Biodegradation of alkaline lignin by Bacillus ligniniphilus L1 (original) (raw)
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Frontiers in Bioengineering and Biotechnology, 2020
There is increasing interest in research on lignin biodegradation compounds as potential building blocks in applications related to renewable products. More attention is necessary to evaluate the effects of the initial pH conditions during the bacterial degradation of lignin. In this study we performed experiments on lignin biodegradation under acidic and mild alkaline conditions. For acidic biodegradation, lignin was chemically pretreated with hydrogen peroxide. Alkaline biodegradation was achieved by developing the bacterial growth on Luria and Bertani medium with alkali lignin as the sole carbon source. The mutant strain Escherichia coli BL21(Lacc) was used to carry out lignin biodegradation over 10 days of incubation. Results demonstrated that under acidic conditions there was a predominance of aliphatic compounds of the C3–C4 type. Alkaline biodegradation was produced in the context of oxidative stress, with a greater abundance of aryl compounds. The final pH values of acidic and alkaline biodegradation of lignin were 2.53 and 7.90, respectively. The results of the gas chromatography mass spectrometry analysis detected compounds such as crotonic acid, lactic acid and 3-hydroxybutanoic acid for acidic conditions, with potential applications for adhesives and polymer precursors. Under alkaline conditions, detected compounds included 2-phenylethanol and dehydroabietic acid, with potential applications for perfumery and anti tumor/anti-inflammatory medications. Size-exclusion chromatography analysis showed that the weight-average molecular weight of the alkaline biodegraded lignin increased by 6.75-fold compared to the acidic method, resulting in a repolymerization of its molecular structure. Lignin repolymerization coincided with an increase in the relative abundance of dehydroabietic acid and isovanillyl alcohol, from 2.70 and 3.96% on day zero to 13.43 and 10.26% on 10th day. The results of the Fourier-transformed Infrared spectroscopy detected the presence of C = O bond and OH functional group associated with carboxylic acids in the acidic method. In the alkaline method there was a greater preponderance of signals related to skeletal aromatic structures, the amine functional group and the C – O – bond. Lignin biodegradation products from E. coli BL21(Lacc), under different initial pH conditions, demonstrated a promising potential to enlarge the spectrum of renewable products for biorefinery activities.
2009
Lignin is the most abundant aromatic polymer in nature. It is synthesized by higher plants, reaching levels of 20-30% of the dry weight of woody tissue, next to cellulose, is the second most abundant compound in plant biomass and a partial decay of lignin provides numerous aromatic monomers such as ferulic and vanillic acids. These aromatic compounds have attracted attention as renewable resources for the production of chemicals traditionally derived from petroleum. An Isolation and identification environmental friendly bacteria for lignin degradation becomes an essential, because all the previous researches concentrated on using fungal treatments. The importance of ligninolytic bacteria raised, because lignin-degrading bacteria have wider tolerance of temperature, pH and oxygen limitation than fungi. In addition, the application of fungi in bioleaching of raw pulp is not feasible due to its structural hindrance caused by fungal filament. One bacterial strain isolated from Egyptian ...
Lignin degradation: A microbial approach
Lignin is the most structurally complex carbohydrate consisting of various bilogically stable linkages. It has been estimated that lignin constitutes 30-35% of the earth’s non-fossil organic carbon. Lignin degradation plays an important role in carbon recycling and biofuel production. Industrial waste treatment through chemical approaches is not only expensive but also toxic to environment. Lignin degrading enzymes from microbes contribute a major role in the degradation of industrial effluents. Fungi and bacteria are good sources of effluent hydrolyzing enzymes such as lignin peroxidase, laccase, manganese peroxidase etc. However, there are very few research activities regarding role of microbes in lignin degradation. Lignin hydrolysis using various microbes with eco-friendly approach is a challenge for researchers globally. Therefore, in order to reduce the adverse effect of industrial effluent on environment, the quest for inexpensive, sustainable and eco-friendly approach is indispensable. The current review focuses to enlighten a comprehensive and broad analysis of lignin degradation ability of various fungal and bacterial sources using their ligninolytic machinery system.
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.
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.
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.
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.
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.
Lignin-Degrading Microorganisms from Organic Soils
International Journal of Plant & Soil Science, 2021
The most prevalent aromatic polymer in nature is lignin, produced by higher plants and thought to make up 30-35 percent of the non-fossil organic carbon on the planet. Lignin hydrolyzing enzymes such as lignin peroxidase, laccase, manganese peroxidase, and others produce a variety of aromatic monomers, including ferulic and vanillic acids. However, very little research has been done on the role of microbes in lignin degradation. In the present work, we have isolated 25 ligninolytic bacteria and 25 ligninolytic fungi from organic soils of Koppal, Raichur districts of Karnataka. The bacterial isolates were identified as Pseudomonas putida, Bacillus subtilis, based on biochemical tests, and fungi were identified as Aspergillus niger, Trichoderma viridae,Phanerochaetechrysosporiumand Pleurotusostreatusbased on morphological characters. The ligninolyticactivity of bacterial isolates was high when compared to fungal isolates. All the isolates produced detectable amounts of lignin peroxidase, manganese peroxidase, and laccase under in vitroconditions. In dye decolorization test, fungal isolates KGST-1, KGST-2, and KKSP could decolorize Ramazol Brilliant Blue R and Congo red.
Lignin Database for Diversity of Lignin Degrading Microbial Enzymes (LD 2 L
Lignin is the second most abundant constituent of the plant cell wall, where it protects cellulose against hydrolytic attack by saprophytic and pathogenic microbes. Lignin degradation plays a major role in carbon recycling in the ecosystem as well as convert plant biomass for second generation biofuel (ethanol) production. This environmentally recalcitrant organic material has been degraded by different microorganisms like, Bacteria, Fungi and Actinomycetes and they are capable of producing various degrading enzymes such as, Aryl oxidase, β-Glucosidse, Cellulase, Endoglucanase, Glycerol oxidase, Hemicellulase, Lignin peroxidase (LiP), Laccase, Manganese peroxidase, Oxylate decarboxylase and Xylanase. But the degradation process is controversial against different lignin due to its complex structure and bonding to carbohydrate complexes. To address this issue, we developed a lignin degrading microbial enzymes database which gives overall information about the diversity of lignin degrading enzymes of reported microbes. This database is made available through official Web server http://lignindegradingenzymesdatabase.zohosites.com/ for common use by the scientific community.