Acidic Versus Alkaline Bacterial Degradation of Lignin Through Engineered Strain E. coli BL21(Lacc): Exploring the Differences in Chemical Structure, Morphology, and Degradation Products (original) (raw)
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Lignin is the most abundant aromatic biopolymer in the biosphere and it comprises up to 30% of plant biomass. Although lignin is the most recalcitrant component of the plant cell wall, still there are microorganisms able to decompose it or degrade it. Fungi are recognized as the most widely used microbes for lignin degradation. However, bacteria have also been known to be able to utilize lignin as a carbon or energy source. Bacillus ligniniphilus L1 was selected in this study due to its capability to utilize alkaline lignin as a single carbon or energy source and its excellent ability to survive in extreme environments. To investigate the aromatic metabolites of strain L1 decomposing alkaline lignin, GC-MS analysis was performed and fifteen single phenol ring aromatic compounds were identified. The dominant absorption peak included phenylacetic acid, 4-hydroxy-benzoicacid, and vanillic acid with the highest proportion of metabolites resulting in 42%. Comparison proteomic analysis wa...
Initial Steps in the Pathway for Bacterial Degradation of Two Tetrameric Lignin Model Compounds
Applied and Environmental Microbiology, 1987
We investigated the metabolic route by which a lignin tetramer-degrading mixed bacterial culture degraded two tetrameric lignin model compounds containing 3-O--4 and 5-S biphenyl structures. The a-hydroxyl groups in the propane chain of both phenolic and nonphenolic tetramers were first oxidized symmetrically in two successive steps to give monoketones and diketones. These ketone metabolites were decomposed through C.(= O) -Cp cleavage, forming trimeric carboxyl acids which were further metabolized through another Ca(=O) Cgp cleavage. Dehydrodiveratric acid, which resulted from the cleavage of the carbon bonds of the nonphenol tetramer, was demethylated twice. Four metabolites of the phenolic tetramer were purified and identified. All of these were stable compounds in sterile mineral medium, but were readily degraded by lignin tetramer-degrading bacteria along the same pathway as the phenol tetramer. No monoaromatic metabolites accumulated. All metabolites were identified by mass and proton magnetic resonance spectrometry. The metabolic route by which the mixed bacterial culture degraded tetrameric lignin model compounds was different from the route of the main ligninase-catalyzed Ca{"Cp cleavage by Phanerochaete chrysosporium.
Lignin biodegradation and industrial implications
AIMS Environmental Science, 2014
Lignocellulose, which comprises the cell walls of plants, is the Earth's most abundant renewable source of convertible biomass. However, in order to access the fermentable sugars of the cellulose and hemicellulose fraction, the extremely recalcitrant lignin heteropolymer must be hydrolyzed and removed-usually by harsh, costly thermochemical pretreatments. Biological processes for depolymerizing and metabolizing lignin present an opportunity to improve the overall economics of the lignocellulosic biorefinery by facilitating pretreatment, improving downstream cellulosic fermentations or even producing a valuable effluent stream of aromatic compounds for creating value-added products. In the following review we discuss background on lignin, the enzymology of lignin degradation, and characterized catabolic pathways for metabolizing the by-products of lignin degradation. To conclude we survey advances in approaches to identify novel lignin degrading phenotypes and applications of these phenotypes in the lignocellulosic bioprocess.
Biodegradation of lignin by fungi, bacteria and laccases
Bioresource Technology, 2016
Indulin AT biodegradation by basidiomycetous fungi, actinobacteria and commercial laccases was evaluated using a suite of chemical analysis methods. The extent of microbial degradation was confirmed by novel thermal carbon analysis (TCA), as the treatments altered the carbon desorption and pyrolysis temperature profiles in supernatants. Laccase treatments caused only minor changes, though with increases occurring in the 850 °C and char precursor fractions. After fungal treatments, lignin showed a similar change in the TCA profile, along with a gradual decrease of the total carbon, signifying lignin mineralization (combined with polymerization). By contrast, bacteria produced phenolic monomers without their further catabolism. After 54 days of cultivation, a 20 wt.% weight loss was observed only for fungi, Coriolus versicolor, corroborating the near-80% carbon mass balance closure obtained by TCA. Compositional changes in lignin as a result of biodegradation were confirmed by Thermal Desorption (TD)-Pyrolysis-GC-MS validating the carbon fractionation obtained by TCA.
Microbial treatment of industrial lignin: Successes, problems and challenges
Renewable and Sustainable Energy Reviews, 2017
Lignin, one of the major components of plant/lignocellulosic biomass, is an irregular 3-D polymer comprised of potentially valuable phenolic monomers. Currently lignin and its colloidal solution in water, black liquor, obtained as by-products in many biomass treatment processes, e.g., pulping in paper industry, remain to be considered recalcitrant substrates of a limited commercial value. This study reviews the recent research on both fungal and bacterial lignin degradation, with a focus on the characterization of degradation products. The specific features and biological treatment of industrial lignin and black liquor are detailed along with the degradation conditions employed, complementing other review articles focusing on natural lignin degradation. An overview of ligninolytic enzymes frequently identified among microorganisms is presented, with the emphasis on factors responsible for their regulation and induction including the mediators involved and multienzyme systems employed by natural lignin degraders. Efficient regulation of ligninolytic enzymes can be achieved through the optimization of a cultivation medium composition with supplementation of strain specific stimulatory components such as salts, low molecular weight phenolic compounds and nutrition sources. Current research efforts in characterizing lignin degradation products are reviewed with the emphasis on both destructive and non-destructive gas chromatographic methods as they are essential for future detailed kinetic and mechanistic studies.
Polymer Degradation and Stability, 1998
Peroxidases and laccases are key enzymes in the lignin biodegradation process. They oxidize phenolic and non-phenolic lignin model compounds into their phenoxy and cation radicals, respectively. Further non-enzymatic evolution lead then to various C-C and ether bond cleavages. Nevertheless, almost no information on the structural alterations undergone in vitro or in situ by lignin after enzymatic catalysis is available. We report here on the molecular structure of lignin oxidized by various (per)oxidasic systems. The oxidizability of phenolic and non-phenohc structures of the guaiacyl and syringyl type in the lignin network will be discussed as well as the modification of the macromolecular properties of the polymer oxidized in situ or in isolated state. 0 1998 Elsevier Science Limited. All rights reserved
Lignin degrading by Enzymes and Microbes
Since most renewable carbon is either in lignin or in compounds protected by lignin, there is wider scope for degradation of lignin in a sustainable way. In this article, efforts are made to understand the gravity of the situation and various concepts to achieve these goals are narrated.
Bacterial degradation of lignin
Enzyme and Microbial Technology, 1988
During the year 1983, there was a breakthrough in the field of lignin biodegradation when fungal ligninases and their hydrogen peroxide requirement were described. A comparable progression has not yet occurred with ligninolytic bacteria, although it is expected to take place in the near future once depolymerizing enzymes are isolated. Several bacterial strains have been found to mineralize aerobically [14C-lignin]lignocellulose as well as 14C-labelled synthetic lignins, even though the most efficient are still far from reaching the rates exhibited by ligninolytic fungi. Actinomycetes follow a characteristic pattern of lignocellulose decomposition, with the release of lignin-rich, water-soluble fragments that are slowly metabolized thereafter. Research is being carried out to find the key enzymes involved in both lignin solubilization and mineralization by bacteria and uncover their mechanism of action. The ability of bacteria to grow on low-molecular-weight lignin oligomers as the sole source of carbon and energy indicates that bacteria produce enzymes catalysing cleavage of intermonomeric linkages. Various strains metabolize cyclic lignans, biphenyl structures, and other "dimeric" compounds, including those that possess the arylglycerol-fl-aryl ether (fl-O-4) linkage. Cleavage of the latter apparently is reductive, fl-O-4 dimers being metabolized by some bacteria through Cc~-Cfl cleavage. In contrast, no one has isolated a bacterium capable of decomposing a dimeric structure of the 1,2-diarylpropane-1,3-diol (fl-1) type, although strains metabolizing 1,2-diarylethane compounds have been found. In the absence of oxygen, only low-molecular-weight oligomers or chemically modified lignins are significantly degraded. The contribution of bacteria to the complete biodegradation of lignin in natural environments where fungi are also present is not known. However, bacteria seem to play a leading role in decomposing lignin in aquatic ecosystems.
Environmental Processes, 2017
In the present investigation, a suitable technology for biodegradation of lignin using laccase with the help of mediator 1-hydroxybenzotriazole (HOBT) for enhancing the degradation has been attempted. The results showed that biodegradation of lignin at the level of 91-98% could be achieved for different concentrations of laccase with optimized parameters of 5.0 mM HOBT at pH 7.0 and temperature at 32°C within 24 h. UV analysis confirmed the disappearance of the original peak indicating the breakdown of aromatic content of lignin to smaller components. Thermo-gravimetric and differential scanning calorimetric (TGA-DSC) analysis showed thermal stability of the compound while decomposing through six steps, at 137, 257, 417, 586, 699 and 759°C, leaving a final residue of about 46%. The DSC experiment recorded the starting of thermal denaturing temperature as 83.83°C. Results of Fourier transform infrared (FTIR) analysis detected the presence of hydroxyl group (at 2939-3420 cm −1), C=C, C-H, C-N and C-S stretching at 1505-1595 cm −1 , 1212 cm −1 , 2597-3272 cm −1 , indicating presence of phenolic and carboxylic acid groups during degradation. Gas Chromatography Mass Spectrometry (GCMS) confirmed the formation of various intermediates. Reduction of chemical oxygen demand (COD) and total organic carbon (TOC) at the level of 84 and 80% were observed, respectively. The present investigation is very useful in treating wastewater containing lignin.