Bioconversion of lignocellulosic biomass: biochemical and molecular perspectives

Abstract

In view of rising prices of crude oil due to increasing fuel demands, the need for alternative sources of bioenergy is expected to increase sharply in the coming years. Among potential alternative bioenergy resources, lignocellulosics have been identified as the prime source of biofuels and other value-added products. Lignocelluloses as agricultural, industrial and forest residuals account for the majority of the total biomass present in the world. To initiate the production of industrially important products from cellulosic biomass, bioconversion of the cellulosic components into fermentable sugars is necessary. A variety of microorganisms including bacteria and fungi may have the ability to degrade the cellulosic biomass to glucose monomers. Bacterial cellulases exist as discrete multi-enzyme complexes, called cellulosomes that consist of multiple subunits. Cellulolytic enzyme systems from the filamentous fungi, especially Trichoderma reesei, contain two exoglucanases or cellobiohydrolases (CBH1 and CBH2), at least four endoglucanases (EG1, EG2, EG3, EG5), and one beta-glucosidase. These enzymes act synergistically to catalyse the hydrolysis of cellulose. Different physical parameters such as pH, temperature, adsorption, chemical factors like nitrogen, phosphorus, presence of phenolic compounds and other inhibitors can critically influence the bioconversion of lignocellulose. The production of cellulases by microbial cells is governed by genetic and biochemical controls including induction, catabolite repression, or end product inhibition. Several efforts have been made to increase the production of cellulases through strain improvement by mutagenesis. Various physical and chemical methods have been used to develop bacterial and fungal strains producing higher amounts of cellulase, all with limited success. Cellulosic bioconversion is a complex process and requires the synergistic action of the three enzymatic components consisting of endoglucanases, exoglucanases and beta-glucosidases. The co-cultivation of microbes in fermentation can increase the quantity of the desirable components of the cellulase complex. An understanding of the molecular mechanism leading to biodegradation of lignocelluloses and the development of the bioprocessing potential of cellulolytic microorganisms might effectively be accomplished with recombinant DNA technology. For instance, cloning and sequencing of the various cellulolytic genes could economize the cellulase production process. Apart from that, metabolic engineering and genomics approaches have great potential for enhancing our understanding of the molecular mechanism of bioconversion of lignocelluloses to value added economically significant products in the future.

Characterization and Influence of a Multi-enzymatic Biopreparation for Biogas Yield Enhancement

“…The biopreparation did not differ in terms of nonspecific cellulolytic activity from commercially available enzyme preparations, which could potentially be used for organic biomass pretreatment prior to anaerobic bioconversion. Kowalska-Wentel (2015) or Pectinex Ultra SP-L (Novozyme, Bagsvaerd, Denmark β-galactosidase activity immobilized onto Eupergit C) from Aspergillus aculeatus (Aslan and Tanrıseven, 2007). The enzyme mixture was characterized by the presence of other enzymes with relatively wider range and high activity, which is its advantage over others biopreparations mentioned above.…”

Characteristics of a microbial consortium with high lignocelluloses-decomposing capacity

“…Total weight loss of rice straw included the degradation of cellulosic materials and non-cellulosic materials. In plant tissue, in addition to cellulose, hemicellulose, lignin, there are a lot of other material such as ash, pectin, protein and other components which occupy a considerable proportion (about 30%) [2]. Figure.2 showed that there was still about 30% undegraded material in rice straw at the end of the fermentation; main ingredient was 80% ash, which is hard to biotransformation but can be effectively utilized.…”

“…With the depletion of non-renewable energy, as the most attractive and promising avenue for cost-efficient treatment, bioconversion of large amounts of lignocellulosic biomass into fermentable material has been considered to be potential application in the area of bioenergy generation [2]. Therefore, enormous research efforts have been invested on bioconversion of lignocellulosic biomass in decades [3,4].…”

Kloning gen penyandi β-1,6-glukanase kapang secara cepat dengan teknik RT-PCR menggunakan primer spesifik Rapid cloning for gene encoding fungal β-1,6-glucanase by means of RT-PCR using specific primers

“…Pada bakteri misalnya, enzim ini terdapat dalam komplek multi enzim yang disebut selulosom dan terdiri dari beberapa subunit. Sedangkan selulase dari Trichoderma reesei mengandung dua eksoglukanase, paling sedikit empat endoglukanase dan satu β-glukosidase (Kumar et al, 2008).…”