Initial Steps in the Pathway for Bacterial Degradation of Two Tetrameric Lignin Model Compounds (original) (raw)
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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.
Biodegradation of alkaline lignin by Bacillus ligniniphilus L1
Biotechnology for biofuels, 2017
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...
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.
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.
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
Limited bacterial mineralization of fungal degradation intermediates from synthetic lignin
Applied and Environmental Microbiology, 1991
The ability of selected bacterial strains and consortia to mineralize degradation intermediates produced by Phanerochaete chrysosporium from 14C-labeled synthetic lignins was studied. Three different molecular weight fractions of the intermediates were subjected to the action of the bacteria, which had been grown on a lignin-related dimeric compound. Two consortia isolated from wood being decayed naturally by a Ganoderma species of white rot fungus (the palo podrido system) mineralized 10 to 11% of the fraction with a molecular weight of approximately 500 but less than 4% of the higher- and lower-molecular-weight fractions. The consortia mineralized 5 to 9% of the original lignins. The ability of two pseudomonads isolated earlier from lignin-rich environments to mineralize the original lignins or fungus degradation products was much lower.
Applied and Environmental Microbiology
A simplified procedure for the identification and measurement of single-ring aromatic products of lignin acidolysis is described. The procedure employed a 6-h hydrolysis of spruce milled wood lignin in acidic dioxane at 8rC, followed by a series of organic extractions to recover acidolysis products which were quantified by gas chromatography of trimethylsilyl derivatives. Complex gel permeation chromatography procedures utilized by other workers were avoided in the modified procedu're, but equivalent results were obtained. The simplified procedure was utilized to hydrolyze sound and actinomycete-decayed spruce milled wood lignins and was shown to be useful as a technique for the rapid screening of microorganisms for their ability to alter lignin.
Utilization of dimeric lignin model compounds by mixed bacterial cultures
Applied Microbiology and Biotechnology, 1984
The degradation of dimeric phenylpropanoid lignin model compounds using mixed bacterial cultures was studied. The six model compounds contained the most common linkages of lignin: fl-O-4, fl-fl, fl-5, and fl-1. The results indicate that it is possible to enrich bacteria which are able to degrade all these compounds. Bacteria were also able to use these dimers as the sole source of carbon for growth. In view of these results it seems probable that bacterial inability to degrade polymeric lignin is due to the physical properties such as the molecular size of lignin.
Oxidation of phenolic compounds by ligninase
Journal of Biotechnology, 1990
The kinetics of oxidation of phenolic compounds by ligninase was investigated in the presence and absence of dimethoxylated compounds (veratryl alcohol and 3,4-dimethoxyphenyl acetic acid). In all cases, the phenolic compounds were found to be preferentially oxidised compared to the dimethoxylated compounds. Veratryl alcohol but not 3,4-dimethoxyphenyl acetic acid enhanced their oxidation, but only when present in at least 200-fold molar excess compared with the phenolic compounds. Ligninase was inactivated in the course of oxidation of the phenolic compounds. Inactivation was associated with the accumulation of compound III, formed by reaction of compound II with H20 2. Inactivation was reversed with additions of more enzyme but not with additions of veratryl alcohol. Evidence of inactivation was also obtained during the course of veratryl alcohol oxidation, but the extent was much less, supporting the concept of a substrate-modified compound II intermediate able to promote reaction with reductant over reaction with H20 2. A model to describe the mechanism by which ligninase catalyses net depolymerisation of lignin as opposed to further polymerisation is presented. It involves spatial separation between ligninase, lignin and phenolic lignin breakdown products and invokes the concepts of radical cations as mediators between enzyme and lignin as well as of radical cation charge transfer reactions through the structure of lignin.