Lignin degradeation by white rot fungi

Abstract. The wood-degrading white-rot fungus Phanerochaete chrysosporium , has been the subject of intensive research in recent years and, based upon isolation of the extracellular enzyme ligninase, major advances have now been made toward elucidating the mechanism by which this fungus degrades lignin. From these developments, a model emerges which could explain the process by which wood-degrading fungi in general, attack lignin.     

Cloning of cDNA Encoding CCoAOMT from Populus tomentosa and Down-regulation of Lignin Content in Transgenic Plant Expressing Antisense Gene (in English)

cDNA encoding caffeoyl CoA O-methyltransferase (CCoAOMT) from Chinese white poplar ( Populus tomentosa Carr.) was cloned by RT-PCR and sequenced. Northern analysis displayed that the CCoAOMT was expressed specifically in the developing secondary xylem and its expression was coincident with lignification. The antisense CCoAOMT cDNA was transformed into P. tremula×P. alba mediated by Agrobacterium tumefaciens (Smith et Townsend) Conn. Transgenic plants were identified with PCR, PCR-Southern and Southern analysis. Lignin content in 5- to 6-month-old transgenic plants was measured. One of the transgenic lines had significant reduction of 17.9% in Klason lignin content as compared with that of untransformed poplar. The results demonstrate that antisense repression of CCoAOMT is an efficient way to reduce lignin content for improving pulping property in engineered trees.     

Decomposition of sugarcane bagasse with lignocellulose-derived thermotolerant and thermoresistant Penicillia and Aspergilli

To promote the decomposition of sugarcane bagasse (SCB) for conversion into value-added products and to reduce waste, the capability of fungal mixes (FMs) to degrade SCB was examined. A total of 169 isolates from SCB and non-SCB were categorized as thermotolerant and thermoresistant. Thirty-six fungal candidates were screened for the presence of polyphenol oxidase, endoglucanase (EDN) and xylanase (XLN) activities, and EDN and XLN activities were quantitated. Five identified isolates (Aspergillus flavus AG10; Aspergillus niger AG68 & NB23; and Penicillium citrinum AG93 & AG140) were selected as the best enzyme producers, and 15 moderately to highly xylolytic, cellulolytic and ligninolytic isolates were added to construct FMs. Using a Taguchi design, the top ten reducing sugar-producing FMs (no. 12 showed the maximum amount of reducing sugar, at 2.11 mg g⁻¹, followed by no. 7, 15, 2, 16, 11, 13, 6, 4, & 8) were selected as potential agents for decomposition durations of 1, 2 and 3 months. The maximum decrease in SCB materials compared with the control was generated by FM 6 (9.08% cellulose reduction); FM 13 (21.03% hemicellulose reduction); and FM 16 (9.21% lignin reduction). These results indicate the potential use of SCB as a substrate for synergistic FMs. These FMs could be applied to the large-scale composting of SCB and other related agricultural residues, thus improving the biological pretreatment of lignocellulose.     

植物苯丙氨酸解氨酶(PAL)在细胞分化中的作用

烟草、丹参和甜叶菊愈伤组织在分化过程中一般都出现两个PAL活性高峰。第一高峰在培养第一、二、三天中出现;第二高峰在第十一天前后出现。前者在分化或不分化培养基中都存在,似与组织分化无关,后者只在分化条件下才有,似可作为组织启动分化的指示酶。分化程度不同的组织,PAL活性有很大差异,即将或刚分化的组织活性最高,随着分化的进程活性趋于降低,老化的组织甚至丧失活性。PAL活性、木质素合成和管状份子形成之间有着紧密的相关性。     

Does leaf quality mediate the stimulation of leaf breakdown by phosphorus in Neotropical streams?

1. Lowland tropical streams have a chemically diverse detrital resource base, where leaf quality could potentially alter the effect of high nutrient concentrations on leaf breakdown. This has important implications given the extent and magnitude of anthropogenic nutrient loading to the environment. 2. Here, we examine if leaf quality (as determined by concentrations of cellulose, lignin and tannins) mediates the effects of high ambient phosphorus (P) concentration on leaf breakdown in streams of lowland Costa Rica. We hypothesised that P would have a stronger effect on microbial and insect processing of high‐ than of low‐quality leaves. 3. We selected three species that represented extremes of quality as measured in leaves of eight common riparian species. Species selected were, from high‐ to low‐quality: Trema integerrima > Castilla elastica > Zygia longifolia. We incubated single‐species leaf packs in five streams that had natural differences in ambient P concentration (10–140 μg soluble reactive phosphorus (SRP) L^?1), because of variable inputs of solute‐rich groundwater and also in a stream that was experimentally enriched with P (approximately 200 μg SRP L^?1). 4. The breakdown rate of all three species varied among the six streams: T. integerrima (k‐values range: 0.0451–0.129 day^?1); C. elastica (k‐values range: 0.0064–0.021 day^?1); and Z. longifolia (k‐values range: 0.002–0.008 day^?1). Both ambient P concentration and flow velocity had significant effects on the breakdown rate of the three species. 5. Results supported our initial hypothesis that litter quality mediates the effect of high ambient P concentration on leaf processing by microbes and insects. The response of microbial respiration, fungal biomass and invertebrate density to high ambient P concentration was greater in Trema (high quality) than in Castilla or Zygia (low quality). Variation in flow velocity, however, confounded our ability to determine the magnitude of stimulation of breakdown rate by P. 6. Cellulose and lignin appeared to be the most important factors in determining the magnitude of P‐stimulation. Surprisingly, leaf secondary compounds did not have an effect. This contradicts predictions made by other researchers, regarding the key role of plant secondary compounds in affecting leaf breakdown in tropical streams.     

Mutational analysis of the stability of the H2A and H2B histone monomers

The eukaryotic histone heterodimer H2A-H2B folds through an obligatory dimeric intermediate that forms in a nearly diffusion-limited association reaction in the stopped-flow dead time. It is unclear whether there is partial folding of the isolated monomers before association. To address the possible contributions of structure in the monomers to the rapid association, we characterized H2A and H2B monomers in the absence of their heterodimeric partner. By far-UV circular dichroism, the H2A and H2B monomers are 15% and 31% helical, respectively—significantly less than observed in X-ray crystal structures. Acrylamide quenching of the intrinsic Tyr fluorescence was indicative of tertiary structure. The H2A and H2B monomers exhibit free energies of unfolding of 2.5 and 2.9 kcal mol^− 1, respectively; at 10 μM, the sum of the stability of the monomers is ∼ 60% of the stability of the native dimer. The helical content, stability, and m values indicate that H2B has a more stable, compact structure than H2A. The monomer m values are larger than expected for the extended histone fold motif, suggesting that the monomers adopt an overly collapsed structure. Stopped-flow refolding—initiated from urea-denatured monomers or the partially folded monomers populated at low denaturant concentrations—yielded essentially identical rates, indicating that monomer folding is productive in the rapid association and folding of the heterodimer. A series of Ala and Gly mutations were introduced into H2A and H2B to probe the importance of helix propensity on the structure and stability of the monomers. The mutational studies show that the central α-helix of the histone fold, which makes extensive intermonomer contacts, is structured in H2B but only partially folded in H2A.     

The effects of increasing swelling and anionic charges on the enzymatic hydrolysis of organosolv-pretreated softwoods at low enzyme loadings

Organosolv‐pretreated Lodgepole pine substrates were physically and chemically treated to increase their hydrophilicity and swelling as these are two substrate attributes which have been shown to improve cellulolytic hydrolysis. Surprisingly, mechanical treatment of the organosolv‐treated substrates by PFI‐mill refining did not significantly increase hydrolysis yields despite decreases in particle size and crystallinity and increases in swelling. However, sulfonation of the substrate did, significantly, increase enzymatic hydrolysis at loadings of both 5 and 2.5 FPU g⁻¹ cellulose (from 80% to 95% and from 35% to 80%, respectively). In addition, sulfonation resulted in an increase in the amount of free enzymes detected during the course of hydrolysis to a maximum of 80% after 72 h. This suggested that the beneficial effects of sulfonation were primarily due to a decrease in the non‐specific binding of the cellulases to the lignin. Biotechnol. Bioeng. 2011; 108:1549–1558. © 2011 Wiley Periodicals, Inc.     

Does elevated atmospheric CO2 concentrations affect wood decomposition?

This study was conducted to test the hypothesis that wood tissues generated under elevated atmospheric [CO₂] have lower quality and subsequent reduced decomposition rates. Chemical composition and subsequent field decomposition rates were studied for beech (Fagus sylvatica L.) twigs grown under ambient and elevated [CO₂] in open top chambers. Elevated [CO₂] significantly affected the chemical composition of beech twigs, which had 38% lower N and 12% lower lignin concentrations than twigs grown under ambient [CO₂]. The strong decrease in N concentration resulted in a significant increase in the C/N and lignin/N ratios of the beech wood grown at elevated [CO₂]. However, the elevated [CO₂] treatment did not reduce the decomposition rates of twigs, neither were the dynamics of N and lignin in the decomposing beech wood affected by the [CO₂] treatment, despite initial changes in N and lignin concentrations between the ambient and elevated [CO₂] beech wood. This revised version was published online in June 2006 with corrections to the Cover Date.     

UGPase和反义4CL基因对转基因烟草纤维素和木质素合成的调控

用根癌农杆菌介导法将源于紫穗槐的尿苷二磷酸葡萄糖焦磷酸化酶（UGPase）基因、反义4-香豆酸辅酶A连接酶（4CL）基因以及两者的双价基因分别转移至烟草中。PCR和Southern杂交检测证实外源基因已整合到转基因烟草基因组中。测定全纤维素和Klason木质素含量的结果显示,增强UGPase基因的表达可提高转基因植株的纤维素含量,但对木质素含量没有影响;抑制4CL基因的表达可显著降低转基因植株的木质素含量,但对纤维素含量没有影响;转移双价基因的转基因植株中纤维素含量增加而木质素含量降低。