β-Xylanase production by Aureobasidium pullulans grown on sugars agricultural residues

Aureobasidium pullulans grew well in media containing glucose, fructose, xylan or xylose but -xylanase was only produced with xylan or xylose. Lactose and maltose were poor substrates for growth. -Xylanase production was repressed in media containing glucose or fructose along with xylose. Agricultural residues, such as wheat bran, paddy husk and rice straw, could be used as carbon sources for growth and -xylanase production of Aureobasidium pullulans. Tween 80 at 0.5% (v/v) increased the yield of -xylanase by up to 20%.     

In silico studies of plant primary cell walls – structure and mechanics

Primary plant cell wall (PCW) is a highly organized network, its performance is dependent on cellulose, hemicellulose and pectic polysaccharides, their properties, interactions and assemblies. Their mutual relationships and functions in the cell wall can be better understood by means of conceptual models of their higher-order structures. Knowledge unified in the form of a conceptual model allows predictions to be made about the properties and behaviour of the system under study. Ongoing research in this field has resulted in a number of conceptual models of the cell wall. However, due to the currently limited research methods, the community of cell wall researchers have not reached a consensus favouring one model over another. Herein we present yet another research technique – numerical modelling – which is capable of resolving this issue. Even at the current stage of development of numerical techniques, due to their complexity, the in silico reconstruction of PCW remains a challenge for computational simulations. However, some difficulties have been overcome, thereby making it possible to produce advanced approximations of PCW structure and mechanics. This review summarizes the results concerning the simulation of polysaccharide interactions in PCW with regard to network fine structure, supramolecular properties and polysaccharide binding affinity. The in silico mechanical models presented herein incorporate certain physical and biomechanical aspects of cell wall architecture for the purposes of undertaking critical testing to bring about advances in our understanding of the mechanisms controlling cells and limiting cell wall expansion.     

Effect of inoculum level on xylitol production from rice straw hemicellulose hydrolysate byCandida guilliermondii

The effect of inoculum level on xylitol production byCandida guilliermondii was evaluated in a rice straw hemicellulose hydrolysate. High initial cell density did not show a positive effect in this bioconversion since increasing the initial cell density from 0.67 g L^–1 to 2.41 g L^–1 decreased both the rate of xylose utilization and xylitol accumulation. The maximum xylitol yield (0.71 g g^–1) and volumetric productivity (0.56 g L^–1 h^–1) were reached with an inoculum level of 0.9 g L^–1. These results show that under appropriate inoculum conditions rice straw hemicellulose hydrolysate can be converted into xylitol by the yeastC. guilliermondii with efficiency values as high as 77% of the theoretical maximum.     

The influence of some natural cell-wall derived precursors on organogenesis and differentiation of wild strawberry (Fragaria vesca L.) callus cultures

Several kinds of precursors obtained by natural polymer hydrolysis of leaves, cell walls, cellulose and hemicelluloses have been tested on in vitro cultures. Interesting preliminary results were obtained with strawberry callus culture whereby all the tested hydrolysates were able to induce differentiation and organogenesis without addition of any plant growth regulators to the culture medium. This suggests the existence of one or more compounds, enzymatically released from the cell wall, which play a role on plant differentiation and organogenesis.Abbreviations AH agar hydrolysate - BA 6-benzyladenine - CH cotton hydrolysate - 2.4-d 2.4-dichlorophenoxyacetic acid - LH leaf hydrolysate - MS Murashige & Skoog medium - NAA -naphthalene-acetic acid - WH cell wall hydrolysate     

Staining reactions for the detection of hemicellulose-degrading bacteria

Abstract The use of dye-polysaccharide interactions in visualizing zones of polymer hydrolysis has been used to facilitate the detection of hemicellulolytic activity. Grams iodine was particularly effective in confirming the degradation of hemicellulosic pentosans and some α-glucans, whereas Congo Red and Trypan Blue interacted strongly with the β- d -glucans tested. Organisms, selectively isolated from garden compost, that produced iodinevisualized zones of hydrolysis all possessed xylanase activity; this enzyme was not detected in the isolates that failed to produce hydrolysis zones. Post-incubation staining with Grams iodine will therefore expedite the detection and unambiguous enumeration of hemicellulolytic isolates on enrichment culture.     

Production of yeast SCP from corn stover hydrolysates

The relative ease with which the hemicellulose component present in agricultural residues are hydrolyzed makes these raw materials attractive sources of sugars for the production of SCP. Corn stover has been selected for this study as a representative of a wide variety of crop residues of potential interest. The hydrolysates obtained by treating this material with dilute acid solutions were supplemented with non-carbon nutrients and the mixture of pentoses and hexoses converted into yeast biomass by a strain of Candida utilis in submerged cultivation. To be economically attractive mild hydrolysis conditions were considered although incomplete hydrolysis to monosaccharides were obtained. The performance of the fermentation has been studied in batch as well as in continuous systems. High efficiency of substrate utilization and protein productivity were obtained with a special yeast strain (CMI-23311) compared to the one (ATCC-9226) commonly studied as SCP source.     

An arabinogalacto(4-O-methylglucurono)xylan from the leaves of Hordeum vulgare

An arabinogalacto(4-O-methylglucurono)xylan with a $\text{DP}$_n of ca. 96 has been isolated from the leaves of barley. Based on structural studies it is proposed that the hemicellulose consists of a main chain of β (1→4)-linked d-xylopyranosyl residues to which are attached an average of 8·1 l-arabinofuranosyl residues, 3·8 galactopyranosyl-(1→4)-d-xylopyranosyl-(1→2)-l-arabinofuranosyl residues and 4·4 4-O-methyl-d-glucopyranuronosyl residues.     

Comparative Histochemical Analysis of Cell Wall Polysaccharides by Enzymatic and Chemical Extractions of Two Fruits

A protocol for extracting polysaccharides from cell walls has been modified and used to analyze histochemically two fruits with opposite characteristics. Grapes are nonclimacteric fruits and are harvested at full maturity. In contrast, kiwi fruits are climacteric and are harvested and consumed before they are physiologically mature. The two fruits were analyzed histochemically using two protocols. One method is defined as chemical, and is based on subsequential extractions of pectins by chemical agents. The other is defined as enzymatic because it removes pectins using pectinase followed by hot ammonium oxalate. In both protocols, two types of hemicellulosic polymers are removed by 1 M and 4 M/KOH leaving a cellulosic residue on the slide. Both protocols remove the same amount of pectins, thus confirming their precision. The sum of hemicellulose and the cellulosic insoluble residue are equivalent using the two methods, but the relative amounts of the cellulose and hemicellulosic polymers were dependent upon the method of extraction. When the enzyme was used to extract the pectins, there was less cellulose and more hemicellulose. The removal of polysaccharides by ammonium oxalate and by guanidinethio-cyanate in the enzymatic and the chemical protocols, respectively, yielded approximately the same amount of removed material.

Similar results were obtained from both fruits. Grape, being softer than kiwi fruit, was relatively richer in pectic substances and less rich in hemicellulose and cellulose polymers. No difference in cell wall material could be ascribed to the different ripening habits.     

Structural,mutagenic and in silico studies of xyloglucan fucosylation in Arabidopsis thaliana suggest a water‐mediated mechanism

The mechanistic underpinnings of the complex process of plant polysaccharide biosynthesis are poorly understood, largely because of the resistance of glycosyltransferase (GT) enzymes to structural characterization. In Arabidopsis thaliana, a glycosyl transferase family 37 (GT37) fucosyltransferase 1 (AtFUT1) catalyzes the regiospecific transfer of terminal 1,2‐fucosyl residues to xyloglucan side chains – a key step in the biosynthesis of fucosylated sidechains of galactoxyloglucan. We unravel the mechanistic basis for fucosylation by AtFUT1 with a multipronged approach involving protein expression, X‐ray crystallography, mutagenesis experiments and molecular simulations. Mammalian cell culture expressions enable the sufficient production of the enzyme for X‐ray crystallography, which reveals the structural architecture of AtFUT1 in complex with bound donor and acceptor substrate analogs. The lack of an appropriately positioned active site residue as a catalytic base leads us to propose an atypical water‐mediated fucosylation mechanism facilitated by an H‐bonded network, which is corroborated by mutagenesis experiments as well as detailed atomistic simulations.     

Fermentation of sugar cane bagasse hemicellulosic hydrolysate and sugar mixtures to ethanol by recombinant Escherichia coli KO11

Escherichia coli KO11, carrying the ethanol pathway genes pdc (pyruvate decarboxylase) and adh (alcohol dehydrogenase) from Zymomonas mobilis integrated into its chromosome, has the ability to metabolize pentoses and hexoses to ethanol, both in synthetic medium and in hemicellulosic hydrolysates. In the fermentation of sugar mixtures simulating hemicellulose hydrolysate sugar composition (10.0 g of glucose/l and 40.0 g of xylose/l) and supplemented with tryptone and yeast extract, recombinant bacteria produced 24.58 g of ethanol/l, equivalent to 96.4% of the maximum theoretical yield. Corn steep powder (CSP), a byproduct of the corn starch-processing industry, was used to replace tryptone and yeast extract. At a concentration of 12.5 g/l, it was able to support the fermentation of glucose (80.0 g/l) to ethanol, with both ethanol yield and volumetric productivity comparable to those obtained with fermentation media containing tryptone and yeast extract. Hemicellulose hydrolysate of sugar cane bagasse supplemented with tryptone and yeast extract was also readily fermented to ethanol within 48 h, and ethanol yield achieved 91.5% of the theoretical maximum conversion efficiency. However, fermentation of bagasse hydrolysate supplemented with 12.5 g of CSP/l took twice as long to complete. This revised version was published online in November 2006 with corrections to the Cover Date.