Yoon Soo Kim

Characterization of anatomical features and silica distribution in rice husk using microscopic and micro-analytical techniques

Abstract Rice husk is a by-product of rice milling process, and a great resource as a raw biomass material for manufacturing value-added composite products. One of the potential applications is to use rice husk as filler for manufacturing lignocellulosic fiber–thermoplastic composites. This study was conducted to examine the silica distribution in rice husk in preparation to use it as reinforcing filler for thermoplastic polymers. Microscopic techniques, such as light microscopy, scanning electron microscopy and field-emission SEM (FE-SEM) were used to observe the surface and internal structure of rice husk. Microscopic examination showed that two main components of husk, lemma and palea consisted of outer epidermis, layers of fibers, vascular bundles, parenchyma cells, and inner epidermis, in sequence from the outer to the inner surface. Histochemical staining showed that epidermal and fiber cell walls were lignified, and the walls of parenchyma and lower epidermal cells were not lignified. The outer epidermal walls were extremely thick, highly convoluted and lignified. The outer surface of both lemma and palea were conspicuously ridged. The energy dispersive X-ray micro-analysis attached to the FE-SEM provided information on the distribution of silica in the husk. Most of the silica was present in the outer epidermal cells, being particularly concentrated in the dome-shaped protrusions. These observations provided valuable background information on the organization of husk tissues and the distribution of silica, which will help optimize processes related to the use of rice husk for making lignocellulosic fiber–thermoplastic composites in our future work.

Micromorphological characteristics of wood biodegradation in wet environments: a review.

SUMMARY Wood in wet environments is attacked and degraded by soft rot fungi and erosion and tunnelling bacteria, which are more tolerant to high moisture and reduced oxygen conditions than basidiomycetes, such as white and brown rot fungi. Since wood decaying basidiomycete fungi are normally more aggressive and can degrade wood faster than soft rot fungi and bacteria, wood in wet environments can survive for a relatively long time. Archaeological investigations show that wood buried deep in ocean sediments can survive for hundreds and even thousands of years. In this review degradation patterns of various types of microbial wood decay are briefly described, and examples of decay type(s) in wood exposed in various wet environments presented. It is important to understand biological wood decay in wet environments in order to find appropriate ways to prolong woodʼs service life and properly restore wooden artefacts.

Identification and Antimicrobial Activity of Phenylacetic Acid Produced by Bacillus licheniformis Isolated from Fermented Soybean, Chungkook-Jang

A bacterial strain, B65-1, which showed strong antimicrobial activity, was isolated from Chungkook-Jang, a traditional Korean fermented-soybean food with antimicrobial properties. Based on carbon utilization pattern and partial 16S rRNA sequence analysis, the B65-1 strain was identified as Bacillus licheniformis. An antibiotic compound, active against bacteria and yeast such as Staphylococcus aureus, Escherichia coli, and Candida albicans, was isolated by various chromatographic procedures from culture filtrates of B. licheniformis B65-1. The purified antibiotic was identified to be phenylacetic acid, with the molecular formula C8H8O2 by analyses of EI-MS and NMR. The phenylacetic acid was detected in fermented soybean made with the strain B65-1 as a starter, but was not present in extracts of nonfermented soybean. Our results indicated that the phenylacetic acid produced by B. licheniformis during fermentation of soybean is one of the main compounds of antimicrobial activity of Chungkook-Jang.

Micromorphological characteristics of decayed wood and laccase produced by the brown-rot fungus Coniophora puteana

Microscopic examination showed the cell wall decay pattern produced by the brown-rot fungus Coniophora puteana to be different from the degradation pattern known to be typical for brown-rot fungi. Erosion and thinning of cell walls in patterns considered to be characteristic of white-rot decay were observed. In particular, the fungal strain COP 20242 degraded secondary cell wall layers extensively, and also degraded lignin-rich middle lamellae. Some strains of C. puteana produced soft-rot type cavities in the S2 layer. All strains of C. puteana employed in the present work showed a positive reaction to tannic acid in the Bavendamm test, indicating the production of laccase. Microscopic and enzymatic studies provided evidence to suggest that the wood decay by C. puteana is unique both in terms of micromorphological and enzymatic patterns of cell wall degradation. This is because brown-rot fungi are not generally known to form cavities in the cell walls or to produce lignin-degrading enzymes. These observations suggest that lignin degradation capacity of brown-rot fungi may be greater than previously considered.

Bacteria as important degraders in waterlogged archaeological woods

An electron microscopic study of archaeological woods from different sites and of different ages revealed that the woods had been attacked by erosion bacteria, tunneling bacteria and soft rot fungi. Bacterial erosion appeared to be most widespread and was present independently as well as together with tunneling and soft rot attacks. Thus, in many instances bacterial erosion was the only type of microbial attack present. This work recognizes the important role bacteria play generally, and erosion bacteria particularly, in the deterioration of waterlogged archaeological woods.

Differential Scanning Calorimetry of Phenol-Formaldehyde (PF) Adhesives

This paper discusses theoretical background of differential scanning calorimetry (DSC) and its application for phenol-formaldehyde (PF) adhesives to characterize their thermal curing behaviors. Three different scanning methods (single-heating rate, multi-heating rate and isothermal method) of DSC were used for liquid and powdered PF resins. The result showed that the single-heating rate method gave larger activation energy compared with that of the multi-heating rate method. The multi-heating rate method was successfully employed for the thermal characterization of powdered PF resin that showed two distinctive exothermic peaks. The isothermal method can provide an insight for how PF resin cures in hot-pressing process.

Cytochemical Localization of Hydrogen Peroxide Production during Wood Decay by Brown-Rot Fungi Tyromyces palustris and Coniophora puteana

Summary It is not definitively known whether or not the production of extracellular hydrogen peroxide (H2O2) is a universal characteristic of brown-rot fungi. Cytochemical localization of H2O2 was tested in two brown-rot fungi, Tyromyces palustris and Coniophora puteana, by staining with cerium chloride. Transmission electron microscopy (TEM) showed the deposition of cerium perhydroxide within the fungal hyphae as well as wood cell walls affected by brown-rot fungi. TEM work indicated that extracellular H2O2 was present in brown-rot fungi and that H2O2 from brown-rot fungi diffused into the wood cell walls in the early stages of decay. The present work strongly suggests that H2O2 plays an important role in the early degradation of cellulose by brown-rot fungi. The usefulness of this technique for localizing H2O2 at high resolution with minimal nonspecific deposition is also discussed.

Micromorphological characteristics and lignin distribution in bamboo (Phyllostachys pubescens) degraded by the white rot fungus Lentinus edodes

Abstract Little is known about the decay pattern of bamboo by wood decay fungi, and the information available on fungal degradation of wood from other plant taxa cannot form the basis for understanding wood decay in bamboo because of differences in lignin composition and distribution. The present work was undertaken to elucidate the degradation pattern of bamboo by a lignin-degrading white rot fungus Lentinus edodes using various microscopic techniques, with a particular focus on the relation of bamboo lignin composition to the decay patterns produced by this fungus. Small blocks of bamboo, Phyllostachys pubescens, were examined after 16 weeks of incubation with the white rot fungus L. edodes. The compound middle lamellae (CML), including the cell corner regions, were preferentially degraded at an early stage of decay, whereas the fiber secondary walls remained largely intact at this point. Bamboo fiber walls were also eroded from the cell lumen side but the extent of degradation was limited. The FT-IR bands assigned to lignin exhibited a significant decrease. Cellular ultraviolet microspectrophotometric investigation showed that CML and vessel walls were composed of not only guaiacyl and syringyl unit (GS lignin) but also grass lignin. In contrast, the secondary wall of fibers consisted mainly of the GS lignin. Even though the CML and vessel walls exhibited higher lignin concentration, these cell walls were nevertheless degraded. The preferential degradation of the CML over the fiber secondary walls strongly suggested the involvement of not only enzyme systems of the white rot fungus but also a relationship to physicochemical properties of bamboo cell walls, particularly the influence of lignin composition and distribution.

The Bremen Cog of 1380 – An electron microscopic study of its degraded wood before and after stabilization with PEG

Abstract The Bremen Cog is a big ship built AD 1380 from oak wood. After its recovery from the river Weser, the water-logged ships timbers were successfully stabilized using a novel two-step polyethylene glycol (PEG) treatment. An electron microscopic study of the patterns of degradation and of the distribution of PEG within the Cog wood is described. Descriptions like these do not exist for many well known archaeological objects. SEM revealed that in areas with extensive degradation, wood cell walls are thinned and cells have a distorted appearance. TEM provided evidence that the wood has been degraded primarily by erosion bacteria. The stabilization treatment involved impregnation first with PEG 200 and then with PEG 3000. The SEM observations of PEG-impregnated wood revealed that in degraded tissues all cell types are well filled with PEG 3000. Non-degraded tissues are impermeable to PEG 3000 and are impregnated only with PEG 200. SEM confirmed earlier fluorescence microscopic evidence, that PEG 200 is absorbed by the cell walls.

The mechanism of xylans removal during hydrothermal pretreatment of poplar fibers investigated by immunogold labeling

Main conclusionHydrothermal pretreatment initially removed the lignin-free xylan from the middle layer of secondary wall, followed by the lignin-bound xylan, but the cellulose-bound xylan was seldom removed by this pretreatment.An in-depth understanding of the mechanism of xylan removal during hydrothermal pretreatment (HTP) of wood is critical for cost-effective conversion of lignocellulosic biomass to biofuels. Several studies demonstrated the kinetics and mechanism of xylan removal during HTP on molecular scale, but the dissolution mechanism of xylan during HTP remains unclear at ultra-structural level. Our study investigated changes in the micro-distribution of xylan in poplar fiber cell walls during HTP by transmission electron microscopy (TEM) in combination with immunogold labeling. The study revealed that HTP caused greater decline in the density of xylan labeling in the S2 layer of fiber wall than in the S1 layer. There was a greater loss in the density of xylan labeling during HTP in the delignified and enzymatically treated fibers compared to untreated fibers. We propose that in the initial stages of HTP lignin-free xylan in the S2 layer was more readily hydrolyzed than in the S1 layer by hydronium ions. With increasing pretreatment time, the xylan covalently bound to lignin was also removed from the S2 layer due to the dissolution of lignin. The xylan tightly bound to cellulose was seldom removed during HTP, but was hydrolyzed in subsequent enzymatic treatment. This TEM-immunolabeling investigation reveals the manner in which different xylan fractions are removed from fiber cell wall during HTP, and we expect the information to be helpful in developing processes tailored for more effective conversion of cellulosic biomass into fermentable sugars.