# Lacase in Biorefinery of Lignocellulosic Biomass
## 2 Pretreatment of Lignocellulosic Biomasses
### Biological Pretreatment for Lignocellulosic Biomasses  
Biological pretreatment methods have gained attention in recent years as an eco-friendly and sustainable solution for waste management and environmental remediation. In this pretreatment method, primarily, lignin is depolymerized and in turn increases biomass accessibility to enzymes. During this process inhibitory compounds are not released being biological in nature, causing easy downstream processing. It involves the use of microorganisms, such as fungi and bacteria, or even free enzymes, such as lactose, to break down complex lignocellulosic compounds into simpler forms. This process enhances the biodegradability of the waste and reduces the time required for biodegradation. However, here we will discuss the fungi-, bacteria-, and enzyme-based biological pretreatment [29]. Microorganisms such as bacteria and fungi have been used for biological pretreatments of lignocellulosic biomasses. These microorganisms secrete ligninolytic enzymes that can break down lignin into smaller fragments. The most used microorganisms for this purpose are white-rot fungi, such as _Phanerochaete chrysosporium_ and _Pleutotus ostreatus_[6; 30]. Fungi can break down lignin into its constituent monomers, making it more accessible. The most commonly used fungi for lignin depolymerization are white-rot fungi, which secrete ligninolytic enzymes, such as laccase, manganese peroxidase, and lignin peroxidase [31]. Bacteria are also used for the biological pretreatment of lignocellulosic biomasses. Some bacteria secrete ligninolytic enzymes, while others can utilize lignin as a carbon source. Some common bacteria for this purpose are _Streptomyces_ sp. and _Bacillus_ sp. [32]. The major disadvantage is that it is quite slow; hence, it takes days and weeks to get biomasses pretreated by this process. It can also be done using enzymes directly rather than microorganisms. The common enzymes used for biological pretreatment are laccases, manganese peroxididases, and lignin peroxididases [33]. This is comparatively faster than the earlier one, where microorganisms are employed rather than the enzymes directly. These enzymes are mostly produced by filamentous fungi.  
Most biological pretreatment methods utilize the ligninolytic enzyme system, which consists of oxidoreductaseuates that can break down lignin, thereby enhancing the biomass degradation. The system comprises laccases and peroxididases that possess a high redox potential and can oxidize the lignin polymer either directly or via mediators, i.e., low molecular-weight organic compounds capable of attacking the lignin structure by diffusing into the cell wall pores [34]. Biological pretreatment can be carried out using microorganisms that secrete ligninolytic enzymes or the enzymes themselves to disrupt part of the lignin and its structure, thus enabling hydrolytic enzymes used in the biorefinery process to access holocellulose and release sugars [35]. Besides improving feedstock enzymatic digestibility, biological pretreatments have other potential biorefinery applications. The produced enzymes can be extracted and used in other processes, and the pretreatment may yield coproducts, including lignin derivatives and organic compounds that act as platform chemicals and enhance the process value [35]. Converting the nonfermentable constituents of lignocellulosic biomasses into value-added products is a crucial missing link for the biorefinery success [36]. Generally, ligninolytic microorganisms and enzyme extracts can serve as biocatalysts for many reactions aimed at producing biofuels and bioproducts within biorefinery.