**5. Ligninolytic fungi**

The methods of chemical and physical lignin degradation have several disadvantages, including their high costs and the possibility to produce secondary contamination as mentioned above [12]. In contrast, biological treatment or biodegradation is an attractive option as it involves energy saving and is environmentally friendly [17].

Bioremediation involves the use of living organisms, usually bacteria or fungi, to remove contaminants from soil and water. Thus, there is an intense interest in white rot fungi that has the ability to degrade some extremely persistent or toxic environmental pollutant [18]. Microorganisms have developed sophisticated metabolic and enzymatic systems for the degradation and conversion of lignin in nontoxic monomers, it is believed that white rot fungi are the main tool for the depolymerization of lignin, since they can secrete a collection of peroxidases and ligninolytic laccases that degrade oxidatively lignin to produce small aromatic molecules [4]. The use of fungi for biodegradation has already been investigated for several decades, one of the best studied is *Phanerochaete chrysosporium* [17]. Most of the white rot fungi belong to basidiomycetes and are responsible for the complete mineralization of the woody components including lignin [19]. Other ligninolytic enzyme-producing fungi are species of ascomycetes such as *Trichoderma reesei*. However, in nature, the degradation of lignin during the process of decomposition of the wood is possible mainly by basidiomycetes [20].

A large variety of white rot fungi simultaneously attacks lignin, hemicellulose, and cellulose, while some others only attack mainly lignin. For example, *Ceriporiopsis subvermispora*, *Phlebia* spp., *Physisporinus rivulosus*, and *Dichomitus squalens* selectively attack lignin, since, the purpose of these fungi is to break down the lignin barrier and make cellulose and hemicellulose accessible to these microorganisms [21]. *Trametes versicolor*, *Heterobasidium annosum*, *P. chrysosporium*, and *Irpex lacteus* simultaneously degrade all components of the cell wall [20].

Another fungus belonging to white rot is *Pleurotus ostreatus*, which produces laccase and manganese peroxidase, but does not secrete lignin peroxidase [22]. *Pleurotus ostreatus* expresses multiple laccase genes encoding isoenzymes with different properties, the physiological meaning of this multiplicity being as yet unknown [23].

Experiments carried out with *Myrothecium verrucaria*, a fungus belonging to ascomycetes, showed that this fungus has the ability to secrete enzymes such as lignin peroxidase (LiP), manganese peroxidase (MnP), and laccase (Lac), and has been used as a biological pretreatment to reduce the lignin content in corn stover [24]. Other important enzyme for lignin degradation is the versatile peroxidase (VP), it appears to be produced from different fungus genera as *Pleurotus*, *Bjerkandera*, *Lipista*, *Panus*, and *Trametes* species [18].

Particularly, the degradation of lignin by *Ceriporiopsis subvermispora*, is produced by a mechanism of a single electron-oxidation closely dependent on the action of MnP. During the decomposition of the wood by *C. subvermispora*, it releases a series of unsaturated fatty acids including linoleic acid, which, according to some studies, was found during the first week of culture before lignin degradation. This reaction seems to depend on the presence of unsaturated fatty acids that are peroxidized by MnP generating organoperoxy radicals capable of oxidizing non-phenolic lignin structures. Therefore, it is suggested that *C. cubvermispora* uses the peroxidation reactions of fatty acids initiated by the enzyme MnP to initiate the degradation of lignin in the cell walls of wood [25].

On the other hand, it has been found that *P. chrysosporium*, when producing LiP and MnP, could degrade anthracene and phenanthrene, which are polycyclic

## *The Roll of Different Kind of Fungi to Eliminate Lignin and Organochlorines: A Review DOI: http://dx.doi.org/10.5772/intechopen.105162*

aromatic hydrocarbons (PAHs) evidencing the role of these enzymes to degrade these types of compounds. Anthracene is used in the production of artificial colorants, insecticides, or coating materials and is listed as one of the priority pollutants of the United States Environmental Protection Agency (USEPA) [26]. Furthermore, previous studies, has been found that white rot fungi such as *Phlebia lindtneri* and *Phlebia brevispora* could hydroxylate polychlorinated dibenzo-p-dioxins, 2,7-dichlorodibenzo-p-dioxin, 2,3,7-trichlorodibenzo-p-dioxin, 1,2,8,9-tetrachlorodibenzopyrodioxine, and 1,2,6,7-tetrachlorodibenzo-p-dioxin [13]. It has been shown that hydroxylation of an aromatic ring is important as the first step for degradation of dioxins and hydrocarbons [13]. Recent studies have reported that *Ganoderma lucidum* could break down trichlorethylene and drugs such as ibuprofen and carbamazepine, since this fungus has the potential to produce all three types of ligninolytic enzymes, although enzymatic activities vary between different strains and culture conditions [27]. All these reports, shows the potential of different fungus strains to be used to eliminate, lignin and POPs.
