Decomposition of [14C]Lignocelluloses of Spartina alterniflora and a Comparison with Field Experiments

Decomposition of lignocelluloses from Spartina alterniflora in salt-marsh sediments was measured by using ¹⁴C-labeled compounds. Rates of decomposition were fastest in the first 4 days of incubation and declined later. Lignins labeled in side chains were mineralized slightly faster than uniformly labeled lignins; 12% of the [side chain-¹⁴C]lignin-labeled lignocellulose was mineralized after 816 h of incubation, whereas only 8% of the [U-¹⁴C]lignin-labeled lignocelluloses were degraded during this period. The carbohydrate moiety within the lignocellulose complex was degraded about four times faster than the lignin moiety; after 816 h of incubation, 29 to 37% of the carbohydrate moiety had been mineralized. Changes in concentration of lignin and cellulose in litter of S. alterniflora were followed over 2 years of decay. Cellulose disappeared from litter more rapidly than lignin; 50% of the initial content of cellulose was lost after 130 days, whereas lignin required 330 to 380 days for 50% loss. The slow loss of lignin compared with other litter components resulted in a progressive enrichment of litter in lignin content. The rates of mineralization of [¹⁴C]lignocelluloses in marsh sediments were similar to the rates of lignocellulose decomposition in litter on the marsh.     

Relative Contributions of Bacteria and Fungi to Rates of Degradation of Lignocellulosic Detritus in Salt-Marsh Sediments

Specifically radiolabeled [¹⁴C-lignin]lignocellulose and [¹⁴C-polysaccharide]lignocellulose from the salt-marsh cordgrass Spartina alterniflora were incubated with an intact salt-marsh sediment microbial assemblage, with a mixed (size-fractionated) bacterial assemblage, and with each of three marine fungi, Buergenerula spartinae, Phaeosphaeria typharum, and Leptosphaeria obiones, isolated from decaying S. alterniflora. The bacterial assemblage alone mineralized the lignin and polysaccharide components of S. alterniflora lignocellulose at approximately the same rate as did intact salt-marsh sediment inocula. The polysaccharide component was mineralized twice as fast as the lignin component; after 23 days of incubation, ca. 10% of the lignin component and 20% of the polysaccharide component of S. alterniflora lignocellulose were mineralized. Relative to the total sediment and bacterial inocula, the three species of fungi mediated only very slow mineralization of the lignin and polysaccharide components of S. alterniflora lignocellulose. Experiments with uniformly ¹⁴C-labeled S. alterniflora material indicated that the three fungi and the bacterial assemblage were capable of degrading the non-lignocellulosic fraction of S. alterniflora material, but only the bacterial assemblage significantly degraded the lignocellulosic fraction. Our results suggest that bacteria are the predominant degraders of lignocellulosic detritus in salt-marsh sediments.     

Anaerobic Biodegradation of the Lignin and Polysaccharide Components of Lignocellulose and Synthetic Lignin by Sediment Microflora

Specifically radiolabeled [¹⁴C-lignin]lignocelluloses and [¹⁴C-polysaccharide]lignocelluloses were prepared from a variety of marine and freshwater wetland plants including a grass, a sedge, a rush, and a hardwood. These [¹⁴C]lignocellulose preparations and synthetic [¹⁴C]lignin were incubated anaerobically with anoxic sediments collected from a salt marsh, a freshwater marsh, and a mangrove swamp. During long-term incubations lasting up to 300 days, the lignin and polysaccharide components of the lignocelluloses were slowly degraded anaerobically to ¹⁴CO₂ and ¹⁴CH₄. Lignocelluloses derived from herbaceous plants were degraded more rapidly than lignocellulose derived from the hardwood. After 294 days, 16.9% of the lignin component and 30.0% of the polysaccharide component of lignocellulose derived from the grass used (Spartina alterniflora) were degraded to gaseous end products. In contrast, after 246 days, only 1.5% of the lignin component and 4.1% of the polysaccharide component of lignocellulose derived from the hardwood used (Rhizophora mangle) were degraded to gaseous end products. Synthetic [¹⁴C]lignin was degraded anaerobically faster than the lignin component of the hardwood lignocellulose; after 276 days, 3.7% of the synthetic lignin was degraded to gaseous end products. Contrary to previous reports, these results demonstrate that lignin and lignified plant tissues are biodegradable in the absence of oxygen. Although lignocelluloses are recalcitrant to anaerobic biodegradation, rates of degradation measured in aquatic sediments are significant and have important implications for the biospheric cycling of carbon from these abundant biopolymers.     

Thermophilic Anaerobic Biodegradation of [14C]Lignin, [14C]Cellulose, and [14C]Lignocellulose Preparations

Thermophilic (55°C) anaerobic enrichment cultures were incubated with [¹⁴C-lignin]lignocellulose, [¹⁴C-polysaccharide]lignocellulose, and kraft [¹⁴C]lignin prepared from slash pine, Pinus elliottii, and ¹⁴C-labeled preparations of synthetic lignin and purified cellulose. Significant but low percentages (2 to 4%) of synthetic and natural pine lignin were recovered as labeled methane and carbon dioxide during 60-day incubations, whereas much greater percentages (13 to 23%) of kraft lignin were recovered as gaseous end products. Percentages of label recovered from lignin-labeled substrates as dissolved degradation products were approximately equal to percentages recovered as gaseous end products. High-pressure liquid chromatographic analyses of CuO oxidation products of sound and degraded pine lignin indicated that no substantial chemical modifications of the remaining lignin polymer, such as demethoxylation and dearomatization, occurred during biodegradation. The polysaccharide components of pine lignocellulose and purified cellulose were relatively rapidly mineralized to methane and carbon dioxide; 31 to 37% of the pine polysaccharides and 56 to 63% of the purified cellulose were recovered as labeled gaseous end products. An additional 10 to 20% of the polysaccharide substrates was recovered as dissolved degradation products. Overall, these results indicate that elevated temperatures can greatly enhance rates of anaerobic degradation of lignin and lignified substrates to methane and low-molecular-weight aromatic compounds.     

Preparation, Characterization, and Microbial Degradation of Specifically Radiolabeled [14C]Lignocelluloses from Marine and Freshwater Macrophytes

Specifically radiolabeled [¹⁴C-lignin]lignocelluloses were prepared from the aquatic macrophytes Spartina alterniflora, Juncus roemerianus, Rhizophora mangle, and Carex walteriana by using [¹⁴C]phenylalanine, [¹⁴C]tyrosine, and [¹⁴C]cinnamic acid as precursors. Specifically radiolabeled [¹⁴C-polysaccharide]lignocelluloses were prepared by using [¹⁴C]glucose as precursor. The rates of microbial degradation varied among [¹⁴C-lignin]lignocelluloses labeled with different lignin precursors within the same plant species. To determine the causes of these differential rates, [¹⁴C-lignin]lignocelluloses were thoroughly characterized for the distribution of radioactivity in nonlignin contaminants and within the lignin macromolecule. In herbaceous plants, significant amounts (8 to 24%) of radioactivity from [¹⁴C]phenylalanine and [¹⁴C]tyrosine were found associated with protein, although very little (3%) radioactivity from [¹⁴C]cinnamic acid was associated with protein. Microbial degradation of radiolabeled protein resulted in overestimation of lignin degradation rates in lignocelluloses derived from herbaceous aquatic plants. Other differences in degradation rates among [¹⁴C-lignin]lignocelluloses from the same plant species were attributable to differences in the amount of label being associated with ester-linked subunits of peripheral lignin. After acid hydrolysis of [¹⁴C-polysaccharide]lignocelluloses, radioactivity was detected in several sugars, although most of the radioactivity was distributed between glucose and xylose. After 576 h of incubation with salt marsh sediments, 38% of the polysaccharide component and between 6 and 16% of the lignin component (depending on the precursor) of J. roemerianus lignocellulose was mineralized to ¹⁴CO₂; during the same incubation period, 30% of the polysaccharide component and between 12 and 18% of the lignin component of S. alterniflora lignocellulose was mineralized.     

Effects of Selected Assay Parameters on Measurement of Lignocellulose Mineralization with a Radiolabeled Substrate

Varying the amount of labeled substrate or the amount of leaf material resulted in significant nonlinear changes in lignocellulose mineralization, as measured with natural [¹⁴C]lignin-labeled lignocellulose. The use of periodic rather than continuous aeration was found not to have significant effects on measured mineralization.     

Decomposition of [C]Lignocelluloses of Spartina alterniflora and a Comparison with Field Experiments

Decomposition of lignocelluloses from Spartina alterniflora in salt-marsh sediments was measured by using C-labeled compounds. Rates of decomposition were fastest in the first 4 days of incubation and declined later. Lignins labeled in side chains were mineralized slightly faster than uniformly labeled lignins; 12% of the [side chain-C]lignin-labeled lignocellulose was mineralized after 816 h of incubation, whereas only 8% of the [U-C]lignin-labeled lignocelluloses were degraded during this period. The carbohydrate moiety within the lignocellulose complex was degraded about four times faster than the lignin moiety; after 816 h of incubation, 29 to 37% of the carbohydrate moiety had been mineralized. Changes in concentration of lignin and cellulose in litter of S. alterniflora were followed over 2 years of decay. Cellulose disappeared from litter more rapidly than lignin; 50% of the initial content of cellulose was lost after 130 days, whereas lignin required 330 to 380 days for 50% loss. The slow loss of lignin compared with other litter components resulted in a progressive enrichment of litter in lignin content. The rates of mineralization of [C]lignocelluloses in marsh sediments were similar to the rates of lignocellulose decomposition in litter on the marsh.     

Decomposition of lignocellulose from a freshwater macrophyte by aero-aquatic fungi

Mineralization of uniformly radiolabeled [¹⁴C]lignocellulose and specifically radiolabeled [¹⁴C-lignin]lignocellulose from the freshwater sedgeCarex walteriana by five aero-aquatic fungi was investigated. The extent of mineralization varied among the five species from 2.2 to 4.2% for the lignin component and from 3.3 to 20.6% for the polysaccharide component. The extent of mineralization of both lignin and polysaccharide moieties by a mixed culture of the five fungi were generally markedly lower than by pure cultures, possibly due to the production of antimicrobial compounds.Spirosphaera foriformis, the most active strain in lignin as well as in polysaccharide mineralization, degraded ferulic acid faster than p-coumaric acid. Decomposition ofCarex walteriana lignocellulose by this strain resulted in decreased cinnamyl/vanillyl (C/V) and syringyl/vanillyl (S/V) ratios. Offprint requests to: M. Bergbauer.     

Effects of pH on Lignin and Cellulose Degradation by Streptomyces viridosporus

Lignocellulose degradation by Streptomyces viridosporus results in the oxidative depolymerization of lignin and the production of a water-soluble lignin polymer, acid-precipitable polymeric lignin (APPL). The effects of the culture pH on lignin and cellulose metabolism and APPL production by S. viridosporus are reported. Dry, ground, hot-water-extracted corn (Zea mays) lignocellulose was autoclaved in 1-liter reagent bottles (5 g per bottle) and inoculated with 50-ml volumes of S. viridosporus cells suspended in buffers of specific pH (pH 6.0 to 9.2 at 0.4 pH unit intervals). Four replicates of inoculated cultures and of uninoculated controls at each pH were incubated as solid-state fermentations at 37°C. After 6 weeks of incubation the percent loss of lignocellulose, lignin, and carbohydrate and the amount of APPL produced were determined for each replicate. Optimal lignocellulose degradation, as shown by substrate weight loss, was observed in the pH range of 8.4 to 8.8. Only minor differences were seen in the Klason lignin, carbohydrate, protein, and ash contents of the APPLS produced by cultures at each pH. The effects of pH on the degradation of a spruce (Picea pungens) [¹⁴C-lignin]lignocellulose and a Douglas fir (Pseudotsuga menziesii) [¹⁴C-glucan]-lignocellulose were also determined at pH values between 6.5 and 9.5 (0.5 pH unit intervals). The incubations were carried out for 3 weeks at 37°C with bubbler-tube cultures. The percentage of initial ¹⁴C recovered as ¹⁴CO₂, ¹⁴C-labeled water-soluble products, and [¹⁴C]APPL was then determined. The mineralization of lignin and cellulose to CO₂ was optimal at pHs 6.5 and 7.0, respectively. However, the optimum for lignin and cellulose solubilization was pH 8.5, which correlated with the pH 8.5 optimum for APPL production. Overall, the data show that, whereas lignin mineralization is optimal at neutral to slightly acidic pHs, lignocellulose degradation with lignin solubilization and APPL production is promoted by alkaline pHs. These findings indicate that lignin-solubilizing actinomycetes may play an important role in the metabolism of lignin in neutral to alkaline soils in which ligninolytic fungi are not highly competitive.     

Thermophilic anaerobic biodegradation of [C]lignin, [C]cellulose, and [C]lignocellulose preparations

Thermophilic (55 degrees C) anaerobic enrichment cultures were incubated with [C-lignin]lignocellulose, [C-polysaccharide]lignocellulose, and kraft [C]lignin prepared from slash pine, Pinus elliottii, and C-labeled preparations of synthetic lignin and purified cellulose. Significant but low percentages (2 to 4%) of synthetic and natural pine lignin were recovered as labeled methane and carbon dioxide during 60-day incubations, whereas much greater percentages (13 to 23%) of kraft lignin were recovered as gaseous end products. Percentages of label recovered from lignin-labeled substrates as dissolved degradation products were approximately equal to percentages recovered as gaseous end products. High-pressure liquid chromatographic analyses of CuO oxidation products of sound and degraded pine lignin indicated that no substantial chemical modifications of the remaining lignin polymer, such as demethoxylation and dearomatization, occurred during biodegradation. The polysaccharide components of pine lignocellulose and purified cellulose were relatively rapidly mineralized to methane and carbon dioxide; 31 to 37% of the pine polysaccharides and 56 to 63% of the purified cellulose were recovered as labeled gaseous end products. An additional 10 to 20% of the polysaccharide substrates was recovered as dissolved degradation products. Overall, these results indicate that elevated temperatures can greatly enhance rates of anaerobic degradation of lignin and lignified substrates to methane and low-molecular-weight aromatic compounds.     

Effects of Petroleum Hydrocarbons on Plant Litter Microbiota in an Arctic Lake

The effects of petroleum hydrocarbons on the microbial community associated with decomposing Carex leaf litter colonized in Toolik Lake, Alaska, were examined. Microbial metabolic activity, measured as the rate of acetate incorporation into lipid, did not vary significantly from controls over a 12-h period after exposure of colonized Carex litter to 3.0 ml of Prudhoe Bay crude oil, diesel fuel, or toluene per liter. ATP levels of the microbiota became elevated within 2 h after the exposure of the litter to diesel fuel or toluene, but returned to control levels within 4 to 8 h. ATP levels of samples exposed to Prudhoe Bay crude oil did not vary from control levels. Mineralization of specifically labeled ¹⁴C-[lignin]-lignocellulose and ¹⁴C-[cellulose]-lignocellulose by Toolik Lake sediments, after the addition of 2% (vol/vol) Prudhoe Bay crude oil, motor oil, diesel fuel, gasoline, n-hexane, or toluene, was examined after 21 days of incubation at 10°C. Diesel fuel, motor oil, gasoline, and toluene inhibited ¹⁴C-[lignin]-lignocellulose mineralization by 58, 67, 67, and 86%, respectively. Hexane-treated samples displayed an increase in the rate of ¹⁴C-[lignin]-lignocellulose mineralization of 33%. ¹⁴C-[cellulose]-lignocellulose mineralization was inhibited by the addition of motor oil or toluene by 27 and 64%, respectively, whereas diesel fuel-treated samples showed a 17% increase in mineralization rate. Mineralization of the labeled lignin component of lignocellulose appeared to be more sensitive to hydrocarbon perturbations than was the labeled cellulose component.     

Mineralization of Detrital Lignocelluloses by Salt Marsh Sediment Microflora

Specifically radiolabeled ¹⁴C-(cellulose)-lignocellulose and ¹⁴C-(lignin)-lignocellulose were isolated from labeled cuttings of Spartina alterniflora (cordgrass) and Pinus elliottii (slash pine). These were used to estimate the rates of mineralization to CO₂ of lignocelluloses of estuarine and terrestrial origin in salt marsh estuarine sediments. The lignin moiety of pine lignocellulose was mineralized 10 to 14 times more slowly than that of Spartina lignocellulose, depending on the source of inoculum. Average values for percent mineralization after 835 h of incubation were 1.4 and 13.9%, respectively. For Spartina lignocellulose, mineralization of the cellulose moiety was three times faster than that of the lignin moiety. Average values for percent mineralization after 720 h of incubation were 32.1 and 10.6%, respectively. Lignocellulose and lignin contents of live pine and Spartina plants were analyzed and found to be 60.7 and 20.9%, respectively, for pine and 75.6 and 15.1%, respectively, for Spartina.     

Lignin-solubilizing ability of actinomycetes isolated from termite (Termitidae) gut

The lignocellulose-degrading abilities of 11 novel actinomycete strains isolated from termite gut were determined and compared with that of the well-characterized actinomycete, Streptomyces viridosporus T7A. Lignocellulose bioconversion was followed by (i) monitoring the degradation of [14C]lignin- and [14C]cellulose-labeled phloem of Abies concolor to 14CO2 and 14C-labeled water-soluble products, (ii) determining lignocellulose, lignin, and carbohydrate losses resulting from growth on a lignocellulose substrate prepared from corn stalks (Zea mays), and (iii) quantifying production of a water-soluble lignin degradation intermediate (acid-precipitable polymeric lignin). The actinomycetes were all Streptomyces strains and could be placed into three groups, including a group of five strains that appear superior to S. viridosporus T7A in lignocellulose-degrading ability, three strains of approximately equal ability, and three strains of lesser ability. Strain A2 was clearly the superior and most effective lignocellulose decomposer of those tested. Of the assays used, total lignocellulose weight loss was most useful in determining overall bioconversion ability but not in identifying the best lignin-solubilizing strains. A screening procedure based on 14CO2 evolution from [14C-lignin]lignocellulose combined with measurement of acid-precipitable polymeric lignin yield was the most effective in identifying lignin-solubilizing strains. For the termite gut strains, the pH of the medium showed no increase after 3 weeks of growth on lignocellulose. This is markedly different from the pattern observed with S. viridosporus T7A, which raises the medium pH considerably. Production of extracellular peroxidases by the 11 strains and S. viridosporus T7A was followed for 5 days in liquid cultures.(ABSTRACT TRUNCATED AT 250 WORDS)     

Lignin solubilisation by Thermomonospora mesophila

Summary Thermomonospora mesophila degraded [¹⁴C]lignin-labelled wheat lignocellulose to yield high molecular weight water-soluble products and a small amount of ¹⁴CO₂. Solubilisation of [¹⁴C]lignin was found to be extracellular and inducible by growth on lignocellulose (straw) and hemicellulose (xylan), but was not correlated with xylanase or cellulase production.The acid-precipitable product of straw degradation by T. mesophila was found to be a complex of lignin, pentose-rich carbohydrate and protein with some similarity to humic acids. Solid-state ¹³C-NMR spectra of the dried product were generally similar to those of chemically extracted milled straw lignin but showed an increased content of carbonyl groups.The relationship between degradation and solubilisation of lignin is discussed and a role suggested for actinomycetes in humification and the exploitation of lignocellulose bioconversion.     

Lignin-solubilizing ability of actinomycetes isolated from termite (Termitidae) gut.

The lignocellulose-degrading abilities of 11 novel actinomycete strains isolated from termite gut were determined and compared with that of the well-characterized actinomycete, Streptomyces viridosporus T7A. Lignocellulose bioconversion was followed by (i) monitoring the degradation of [14C]lignin- and [14C]cellulose-labeled phloem of Abies concolor to 14CO2 and 14C-labeled water-soluble products, (ii) determining lignocellulose, lignin, and carbohydrate losses resulting from growth on a lignocellulose substrate prepared from corn stalks (Zea mays), and (iii) quantifying production of a water-soluble lignin degradation intermediate (acid-precipitable polymeric lignin). The actinomycetes were all Streptomyces strains and could be placed into three groups, including a group of five strains that appear superior to S. viridosporus T7A in lignocellulose-degrading ability, three strains of approximately equal ability, and three strains of lesser ability. Strain A2 was clearly the superior and most effective lignocellulose decomposer of those tested. Of the assays used, total lignocellulose weight loss was most useful in determining overall bioconversion ability but not in identifying the best lignin-solubilizing strains. A screening procedure based on 14CO2 evolution from [14C-lignin]lignocellulose combined with measurement of acid-precipitable polymeric lignin yield was the most effective in identifying lignin-solubilizing strains. For the termite gut strains, the pH of the medium showed no increase after 3 weeks of growth on lignocellulose. This is markedly different from the pattern observed with S. viridosporus T7A, which raises the medium pH considerably. Production of extracellular peroxidases by the 11 strains and S. viridosporus T7A was followed for 5 days in liquid cultures.(ABSTRACT TRUNCATED AT 250 WORDS)     

Impact of Nitrogen and Phosphorus on [14C]Lignocellulose Decomposition by Stream Wood Microflora

Nutritional and physical factors affecting the decomposition of [¹⁴C]lignocellulose prepared from Douglas fir (Pseudotsuga menziesii) were examined by incubating the labeled substrate with homogenized surface wood scrapings obtained from a Douglas fir log in a Pacific Northwest stream. Incubations were conducted in distilled water, in stream water collected from four different sources, or in a defined mineral salts solution with or without supplemental N (KNO₃). Decomposition rates of [¹⁴C]lignocellulose, as measured by ¹⁴CO₂ evolution, were greater in each of the four filter-sterilized sources of stream water than in distilled water alone. Decomposition experiments conducted in stream water media with the addition of defined mineral salts demonstrated that [¹⁴C]cellulose decomposition was stimulated 50% by the addition of either KNO₃ or KH₂PO₄/K₂HPO₄ and further enhanced (167%) by a combination of both. In contrast, [¹⁴C]lignin decomposition was stimulated (65%) only by the addition of both N and P. Decomposition of [¹⁴C]lignocellulose was greatest when supplemental KNO₃ was supplied in concentrations of at least 10.0 mg of N liter⁻¹ but not increased further by higher concentrations. The decomposition of [¹⁴C]lignocellulose increased as the incubation temperature was raised and NO₃⁻¹-N supplementation further increased these rates between three-and sevenfold over the range of temperatures examined (5 to 22°C). Accumulation of NH₄⁺ (2 to 4 mg of N liter⁻¹) was always observed in culture filtrates of incubations which had been supplemented with KNO₃, the quantity being independent of NO₃⁻ concentrations ≥ 10 mg of N liter⁻¹. The role of supplemental NO₃⁻ in the decomposition of [¹⁴C]lignocellulose is discussed in relation to wood decomposition and the low concentrations of N found in stream ecosystems of the Pacific Northwest.     

Improvements in and Environmental Applications of Double-Vial Radiorespirometry for the Study of Microbial Mineralization

Several variations in the scintillation mixture and the filter paper arrangements for double-vial radiorespirometry were compared. Improved efficiencies (44%) and shorter response times were found by adding wetting agents and methanolic NaOH to the scintillation mixture in the filter paper. The scintillation chemicals used did not contain dioxane and were found to be nontoxic to the test microbiota in this system. Covering the inner reaction vial with aluminum foil minimized the reduction in counting efficiency when testing colored or dense environmental samples. Mineralization rates were determined with ¹⁴C-labeled glucose, acetate, and glutamate and [¹⁴C]cellulose- and [¹⁴C]lignin-labeled lignocellulose for composting cow manure, forest soil, and arctic lake sediment microbiota. This improved method can be used in a variety of procedures involving the measurement of microbial mineralizations of organic compounds. Since no liquid scintillation cocktail is used for counting, the radioactive wastes are aqueous or can be incinerated, making disposal easy.     

Effects of temperature on microbial utilization of lignocellulosic detritus in a thermally impacted stream

The effects of temperature on rates of mineralization of [¹⁴C]lignocellulose were investigated in water and sediment from a thermally impacted stream and from a nearby unimpacted swamp at the Savannah River Plant, South Carolina. The temperature optimum for lignocellulose mineralization remained near 35°C at the unimpacted site throughout the sampling period from November 1986 to May 1987. The temperature optimum for lignocellulose mineralization in the thermally impacted stream was near 45°C when thermal effluents from a nuclear reactor were released to the stream, and was near 35°C when the reactor was not operating. Microbial populations capable of rapidly degrading lignocellulose at higher temperatures (45–55°C) developed between 9 and 27 days under conditions of thermal stress, indicating that under favorable conditions thermophilic microorganisms became dominant components of the microbiota. Removal of thermal stress for periods of 75 days or less resulted in a collapse of the thermophilic degrading population.     

The pentose phosphate pathway as a source of NADPH for lignin synthesis

The aim of this work was to investigate whether the pentose phosphate pathway provides reducing power for lignin synthesis. Explants of the stem of Coleus blumei and the storage tissue of Helianthus tuberosus were cultured for 4 days on media which caused extensive lignification. [3-³H]-glucose and either [3-¹⁴C]- or [U-¹⁴C]-glucose were supplied to such 4-day-cultured explants, and also to the roots of 5-day-old seedlings of Pisum sativum. Significant amounts of ³H and ¹⁴C were recovered in syringaldehyde, vanillin, p-hydroxybenzaldehyde, and ligothio-glycollic acid from the explants of Coleus and Helianthus; and in vanillin, p-hydroxybenzaldehyde, and milled-wood lignin from pea roots. The ³H/¹⁴C ratios in these derivatives and preparations of lignin are held to indicate that much of the reducing power for lignin synthesis comes from the pentose phosphate pathway.     

Microbial degradation of lignocellulose: the lignin component

A new procedure was developed for the study of lignin biodegradation by pure or mixed cultures of microorganisms. Natural lignocelluloses were prepared containing C in primarily their lignin components by feeding plants l-[U-C]phenylalanine through their cut stems. Lignin degradation was observed in numerous soils by monitoring evolution of CO(2) from [C]lignin-labeled oak (Quercus albus), maple (Acer rubrum), and cattail (Typha latifola). An organism (Thermonospora fusca ATCC 27730) that is known to degrade cellulose but not lignin was shown to grow on lignocellulose in the presence of [C]lignocelluloses without evolution of CO(2). A known lignin degrader (a white-rot fungus, Polyporus versicolor) was shown to readily evolve CO(2) from damp C-labeled cattail and C-labeled maple.