https://faculty.washington.edu/renatab/courses/PSE490/downloads/pretreatment.pdf

Features of promising technologies for pretreatment of lignocellulosic biomass.

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

A significant goal in the post-genome era is to relate the annotated genome sequence to the physiological functions of a cell. Working from the annotated genome sequence, as well as biochemical and physiological information, it is possible to reconstruct complete metabolic networks. Furthermore, computational methods have been developed to interpret and predict the optimal performance of a metabolic network under a range of growth conditions. We have tested the hypothesis that Escherichia coli uses its metabolism to grow at a maximal rate using the E. coli MG1655 metabolic reconstruction. Based on this hypothesis, we formulated experiments that describe the quantitative relationship between a primary carbon source (acetate or succinate) uptake rate, oxygen uptake rate, and maximal cellular growth rate. We found that the experimental data were consistent with the stated hypothesis, namely that the E. coli metabolic network is optimized to maximize growth under the experimental conditions considered. This study thus demonstrates how the combination of in silico and experimental biology can be used to obtain a quantitative genotype-phenotype relationship for metabolism in bacterial cells.

In silico predictions of Escherichia coli metabolic capabilities are consistent with experimental data

The Escherichia coli MG1655 genome has been completely sequenced. The annotated sequence, biochemical information, and other information were used to reconstruct the E. coli metabolic map. The stoichiometric coefficients for each metabolic enzyme in the E. coli metabolic map were assembled to construct a genome-specific stoichiometric matrix. The E. coli stoichiometric matrix was used to define the system's characteristics and the capabilities of E. coli metabolism. The effects of gene deletions in the central metabolic pathways on the ability of the in silico metabolic network to support growth were assessed, and the in silico predictions were compared with experimental observations. It was shown that based on stoichiometric and capacity constraints the in silico analysis was able to qualitatively predict the growth potential of mutant strains in 86% of the cases examined. Herein, it is demonstrated that the synthesis of in silico metabolic genotypes based on genomic, biochemical, and strain-specific information is possible, and that systems analysis methods are available to analyze and interpret the metabolic phenotype.

/pdf/the-escherichia-coli-mg1655-in-silico-metabolic-genotype-its-q3ay1kx2k5.pdf

The Escherichia coli MG1655 in silico metabolic genotype: Its definition, characteristics, and capabilities

Introduction. Cellular Growth Reactions. Analysis of Reaction Rates. Modelling of Reaction Kinetics. Morphologically Structured Models. Population Balances Based on Cell Number. Mass Transfer. Ideal Bioreactors. Bioreactor Modelling. Index.

Bioreaction Engineering Principles

Glucoamylase has been covalently immobilized in controlled pore glass fibers packed parallel to the axis of a tubular reactor. Flow kinetic studies have been carried out for a range of flow rates and substrate concentrations at 50°C and pH 4.5. Diffusion control has been found negligible with high flow rates and substrate concentrations. The apparent Michaelis constant was three orders of magnitude higher than that of the free enzyme. As flow rate and substrate concentration decrease, the extent of diffusion control increased up to a moderate degree. The immobilized glucoamylase was more stable than the free enzyme when incubated at 50°C.

Maltose hydrolysis kinetics with glucoamylase immobilized in porous glass fibers in a tubular flow reactor

An industrial by-product stream consisting primarily of α- and β-methyl xylosides supported microbial growth provided the treated syrup was diluted such that the osmotic pressure was within the range tolerated by the particular microorganism used. A culture screening study identified two organisms that efficiently utilized both α- and β-methyl xyloside. Xylose, α-, and β-methyl xylosides were all utilized simultaneously during batch growth ofArthrobacter sp. in a controlled-pH fermentor, although xylose was consumed faster than either xyloside. In addition,Arthrobacter sp. produced glucose isomerase when grown on the syrup.

Utilization of a wood-based syrup as a fermentation carbon source

A mathematical model based on the production and consumption of ATP is presented which attempts to simulate the batch fermentation kinetics of Klebsiella pneumoniae. The chief utility of the model is its apparent ability to predict the non-linear way the product yields vary during oxygen limited growth when two different energy producing pathways are active.

Norman B. Jansen

Papers

Maltose hydrolysis kinetics with glucoamylase immobilized in porous glass fibers in a tubular flow reactor

Utilization of a wood-based syrup as a fermentation carbon source

A model for the growth and product kinetics of facultative anaerobes based on atp synthesis and consumption