Lignocellulosic materials are among the most promising alternative energy resources that can be utilized to produce cellulosic ethanol. However, the physical and chemical structure of lignocellulosic materials forms strong native recalcitrance and results in relatively low yield of ethanol from raw lignocellulosic materials. An appropriate pretreatment method is required to overcome this recalcitrance. For decades various pretreatment processes have been developed to improve the digestibility of lignocellulosic biomass. Each pretreatment process has a different specificity on altering the physical and chemical structure of lignocellulosic materials. In this paper, the chemical structure of lignocellulosic biomass and factors likely affect the digestibility of lignocellulosic materials are discussed, and then an overview about the most important pretreatment processes available are provided. In particular, the combined pretreatment strategies are reviewed for improving the enzymatic hydrolysis of lignocellulose and realizing the comprehensive utilization of lignocellulosic materials.

The role of pretreatment in improving the enzymatic hydrolysis

Key process parameters for deep eutectic solvents pretreatment of lignocellulosic biomass materials: A review.

Publisher: NPG; Journal: Nature: Nature; Article Type: Biology letter DOI: 10.1038/nature06269 Metagenomic and functional analysis of hindgut microbiota of a wood-feeding higher termite Falk Warnecke 1 *, Peter Luginbuhl 2 *, Natalia Ivanova 1 , Majid Ghassemian 2 , Toby H. Richardson 2 †, Justin T. Stege 2 , Michelle Cayouette 2 †, Alice C. McHardy 3 †, Gordana Djordjevic 2 , Nahla Aboushadi 2 , Rotem Sorek 1 , Susannah G. Tringe 1 , Mircea Podar 4 , Hector Garcia Martin 1 , Victor Kunin 1 , Daniel Dalevi 1 , Julita Madejska 1 , Edward Kirton 1 , Darren Platt 1 , Ernest Szeto 1 , Asaf Salamov 1 , Kerrie Barry 1 , Natalia Mikhailova 1 , Nikos C. Kyrpides 1 , Eric G. Matson 5 , Elizabeth A. Ottesen 6 , Xinning Zhang 5 , Myriam Hernandez 7 , Catalina Murillo 7 , Luis G. Acosta 7 , Isidore Rigoutsos 3 , Giselle Tamayo 7 , Brian D. Green 2 , Cathy Chang 2 †, Edward M. Rubin 1 , Eric J. Mathur 2 †, Dan E. Robertson 2 , Philip Hugenholtz 1 & Jared R. Leadbetter 5 * DOE Joint Genome Institute, 2800 Mitchell Drive, Walnut Creek, California 94598, USA. 2 Verenium Corporation (formerly Diversa), 4955 Directors Place, San Diego, California 92121, USA. 3 IBM Thomas J. Watson Research Center, PO Box 218, Yorktown Heights, New York 10598, USA. 4 Oak Ridge National Laboratory, Biosciences Division, Oak Ridge, Tennessee 37831-6026, USA. 5 Department of Environmental Science and Engineering, Division of Biology, Mailcode 138-78, California Institute of Technology, Pasadena, California 91125, USA. INBio, Instituto Nacional de Biodiversidad, Apdo. Postal 22-3100 Santo Domingo de Heredia, Costa Rica. †Present addresses: Synthetic Genomics, Inc., 11149 North Torrey Pines Road, Suite 100, La Jolla, California 92037, USA (T.H.R., E.J.M.); Max Planck Institute for Computer Science, Stuhlsatzenhausweg 85, 66123 Saarbrucken, Germany (A.C.M.); Stratagene, 11011 North Torrey Pines Road, La Jolla, California 92037, USA (M.C.); E. O. Wilson Foundation, 10190 Telesis Court, San Diego, California 92121, USA (C.C.). *These authors contributed equally to this work. From the standpoints of both basic research and biotechnology, there is considerable interest in reaching a clearer understanding of the diversity of biological mechanisms employed during lignocellulose degradation. Globally, termites are an extremely successful group of wood-degrading organisms 1 and are therefore important both for their roles in carbon turnover in the environment and as potential sources of biochemical catalysts for efforts aimed at converting wood into biofuels. Only recently have data supported any direct role for the symbiotic bacteria in the gut of the termite in cellulose and xylan hydrolysis 2 . Here we use a metagenomic analysis of the bacterial community resident in the hindgut paunch of a wood-feeding Nasutitermes species to show the presence of a large, diverse set of bacterial genes for cellulose and xylan hydrolysis. Many of these genes were expressed in vivo or had cellulase activity in vitro, and further analyses implicate spirochete and fibrobacter species in gut lignocellulose degradation. New insights into other important Page 1 of 33

Metagenomic and functional analysis of hindgut microbiota of a wood-feeding higher termite

Chemical, physical and biological methods to convert lignocellulosic waste into value-added products. A review

An eco-friendly biomass pretreatment strategy utilizing reusable enzyme mimicking nanoparticles for lignin depolymerization and biofuel production

Deciphering the aloe vera leaf rind as potent feedstock for bioethanol through enzymatic delignification and its enhanced saccharification

Uprising fossil fuel depletion and deterioration of ecological reserves supply have led to the search for alternative renewable and sustainable energy sources and chemicals. Although first generation biorefinery is quite successful commercially in generating bulk of biofuels globally, the food versus fuel debate has necessitated the use of non-edible feedstocks, majorly waste biomass, for second generation production of biofuels and chemicals. A diverse class of microbes and enzymes are being exploited for biofuels production for a series of treatment process, however, the conversion efficiency of wide range of lignocellulosic biomass (LCB) and consolidated way of processing remains challenging. There were lot of research efforts in the past decade to scour for potential microbial candidate. In this context, evolution has developed the gut microbiota of several insects and ruminants that are potential LCB degraders host eco-system to overcome its host nutritional constraints, where LCB processed by microbiomes pretends to be a promising candidate. Synergistic microbial symbionts could make a significant contribution towards recycling the renewable carbon from distinctly abundant recalcitrant LCB. Several studies have assessed the bioprospection of innumerable gut symbionts and their lignocellulolytic enzymes for LCB degradation. Though, some reviews exist on molecular characterization of gut microbes, but none of them has enlightened the microbial community design coupled with various LCB valorization which intensifies the microbial diversity in biofuels application. This review provides a deep insight into the significant breakthroughs attained in enrichment strategy of gut microbial community and its molecular characterization techniques which aids in understanding the holistic microbial community dynamics. Special emphasis is placed on gut microbial role in LCB depolymerization strategies to lignocellulolytic enzymes production and its functional metagenomic data mining eventually generating the sugar platform for biofuels and renewable chemicals production.

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Unlocking the potential of insect and ruminant host symbionts for recycling of lignocellulosic carbon with a biorefinery approach: a review.

Aloe vera rind (AVR), a discarded solid biomass after extraction of gel finds no commercial importance could serve as a potent lignocellulosic feedstock for bioethanol production that prerequisite an efficient pretreatment to remove the lignin (16.4%, w/w). In the present study, the impact of mild acid pretreatment on AVR by using microwave energy with varied power (160 W, 320 W and 480 W) and its efficiency on saccharification was evaluated. Microwave acid pretreatment resulted in threefold decrease in recalcitrant lignin (5.58%, w/w) at 480 W than untreated AVR biomass. The effect of pretreatment on AVR biomass was characterized by various analytical techniques. X-Ray Diffraction (XRD) patterns deciphered an increase in cellulose crystallinity (14.8%) of delignified AVR biomass as compared to raw biomass (10.5%) and the extent of structural distortion after pretreatment was clearly indicated by Scanning Electron Microscopy (SEM). Fourier-Transform Infra-Red (FTIR) spectra revealed the disappearance of peak around 1241 cm−1 (C–O stretching) indicated the deacetylation of hemicellulose after pretreatment. Gas Chromatography Mass Spectrometry (GC–MS) analysis of liquid hydrolysate obtained after pretreatment unveiled the presence of higher fraction of carboxylic acids, esters, aromatic and aliphatic hydrocarbons as a result of lignin oxidation. The maximum reducing sugar obtained by crude cellulase from the delignified AVR biomass was found to be 296.8 ± 1.26 mg/g as compared to untreated AVR biomass (129.68 ± 2.34 mg/g). This study has shown the acid microwave pretreatment of AVR biomass could effectively improve the yield of fermentable sugars that are further used for ethanol production.

Delignification of Aloe Vera Rind by Mild Acid Associated Microwave Pretreatment to Persuade Enhanced Enzymatic Saccharification

Sequential valorization strategies for dairy wastewater and water hyacinth to produce fuel and fertilizer

/pdf/synthesis-and-extraction-routes-of-allelochemicals-from-waz22oq1ab.pdf

Gunasekaran Rajeswari

Papers

Deciphering the aloe vera leaf rind as potent feedstock for bioethanol through enzymatic delignification and its enhanced saccharification

Unlocking the potential of insect and ruminant host symbionts for recycling of lignocellulosic carbon with a biorefinery approach: a review.

Delignification of Aloe Vera Rind by Mild Acid Associated Microwave Pretreatment to Persuade Enhanced Enzymatic Saccharification

Sequential valorization strategies for dairy wastewater and water hyacinth to produce fuel and fertilizer

Synthesis and extraction routes of allelochemicals from plants and microbes: A review