ground sample of 1.0 g was treated with a solution of neutral detergent and Na2SO3 under refluxing conditions, and the obtained biomass presented neutral detergent fibers (NDF). Hemicellulose was removed with a solution of acidic detergent under refluxing conditions, and the content of acidic detergent fibers (ADF) was measured. The hemicellulose content in the tested sample was calculated as the difference between ADF and NDF.
Acidic detergent fibers were used to determine the cellulose and lignin contents. Lignin content (LC) was defined by the Klason method (Kirk and Obst 1988), by incubation of sample in 72% H2SO4 at 30 °C and its hydrolysis at 120 °C. Lignin content was expressed as a percentage of that present in the original sample, while the cellulose content was calculated as ADF minus LC.
RESULTS AND DISCUSSION
Enzyme Properties Depending on Plant Raw Materials and Cultivation Period
Both Daedaleopsis species produced enzymes, but their activities varied remarkably depending on the carbon sources, i.e., plant residue and cultivation period (Fig. 1). Wheat straw was the best carbon source for maximizing MnP activity. However, the activity depended on the cultivation period. Thus, the highest MnP activity was noted on day 14 of wheat straw fermentation by D. confragosa and D. tricolor (4126.9 U/L and 2037.9 U/L, respectively); activity decreased with prolonged cultivation to day 26 (Fig. 1). Compared with MnP, MnIP was less active, with the maximum on day 10 of wheat straw fermentation by both species (674.2 U/L vs. 635.1 U/L). The activity decreased gradually over the cultivation period, with almost no activity reported on day 26 (Fig. 1).
Fig. 1. Effect of plant residues and cultivation period on the activities of Mn-dependent peroxidase (white bar), Mn-independent peroxidase (gray bar), and laccase (–) in Daedaleopsis confragosa (A) and D. tricolor (B). Data represent mean value of activities of three different samples. Variations are given as standard errors.
The optimal carbon source for laccase activity in both species was cherry sawdust, and the maximal activities, up 16000.0 U/L, were noted on day 6 of fermentation. However, the values were also remarkable on day 10 and 14 and thereafter declined to the minimum of 949.9 U/L on day 26. Beech sawdust and wheat straw slightly stimulated the enzyme activity only on day 6 and 10 (Fig. 1). Generally, the laccase activity was significantly higher than the Mn-oxidizing peroxidase activity.
The type of plant residue and cultivation period also affected protein production and specific enzyme activities. The maximal value of specific MnP activity was noted on day 22 of cherry sawdust fermentation by D. tricolor (4.6 U/mg), while the maximums of MnIP (6.1 U/mg) and laccase (6.3 U/mg) were found in wheat straw fermentation by D. confragosa on day 18 and D. tricolor on day 10, respectively.
Because all tested enzymes showed remarkable high activity after 10 days of fermentation, the isoenzyme profiles were monitored at that point. The IEF profiles of Mn-oxidizing peroxidases and laccase isoforms showed variations in different plant residues. Their pI values ranged between 3.6 and 6.8, as visualized on zymograms (Fig. 2).
Fig. 2. Isoelectric focusing pattern of Mn-dependent peroxidases (A), Mn-independent peroxidases (B), and laccases (C) in Daedaleopsis confragosa and D. tricolor after 10-day fermentation of cherry sawdust (1), beech sawdust (2) and wheat straw (3)
In cultivation on cherry sawdust, both species produced two MnP isoenzymes of pI of about 4.6 and 5.9, while D. tricolor synthesized one more with a pI of 3.8. Beech sawdust induced production of only one MnP isoform (pI 5.1) in D. confragosa, while no isoform was detected after wheat straw fermentation by this species (Fig. 2A). The cherry sawdust was also the best inducer of MnIP isoforms (Fig. 2B). Namely, five bands at pIs 3.7, 3.8, 5.1, 5.9, and 6.6 were observed in zymograms of D. confragosa, while only two isoforms at pIs 3.7 and 4.6 were detected in D. tricolor. Likewise, beech sawdust stimulated MnIP synthesis in D. confragosa; several isoforms ranged from pI 3.6 to 6.8. Wheat straw was a better carbon source for the isoenzyme synthesis by D. tricolor (pI 3.6, 3.8, and 4.6) (Fig. 2B).
Both species produced only a few laccase isoforms during cultivation in all tested plant residues (Fig. 2C). D. confragosa synthesized two isoenzymes (pIs 3.6 and 5.9) during wheat straw fermentation and only one (pI 3.6) in cherry sawdust fermentation. No isoform was visualized after beech sawdust fermentation, which was different from D. tricolor zymograms. Namely, two bends were detected after D. tricolor cultivation on cherry sawdust (pI 3.8 and 5.1) and one on beech sawdust (pI 5.1) and wheat straw (pI 3.6) (Fig. 2C).
Effect of Cultivation Conditions on Lignocellulose Degradation
The lignin, hemicellulose, and cellulose contents in the plant raw materials were different (Table 1). The extent of the polymer degradation increased during fermentation, but the rate of degradation depended on species and plant residue. However, in some cases, the depolymerization degree did not have a positive correlation with the level of enzyme activity. The tested Daedaleopsis species were highly effective delignificators of wheat straw, which was the most susceptible plant residue. After 14 days of D. confragosa and D. tricolor cultivation, 43.3% and 42.4% of lignin, respectively, was degraded.
Table 1. Daedaleopsis confragosa and D. tricolor to Degradation of Lignocellulosic Polymers
The extent of cherry sawdust lignin depolymerization increased with the period of fermentation in both species, but D. tricolor was more of a potential degrader. Although both species mineralized almost identical amounts of beech sawdust lignin after 14 days of fermentation, D. confragosa showed more rapid degradation than D. tricolor, with 22.8% vs. 2.1% delignification, respectively, on day 6 (Table 1). Daedaleopsis species were better hemicellulose than cellulose mineralizators, especially D. confragosa that degraded even 30.3% of wheat straw hemicellulose after 14-day old fermentation. D. tricolor was a better degrader of cellulose, particularly after 10 days of cherry sawdust fermentation (17.3%) (Table 1). Generally, D. confragosa was a better degrader of wheat straw and beech sawdust polymers, while a higher extent of cherry sawdust depolymerization was obtained with D. tricolor.
Although studies of fungal ligninolytic enzymes are current, because of their wide biotechnological potential, data on properties and capacities of the Daedaleopsis spp. enzymes have remained unknown until this work. Information about the abilities of D. confragosa and D. tricolor to do ligninolysis and thus participate in transformation of lignocellulose residues to feed, paper, and energy can be considered as the main contribution of this study.
Fungal species/strains and nature of lignocellulose substrate are important factors that determine the expression and delignification activity of ligninolytic enzymes (Camarero et al. 1996; Elisashvili et al. 2008; Simonić et al. 2010; Arora et al. 2011; Knežević et al. 2013; Ćilerdžić et al. 2016). There are significant differences in ligninolytic enzyme characteristics and ligninolysis capacity between the two species studied here; these differences are explained by their phylogeny and genetics. Camarero et al. (1996) reported interspecific diversity in MnP activity between Coriolus hirsutus and C. pubescens as well as between Pleurotus salignus and P. ostreatus, while intraspecific variabilities of laccase and Mn-oxidizing peroxidases activities were noted in Ganoderma lucidum by Simonić et al. (2010). Long-term studies also demonstrated the dependence of these enzymes’ properties on plant residue composition, especially the proportion of lignin in relation to hemicellulose and cellulose (D’Souza et al. 1999; Fenice et al. 2003; Songulashvili et al. 2006; Ćilerdžić et al. 2011). Songulashvili et al. (2006) found that substrate type was essential for MnP production and activity in Phanerochaete chrysosporium and Phellinus robustus, and Ćilerdžić et al. (2011) showed that Trametes hirsuta synthesized the most active form of this enzyme during wheat straw fermentation, which was in accordance with data obtained for the studied Daedaleopsis species. However, activities and isoform profiles of the enzymes also depend on cultivation period due to their various metabolism (Gómez-Toribio et al. 2001). Namely, in D. confragosa and D. tricolor, laccases were the most active enzymes on day 6 of fermentation in all studied plant raw materials, but the highest delignification was reached on day 14 due to extraordinarily active MnPs, which attack the lignin and make it accessible for penetration by laccases.
The obtained results confirmed those of Knežević et al. (2013), which demonstrated differences among species in delignification ability as well as an absence of correlation with enzyme activity. Although the peak enzyme activities were reached during the early substrate colonization phase, a remarkable amount of lignin depolymerization was measured in the later phase. This result reflects that the earlier phase is associated with cell wall opening and the release of active compounds, such as reactive oxygen species, that are involved in enzyme activation and initiation of delignification; extensive lignin degradation is linked to extracellular polysaccharides (Valmaseda et al. 1991; Hammel et al. 2002). This difference in delignification can be explained by differences in lignin composition, its ratio to hemicellulose and cellulose, as well as cell wall structural organization between grasses and wood (Li et al. 2012). Thus, Fukasawa et al. (2005) showed that D. tricolor strain cultivated on Fagus crenata removed 42.1% lignin and simultaneously mineralized 49.8% carbohydrates, while Asgher et al. (2016) reported an extremely high level of wheat straw delignification by Schizophyllum commune (72.3%).
CONCLUSIONS
- The properties of Mn-oxidizing peroxidases and laccase from D. confragosa and D. tricolor strains are greatly affected by the substrate type and composition and the cultivation period.
- Laccases were the predominant enzymes.
- Cherry sawdust was the optimal carbon source for synthesis of highly active laccases.
- Wheat straw was the most susceptible plant residue to Daedaleopsis spp. enzymes.
- D. confragosa was more effective lignin degrader than D. tricolor.
ACKNOWLEDGEMENTS
This study was carried out under Project No. 173032, which is financially supported by the Ministry of Education, Science and Technological Development of the Republic of Serbia.
REFERENCES CITED
Arora, D. S., Sharma, R. K., and Chandra, P. (2011). “Biodelignification of wheat straw and its effect on in vitro digestibility and antioxidant properties,” International Biodeterioration and Biodegradation 65(2), 352-358. DOI: 10.1016/j.ibiod.2010.12.009
Asim, N., Emdadi, Z., Mohammad, M., Yarmo, M. A., and Sopian, K. (2015). “Agricultural solid wastes for green desiccant applications: An overview of research achievements, opportunities and perspectives,” Journal of Cleaner Production 91, 26-35. DOI: 10.1016/j.jclepro.2014.12.015
Asgher, M., Wahab, A., Bilal, M., and Iqbal, H. M. N. (2016). “Lignocellulose degradation and production of lignin modifying enzymes by Schizophyllum commune IBL-06 in solid-state fermentation,” Biocatalysis and Agricultural Biotechnology 6, 195-201. DOI: 10.1016/j.bcab.2016.04.003
Bernicchia, A., Fugazzola, M. A., Gemelli, V., Mantovani, B., Lucchetti, A., Cesari, M., and Speroni, E. (2006). “DNA recovered and sequenced from an almost 7000 y-old Neolithic polypore, Daedaleopsis tricolor,” Mycological Research 110(1), 14-17. DOI: 10.1016/j.mycres.2005.09.012
Camarero, S., Böckle, B., Martínez, M. J., and Martínez, A. T. (1996). “Manganeze mediated lignin degradation by Pleurotus pulmonarius,” Applied and Environmental Microbiology62(3), 1070-1072. ISSN: 0099-2240
Ćilerdžić, J., Stajić, M., Vukojević, J., Duletić-Laušević, S., and Knežević, A., (2011). “Potential of Trametes hirsuta to produce ligninolytic enzymes during degradation of agricultural residues,” BioResources 6(3), 2885-2895. DOI: 10.15376/biores.7.4.2885-2895
Ćilerdžić, J., Stajić, M., and Vukojević, J. (2016). “Degradation of wheat straw and oak sawdust by Ganoderma applanatum,” International Biodeterioration and Biodegradation 114, 39-44. DOI: 10.1016/j.ibiod.2016.05.024
D`Souza, T. M., Merritt, C. S., and Reddy, C. A. (1999). “Lignin-modifying enzymes of the white rot basidiomycete Ganoderma lucidum,” Applied and Environmantal Microbiology65(12), 5307-5313. ISSN: 0099-2240
Elisashvili, V., Penninckx, M., Kachiishvili, E., Tsiklauri, N., Metreveli, E., Kharziani, T., and Kvesitadze, G. (2008). “Lentinus edodes and Pleurotus species lignocellulolytic enzymes activity in submerged and solid state fermentation of lignocellulosic wastes of different composition,” Bioresource Technology 99(3), 457-462. DOI: 10.1016/j.biortech.2007.01.011
Fenice, M., Sermanni, G. G., Federici, F., and D`Annibale, A. (2003). “Submerged and solid-state production of laccase and Mn-peroxidase by Panus tigrinus on olive mill wastewater-based media,” Journal of Biotechnology 100(1), 77-85. DOI: 10.1016/S0168-1656(02)00241-9
Fukasawa, Y., Osono, T., and Takeda, H. (2005). “Decomposition of Japanese beech wood by diverse fungi isolated from cool temperate deciduous forest,” Mycoscience 46(2), 97-101. DOI: 10.1007/S10267-004-0215-7
Gómez-Toribio, V., Martínez, A. T., Martínez, M. J., and Guillén, F. (2001). “Oxidation of hydroquinones by the versatile ligninolytic peroxidase from Pleurotus eryngii. H2O2generation and the influence of Mn2+,” European Journal of Biochemistry 268(17), 4787-4793. DOI: 10.1046/j.1432-1327.2001.02405.x
Gupta, A., and Verma, J. P. (2015). “Sustainable bio-ethanol production from agro-residues: A review,” Renewable and Sustainable Energy Reviews 41, 550-567. DOI:
10.1016/j.rser.2014.08.032
Hammel, K. E., Kapich, A. N., Jensen, K. A., and Ryan, Z. C. (2002). “Reactive oxygen species as agents of wood decay by fungi,” Enzyme and Microbial Technology 30(4), 445-453. DOI: 10.1016/S0141-0229(02)00011-X
Jordanović-Vasić, M. (2009). “Upotreba biomase iz poljoprivrednog otpada kao obnovljivog izvora energije,” Nauka+Praksa 12(1), 60-63. ISSN: 1451-8341
Kirk, T. K., and Obst, J. R. (1988). “Lignin determination,” in: Methods in Enzymology, S. P. Colowick and N. O. Kaplan (eds.), Academic Press, San Diego, CA, pp. 87-101.
Knežević, A., Milovanović, I., Stajić, M., Lončar, N., Brčeski, I., Vukojević, J., and Ćilerdžić, J. (2013). “Lignin degradation by selected fungal species,” Bioresource Technology 138, 117-123. DOI: 10.1016/j.biortech.2013.03.182
Li, M., Foster, C., Kelkar, S., Pu, Y., Holmes, D., Ragauskas, A., Saffron, C. M., and Hodge, D. B. (2012). “Structural characterization of alkaline hydrogen peroxide pretreated grasses exhibiting diverse lignin phenotypes,” Biotechnology for Biofuels 5(38), 1-15. DOI: 10.1186/1754-6834-5-38
Marković, M. P. (2012). Investigation of Parasitic Fungi on Wild Cherry (Prunus avium L.) with Special Accent on Bioecology of Daedaleopsis confragosa (Bilt.: Fr.) J. Schroet, Ph.D. Dissertation, University of Belgrade, Belgrade, Serbia.
Rösecke, J., and König, W. A. (2000). “Constituents of the fungi Daedalea quercina and Daedaleopsis confragosa var. tricolor,” Phytochemistry 54(8), 757-762. DOI:
10.1016/S0031-9422(00)00130-8
Sánchez, C. (2009). “Lignocellulosic residues: Biodegradation and bioconversion by fungi,” Biotechnology Advances 27(2), 185-194. DOI: 10.1016/j.biotechadv.2008.11.001
Silva, C. M. M. S., Soares de Melo, I., and Roberto de Oliveira, P. (2005). “Ligninolytic enzyme production by Ganoderma spp,” Enzyme and Microbial Technology 37(3), 324-329. DOI: 10.1016/j.enzmictec.2004.12.007
Simonić, J., Vukojević, J., Stajić, M., and Glamočlija, J. (2010). “Intraspecific diversity within Ganoderma lucidum in the production of laccase and Mn-dependent peroxidases during plant residues fermentation,” Applied Biochemistry and Biotechnology 162(2), 408-415. DOI: 10.1007/s12010-009-8833-3
Songulashvili, G., Elisashvili, V., Wasser, S. P., Nevo, E., and Hadar, Y. (2006). “Laccase and manganese peroxidase activities of Phellinus robustus and Ganoderma adspersum grown on food industry wastes in submerged fermentation,” Biotechnology Letters 28(18), 1425-1429. DOI: 10.1007/s10529-006-9109-4
Stajić, M., Kukavica, B., Vukojević, J., Simonić, J., Veljović-Jovanović, S., and Duletić-Laušević, S. (2010). “Wheat straw conversion by enzymatic system of Ganoderma lucidum,” BioResources 5(4), 2362-2373. DOI: 10.15376/biores.5.4.2362-2373
Stajić, M., Vukojević, J., Milovanović, I., Ćilerdžić, J., and Knežević, A. (2016). “Role of mushroom Mn-oxidizing peroxidases in biomass conversion,” in: Microbial Enzymes in Bioconversion of Biomass, V. K. Gupta (ed.), Springer-Verlag, New York, NY, pp. 251-269.
Valmaseda, M., Martínez, M. J., and Martínez, A. T. (1991). “Kinetics of wheat straw solid-state fermentation with Trametes versicolor and Pleurotus ostreatus – Lignin and polysaccharide alteration and production of related enzyme activities,” Applied Microbiology and Biotechnology 35(6), 817-823. DOI: 10.1007/BF00169902
Van Soest, P. J., Robertson, J. B., and Lewis, B. A. (1991). “Methods for dietary fiber, neutral detergent fiber, and non-starch polysaccharides in relation to animal nutrition,” Journal of Dairy Science 74(10), 3583-3597. DOI: 10.3168/jds.S0022-0302(91)78551-2
Article submitted: May 4, 2017; Peer review completed: July 8, 2017; Revised version received: July 27, 2017; Accepted: August 5, 2017; Published: August 16, 2017.
DOI: 10.15376/biores.12.4.7195-7204