Oxidative Depolymerization of Kraft Lignin for Microbial Conversion (original) (raw)
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Bacterial conversion of depolymerized Kraft lignin
Biotechnology for Biofuels
Background: Lignin is a potential feedstock for microbial conversion into various chemicals. However, the degradation rate of native or technical lignin is low, and depolymerization is needed to obtain reasonable conversion rates. In the current study, base-catalyzed depolymerization-using NaOH (5 wt%)-of softwood Kraft lignin was conducted in a continuous-flow reactor system at temperatures in the range 190-240 °C and residence times of 1 or 2 min. The ability of growth of nine bacterial strains belonging to the genera Pseudomonas and Rhodococcus was tested using the alkaline-treated lignin as a sole carbon source. Results: Pseudomonas fluorescens and Rhodococcus opacus showed the best growth of the tested species on plates with lignin. Further evaluation of P. fluorescens and R. opacus was made in liquid cultivations with depolymerized lignin (DL) at a concentration of 1 g/L. Size exclusion chromatography (SEC) showed that R. opacus consumed most of the available lower molecular weight compounds (approximately 0.1-0.4 kDa) in the DL, but the weight distribution of larger fractions was almost unaffected. Importantly, the consumed compounds included guaiacol-one of the main monomers in the DL. SEC analysis of P. fluorescens culture broth, in contrast, did not show a large conversion of low molecular weight compounds, and guaiacol remained unconsumed. However, a significant shift in molecular weight distribution towards lower average weights was seen. Conclusions: Rhodococcus opacus and P. fluorescens were identified as two potential microbial candidates for the conversion/consumption of base-catalyzed depolymerized lignin, acting on low and high molecular weight lignin fragments, respectively. These findings will be of relevance for designing bioconversion of softwood Kraft lignin.
Depolymerization of Kraft Lignin with Laccase and Peroxidase: A Review
2018
Lignin is a complex aromatic polymer of phenyl propene units non-linear and randomly linked. The main building blocks are p-coumaryl alcohol, coniferyl alcohol and sinapyl alcohol. Lignin is the third most abundant biopolymer on earth and usually accounts for 15-35% of the lignocellulose biomass. The degradation of lignin is extremely difficult due to the complexity of the chemical structure (variable upon the source) and the high molecular weight. Two major types of enzymes involved in the depolymerization of lignin are oxidoreductase: laccase and peroxidase, the main microbial producers being fungi and some bacteria. Due to its highly branched structure, lignin is considered to be the most recalcitrant component of lignocellulose, most of it not being recovered. Therefore, there’s a demand for more effective methods for depolymerization of lignin in order to obtain value-added products. This review underlines the importance of valorization of lignin through enzymatic depolymerizat...
Lignin depolymerization and utilization by bacteria
Bioresource technology, 2018
Lignin compound wastes are generated as a result of agricultural and industrial practices. Microorganism-mediated bio-catalytic processes can depolymerize and utilize lignin eco-friendly. Although fungi have been studied since several decades for their ability to depolymerize lignin, strict growth conditions of fungus limit it's industrial application. Compared with fungi, bacteria can tolerate wider pH, temperature, oxygen ranges and are easy to manipulate. Several studies have focused on bacteria involved in the process of lignin depolymerization and utilization. Pseudomonas have been used for paper mill wastewater treatment while Rhodococcus are widely reported to accumulate lipid. In this review, the recent studies on bacterial utilization in paper wastewater treatment, lignin conversion to biofuels, bioplastic, biofertilizers and other value-added chemicals are summarized. As bacteria possess remarkable advantages in industrial production, they may play a promising role in ...
Bioresource Technology Reports, 2019
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MOESM1 of Bacterial conversion of depolymerized Kraft lignin
2019
Additional file 1: Figure S1. (a) The SEC chromatogram of 1 g/L depolymerized (at 220 °C, 5 mL/min) lignin. Red-dotted lines represent the fractions collected. The collected fraction at 95–108 minutes corresponds to the 0.2–0.4 kDa peak in the SEC chromatograms calibrated with PEG standards. (b) UHPLC chromatograms of the fractions obtained from SEC. The peaks in the fraction 95–108 minutes correspond to aromatic monomers (Vanillin-3.5 min; guaiacol-4.6 min; acetovanillone-4.7 min). Table S1. Results of homology BLAST with the previously well-characterized DyP proteins against the genome of the organisms used in this study. P. putida EM42 strain used in this study is the modified version of KT2440 and hence, the genome of KT2440 (parental strain) was used for BLAST searches. Proteins with identity more than 75 % are emphasized in green. Proteins that were found absent and the ones with less than 30 % query are highlighted in red. P. fluorescens highlighted in blue is the only organi...
Fungal Biotransformation of Insoluble Kraft Lignin into a Water Soluble Polymer
Industrial & Engineering Chemistry Research, 2017
Low substrate solubility and slow decomposition/ biotransformation rate are among the main impediments for industrial scale lignin biotreatment. The outcome and dynamics of Kraft lignin biomodification by basidiomycetous fungi, Coriolus versicolor, were investigated in the presence of dimethyl sulfoxide (DMSO). The addition of 2 vol% DMSO to aqueous media increased the lignin solubility up to 70%, while the quasi-immobilized fungi (pre-grown on agar containing Kenaf biomass) maintained their ability to produce lignolytic enzymes. Basidiomycetous fungi were able to grow on solid media containing both 5-25 g/L lignin and up to 5 vol% DMSO, in contrast to no growth in liquid media as a free suspended culture. When a fungal culture pre-grown on agar was used for lignin treatment in an aqueous medium containing 2-5% DMSO with up to 25 g/L of lignin, significant lignin modification was observed in 1-6 days. The product analysis suggests that lignin was biotransformed, rather than biodegraded, into an oxygenated and crosslinked phenolic polymer. The resulting product showed the removal of phenolic monomers and/or their immediate precursors based on gas chromatography and thermal desorptionpyrolysisgas chromatographymass spectrometry analyses. Significant intramolecular cross-linking among the reaction products was shown by thermal carbon analysis
Mechanochemical Treatment Facilitates Two-Step Oxidative Depolymerization of Kraft Lignin
ACS Sustainable Chemistry & Engineering, 2018
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Base-Catalyzed Depolymerization of Solid Lignin-Rich Streams Enables Microbial Conversion
ACS Sustainable Chemistry & Engineering, 2017
Lignin valorization offers significant potential to enhance the economic viability of lignocellulosic biorefineries. However, because of its heterogeneous and recalcitrant nature, conversion of lignin to value-added coproducts remains a considerable technical challenge. In this study, we employ basecatalyzed depolymerization (BCD) using a process-relevant solid lignin stream produced via deacetylation, mechanical refining, and enzymatic hydrolysis to enable biological lignin conversion. BCD was conducted with the solid lignin substrate over a range of temperatures at two NaOH concentrations, and the results demonstrate that the lignin can be partially extracted and saponified at temperatures as low as 60°C. At 120°C and 2% NaOH, the high extent of lignin solubility was accompanied by a considerable decrease in the lignin average molecular weight and the release of lignin-derived monomers including hydroxycinnamic acids. BCD liquors were tested for microbial growth using seven aromatic-catabolizing bacteria and two yeasts. Three organisms (Pseudomonas putida KT2440, Rhodotorula mucilaginosa, and Corynebacterium glutamicum) tolerate high BCD liquor concentrations (up to 90% v/v) and rapidly consume the main ligninderived monomers, resulting in lignin conversion of up to 15%. Furthermore, as a proof of concept, muconic acid production from a representative lignin BCD liquor was demonstrated with an engineered P. putida KT2440 strain. These results highlight the potential for a mild lignin depolymerization process to enhance the microbial conversion of solid lignin-rich biorefinery streams.
Lignin is the most abundant aromatic biopolymer on Earth, and its aromatic structure makes it a promising platform for the production of biobased chemicals and other valuable building blocks. The valorization of lignin into chemicals currently presents a challenge, and its facilitation is key in the development of viable lignocellulosic biorefinery processes. This study presents a conceptual design for a recently demonstrated process for lignin oxidative depolymerization. Modeling, simulation, and analysis were performed based on experimental data to assess the viability of the process. Mass and energy balances and main design data were determined for a 700 t/ y kraft lignin biorefinery. The production capacity of aromatic chemicals, including vanillin, vanillic acid, guaiacol, and acetovanillone, was 0.3 kg aromatics/kg net lignin use. A heat-integrated process design is suggested, and the energy demands and the CO 2 emissions are evaluated and compared. Assuming an interest rate of 10% and a plant lifetime of 10 years, the return on investment was calculated to be 14%, indicating that such a biorefinery is viable. A sensitivity analysis was carried out to assess the impact of the vanillin selling price and the cost of lignin on the profitability of the process. A quantitative investigation of process sustainability resulted in an Efactor of ∼1.6 for the entire synthetic route, that is, 38% material efficiency. The findings of this study underline the need for further research to develop efficient lignin conversion technologies with attractive yields in order to increase profitability on an industrial scale.