Various agricultural residues, such as corn fiber, corn stover, wheat straw, rice straw, and sugarcane bagasse, contain about 20–40% hemicellulose, the second most abundant polysaccharide in nature. The conversion of hemicellulose to fuels and chemicals is problematic. In this paper, various pretreatment options as well as enzymatic saccharification of lignocellulosic biomass to fermentable sugars is reviewed. Our research dealing with the pretreatment and enzymatic saccharification of corn fiber and development of novel and improved enzymes such as endo-xylanase, β-xylosidase, and α-l-arabinofuranosidase for hemicellulose bioconversion is described. The barriers, progress, and prospects of developing an environmentally benign bioprocess for large-scale conversion of hemicellulose to fuel ethanol, xylitol, 2,3-butanediol, and other value-added fermentation products are highlighted.

Hemicellulose bioconversion

Multiplicity of beta-1,4-xylanase in microorganisms: functions and applications.

The development of new analytical techniques and the commercial availability of new substrates have led to the purification and characterization of a large number of xylan-degrading enzymes. Furthermore, the introduction of recombinant DNA technology has resulted in the selection of xylanolytic enzymes that are more suitable for industrial applications. For a successful integration of xylanases in industrial processes, a detailed understanding of the mechanism of enzyme action is, however, required. This review gives an overview of various xylanolytic enzyme systems from bacteria and fungi that have been described recently in more detail.

Xylanolytic enzymes from fungi and bacteria.

Clostridial acetone/butanol fermentation used to rank second only to ethanol fermentation by yeast in its scale of production and thus is one of the largest biotechnological processes known Its decline since about 1950 has been caused by increasing substrate costs and the availability of much cheaper feedstocks for chemical solvent synthesis by the petrochemical industry The so-called oil crisis in 1973 led to renewed interest in novel fermentation and product recovery technologies as well as in the metabolism and genetics of the bacterial species involved As a consequence, almost all of the enzymes leading to solvent formation are known, their genes have been sequenced (in fact, Clostridium acetobutylicum has been recently included in the microbial genome sequencing project), the regulatory mechanisms controlling solventogenesis have begun to emerge and recombinant DNA techniques have been developed for these clostridia to construct specific production strains In parallel, cheap agricultural-waste-based feedstocks have been exploited for their potential as novel substrates, continuous culture methods have been successfully established and new on-line product recovery technologies are now available, such as gas stripping, liquid/liquid extraction, and membrane-based methods In combination with these achievements, a reintroduction of acetone/butanol fermentation on an industrial scale seems to be economically feasible, a view that is supported by a new pilot plant in Austria recently coming into operation

New insights and novel developments in clostridial acetone/butanol/isopropanol fermentation

Although this review focusses primarily on bacterial cellulases and xylanases, there is considerable overlap in the molecular biology and biochemistry of prokaryotic and fungal forms of these enzymes. Therefore, fungal plant cell wall hydrolases are discussed where comparisons with the corresponding bacterial enzymes are important. Cellulases and xylanases encompass a collection of enzymes whose primary function is to hydrolyse p1,4-glycosidic linkages in the major plant structural polysaccharides, cellulose and xylan. In converting cellulose and xylan to their constituent sugars, these enzymes play an essential role in the digestive processes of herbivores and in the recycling of photosynthetically fixed carbon. The past decade has seen a burgeoning interest in all aspects of the biochemistry and molecular biology of cellulases and xylanases, which at first glance is rather perplexing. As a paradigm for p1,4glycanases, lysozyme is the enzyme of choice; it has been studied in greater detail than cellulases or xylanases and has a clearly understood catalytic mechanism. The recent discoveries from analysis of gene sequences and the three-dimensional structure of cellulase proteins show, however, that there is much to be understood about the enzymic hydrolysis of plant carbohydrate polymers beyond what can be adduced from analogy with lysozyme. To really appreciate the rationale behind current studies of microbial cellulases and xylanases, it is necessary to take a broad view that takes into account not just their intrinsic interest, but also their undoubted commercial potential. The structural polysaccharides cellulose and hemicellulose (xylan being the major

Bacterial cellulases and xylanases

An α-L-arabinofuranosidase (EC 3.2.1.55) has been purified from the extracellular culture fluid of Clostridium acetobutylicum ATCC 824 and characterized. The enzyme was a single polypeptide with a molecular weight of 94 000, an isoelectric point of 8.15, and a pH optimum between pH 5.0 and 5.5. The Km and Vmax values for p-nitrophenyl-α-L-arabinofuranoside were 4.0 mM and 36.4 μmol∙min−1·mg protein−1, respectively. The enzyme had practically no activity against other p-nitrophenylglycosides with the exception of p-nitrophenyl-α-D-glucoside which it hydrolysed at 9% of the rate exhibited on p-nitrophenyl-α-L-arabinofuranoside. It degraded arabinan in an exo-manner, but exhibited no activity on carboxymethylcellulose, arabinogalactan, arabinoxylan, or oat spelt xylan. However, when it was incubated with the purified xylanase B, also obtained from C. acetobutylicum, it acted cooperatively to increase the rate of hydrolysis of oat spelt xylan. Arabinose was detected as one of the hydrolysis products.

Purification and characterization of an α-L-arabinofuranosidase from Clostridium acetobutylicum ATCC 824

1 Department of Physics, National Tsing Hua University, Hsinchu 300044, Taiwan 2 Graduate Institute of Applied Physics and Department of Physics, National Taiwan University, Taipei 106216, Taiwan Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Strasse 40, 01187 Dresden, Germany 4 Department of Materials Science and Engineering, National Taiwan University, Taipei 106216, Taiwan 5 Materials Analysis Division, Taiwan Semiconductor Research Institute, National Applied Research Laboratories, Hsinchu 300091, Taiwan 6 National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan Institut für Ionenstrahlphysik und Materialforschung, Forschungszentrum DresdenRossendorf e.V., Bautzner Landstraße 128, 01328 Dresden, Germany 8 Institute of Physics, Academia Sinica, Taipei 11574, Taiwan

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Single-crystal epitaxial europium iron garnet films with strain-induced perpendicular magnetic anisotropy: Structural, strain, magnetic, and spin transport properties

S. F. Lee

Papers

Purification and characterization of an α-L-arabinofuranosidase from Clostridium acetobutylicum ATCC 824

Single-crystal epitaxial europium iron garnet films with strain-induced perpendicular magnetic anisotropy: Structural, strain, magnetic, and spin transport properties