Vol. 14(1), pp. 52-67, 7 January, 2015 DOI: 10.5897/AJB2014.14249 Article Number: AED32D349437 ISSN 1684-5315 African Journal of Biotechnology Copyright © 2015 Author(s) retain the copyright of this article http://www.academicjournals.org/AJB Review Oyster mushrooms (Pleurotus) are useful for utilizing lignocellulosic biomass E. A. Adebayo1,2* and D. Martínez-Carrera2 1Department of Pure and Applied Biology, Ladoke Akintola University of Technology, P.M.B. 4000, Ogbomoso, Nigeria. 2Biotechnology of Edible, Functional and Medicinal Mushrooms, Colegio de Postgraduados, Apartado Postal 129, Puela 72001, Puebla, Mexico. Received 16 October, 2014; Accepted 12 December, 2014 This review shows the biotechnological potential of oyster mushrooms with lignocellulosic biomass. The bioprocessing of plant byproducts using Pleurotus species provides numerous value-added products, such as basidiocarps, animal feed, enzymes, and other useful materials. The biodegradation and bioconversion of agro wastes (lignin, cellulose and hemicellulose) could have vital implication in cleaning our environment. The bioprocessing of lignin depends on the potent lignocellulolytic enzymes such as phenol oxidases (laccase) or heme peroxidases (lignin peroxidase (LiP), manganese peroxidase (MnP) and versatile peroxidase) produced by the organism. The cellulose-hydrolysing enzymes (that is, cellulases) basically divided into endo-β-1,4-glucanase , exo-β-1,4-glucanase I and II, and β-glucosidase, they attack cellulose to release glucose, a monomers units from the cellobiose, while several enzymes acted on hemicellulose to give D-xylose from xylobiose. These enzymes have been produced by species of Pleurotus from lignocellulose and can also be used in several biotechnological applications, including detoxification, bioconversion, and bioremediation of resistant pollutants. Key words: Oyster mushroom, lignin, cellulose, hemicellulose. INTRODUCTION Lignocellulosic materials are the most promising and they are posing serious environmental pollution feedstock as natural and renewable resource essential to problems (Howard et al., 2003). Accidentally, much of the the functioning of modern industrial societies (Anwer et lignocellulosic biomass is often disposed of by burning or al., 2014). A large amount of such materials as waste by- just lying values without any important used attached to products are being generated through agricultural them. practices mainly from various agro based industries Recently, lignocellulosic biomasses have gained (Pe´rez et al., 2002). increasing research interests and special importance Large amounts of lignocellulosic waste generated because of their renewable nature (Asgher et al., 2013; through forestry and agricultural practices, paper-pulp Ofori-Boateng and Lee, 2013). This has attracted the industries, timber industries and many agro-industries, interest of many researchers in the utilization of lignocel- *Corresponding author. E-mail: [email protected], [email protected]. Tel: +2348038099092, +5212221903846. Author(s) agree that this article remains permanently open access under the terms of the Creative Commons Attribution License 4.0 International License Adebayo and Martínez-Carrera 53 lulosic wastes. Pleurotus are characterized by a white lignocellulosic materials. spore print, attached to the gills, often with an essentric stip, or no stip at all, and they are com- monly known as Oyster mushrooms (Miles and Chang, CHEMICAL COMPOSITIONS OF LIGNOCELLULOSE 1997). Growing oyster mushroom is becoming more popular throughout the world because of their abilities to Lignocellulosic biomass are the most abundant and less grow at a wide range of climate conditions and utilizing utilized biomass, they includes agricultural wastes, various lignocelluloses. In nature, Pleurotus species live forestry residues, grasses and woody materials, which on parts of plants which are generally poor in nutrients are good source of substrates for oyster mushroom and and vitamins. in turn resulted into valuable products. Agricultural For spawn running and fruit body development, lignin lignocellulosic biomass basically consists of 40 to 50% and cellulose materials such as corn cobs, all cereal cellulose, 25 to 30% hemicellulose and 15 to 20% lignin straws, paper, wood shavings, sawdust, nutshells and (Malherbe and Cloete, 2002; Iqbal, et al., 2011; Menon vegetable wastes as well as food industry wastes are and Rao, 2012). Major structural component of plant cell sufficient (Baysal et al., 2003). Species of the genus walls is cellulose, which is responsible for its mechanical Pleurotus (Fr.) P. Kumm known as oyster mushrooms, strength. Hemicelluloses are macromolecules with rank third place in worldwide production of edible mush- repeated polymers of pentoses and hexoses, while lignin rooms after Agaricus bisporus and Lentinula edodes, and contains three aromatic alcohols (coniferyl alcohol, comprises various edible species with medical, sinapyl alcohol and pcoumaryl alcohol) produced through biotechnological and environmental applications (Cohen a biosynthetic process and forms a protective seal et al., 2002). Pleurotus species present high adaptability around the other two components i.e., cellulose and to produce basidiomata within a wide variety of agro- hemicelluloses (Figure 1) (Sanchez, 2009; Menon and industrial lignocellulosic wastes due to their production of Rao, 2012; Anwar et al., 2014). Composition of ligninolytic and hydrolytic enzymes (Mikiashvili et al., lignocellulose is generally depends on its source; whether 2006). it is derived from the hardwood, softwood, or grasses. Agro-residues contain three major structural polymers, Table 1 shows the typical chemical compositions in cellulose, hemicellulose and lignin, which can be easily cellulose, hemicellulose and lignin from various lignocel- utilized or broken down by the lignocellulotic enzymes. lulosic materials. The variation in chemical compositions Pleurotus species are the most efficient lignin-degrading may be due to the genetic variability among different organisms, with the ability to produce mainly laccases sources (Iqbal et al., 2011; Menon and Rao, 2012: Kumar (EC 1.10.3.2), lignin peroxidase (EC 1.11. 10.14) and et al., 2009; Malherbe and Cloete, 2002). The chemical manganese peroxidase (EC1.11.1.13) (Adebayo et al., formula of cellulose is (C6H10O5)n, with structure of single 2012a). These enzymes present a non-specific biocata- chain polymer shown in Figure 1. lyst mechanism and have been used for bioremediation Cellulose is a highly stable polymer consisting of process due to their ability to degrade azo, heterocyclic, glucose and attached with linear chains up to 12,000 reactive and polymeric dyes (Baldrian and Snajdr, 2006; residues. It is majorly com-posed of (1,4)-D- Forgacs et al., 2004). White-rot basidiomycetes are glucopyranose units, which are attached by β-1,4 among the most potent organisms to biodegrade and linkages with an average molecular weight of around detoxify a wide range of wastes and pollutants. These 100,000 (Himmel et al., 2007). Cellulose held together by fungi selectively attack lignin and related compounds by intermolecular hydro-gen bonds in native state, but they producing one or more of phenol-targeting redox have a strong tendency to form intra-molecular and enzymes, namely the peroxidases and laccases/phenol- intermolecular hydrogen bonds and this tendency oxidases (Ntougias et al., 2012). Prospection for fungi is increases the rigidity of cellulose and makes it highly the ability to secret high levels of lignin-degrading insoluble and highly resistant to most organic solvents. enzymes and novel enzyme variants, with desirable Naturally, cellulose molecules exist as bundles which properties for biotechnological applications (Adebayo et aggregated together in the form of micro-fibrils order that al., 2012a). Therefore, the huge amounts of lignocel- is, crystalline and amorphous regions (Iqbal et al., 2011; lulosic biomass can be potentially bioconverted into Taherzadeh and Karimi, 2008). different high value raw materials and products such as Hemicellulose mainly consists of glucuronoxylan, bio-ethanol, enriched animal feed, cheap energy sources glucomannan and trace amounts of other polysaccha- for microbial cultivation (mushrooms included) and rides. They are majorly found in grasses and straws enzyme production, biodegradation and bioremediation of contain arabinan, galactan and xylan, while mannan is a toxic organic compounds (Koutrotsios et al., 2014; Anwar component of hardwood and softwood (Brigham et al., et al., 2014; Asgher et al., 2013; Irshad et al., 2013; 1996). Hemicelluloses have sugar backbone which Ntougias et al., 2012). The objectives of this review are composed xylans, mannans and glucans, with xylans and the compilation of the newer achievements in the mannans being the most common (Wyman et al., 2005). technologies developed between oyster mushrooms and Galactans, arabinans and arabinogalactans are also 54 Afr. J. Biotechnol. Figure 1. Diagrammatic illustration of the framework of lignocellulose; lignin, cellulose and hemicellulose. included in the hemicellulose group; however, they do not xylospyranose is the backbone of the polymer and share the equatorial β-1,4 linked backbone structure. In connected with β-1,4 linkages. Hemicellulose has hardwoods, glucuronoxylan (O-acetyl-4-O-methyl- average molecular weight of <30,000. Cellulose and glucurono-b-Dxylan) is the predominant component, hemicellulose