1.0. Introduction 4044 2.0. Biomass Chemistry and Growth Rates 4047 2.1. Lignocellulose and Starch-Based Plants 4047 2.2. Triglyceride-Producing Plants 4049 2.3. Algae 4050 2.4. Terpenes and Rubber-Producing Plants 4052 3.0. Biomass Gasification 4052 3.1. Gasification Chemistry 4052 3.2. Gasification Reactors 4054 3.3. Supercritical Gasification 4054 3.4. Solar Gasification 4055 3.5. Gas Conditioning 4055 4.0. Syn-Gas Utilization 4056 4.1. Hydrogen Production by Water−Gas Shift Reaction 4056

/pdf/synthesis-of-transportation-fuels-from-biomass-chemistry-3sckhzoqoz.pdf

Synthesis of transportation fuels from biomass: chemistry, catalysts, and engineering.

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

Features of promising technologies for pretreatment of lignocellulosic biomass.

Fundamental features of microbial cellulose utilization are examined at successively higher levels of aggregation encompassing the structure and composition of cellulosic biomass, taxonomic diversity, cellulase enzyme systems, molecular biology of cellulase enzymes, physiology of cellulolytic microorganisms, ecological aspects of cellulase-degrading communities, and rate-limiting factors in nature. The methodological basis for studying microbial cellulose utilization is considered relative to quantification of cells and enzymes in the presence of solid substrates as well as apparatus and analysis for cellulose-grown continuous cultures. Quantitative description of cellulose hydrolysis is addressed with respect to adsorption of cellulase enzymes, rates of enzymatic hydrolysis, bioenergetics of microbial cellulose utilization, kinetics of microbial cellulose utilization, and contrasting features compared to soluble substrate kinetics. A biological perspective on processing cellulosic biomass is presented, including features of pretreated substrates and alternative process configurations. Organism development is considered for "consolidated bioprocessing" (CBP), in which the production of cellulolytic enzymes, hydrolysis of biomass, and fermentation of resulting sugars to desired products occur in one step. Two organism development strategies for CBP are examined: (i) improve product yield and tolerance in microorganisms able to utilize cellulose, or (ii) express a heterologous system for cellulose hydrolysis and utilization in microorganisms that exhibit high product yield and tolerance. A concluding discussion identifies unresolved issues pertaining to microbial cellulose utilization, suggests approaches by which such issues might be resolved, and contrasts a microbially oriented cellulose hydrolysis paradigm to the more conventional enzymatically oriented paradigm in both fundamental and applied contexts.

/pdf/microbial-cellulose-utilization-fundamentals-and-4yec12qx1c.pdf

Microbial cellulose utilization: fundamentals and biotechnology.

Pretreatments to enhance the digestibility of lignocellulosic biomass

Pretreatment technologies for an efficient bioethanol production process based on enzymatic hydrolysis: A review

Bacillus subtilis C-756, a producer of cyclic adenosine 3′,5′-monophosphate (cAMP) phosphodiesterase inhibitor, was cultured in media adjusted to various water activity (aw) levels by addition of three different solutes, sodium chloride, ethylene glycol and polyethylene glycol 1540 (PEG).

Effect of water activity on the growth and the production of cAMP phosphodiesterase inhibitor with Bacillus subtilis

The current interest in utilizing carbohydrates as raw materials for producing chemicals and fuels via various fermentation routes has focused interest on cheap and efficient hydrolysis processes for the production of fermentable sugars. The hydrolysis of cellulose, especially, has received much attention, since cellulose is the most abundant source of renewable carbohydrates.' The present technology essentially offers two ways for cellulose hydrolysis: acid and enzymatic. The former is fast but has the drawback of low yields. Furthermore, the corrosion problem has not yet been fully solved. The latter can give theoretical yields, but is slow and subject to severe product inhibition, particularly when the intermediate cellobiose accumulates. This paper evaluates a third possibility: the utilization of solid superacids, perfluorinated resin-sulfonic acid catalysts, NAFIONR 501, generously supplied by E. I. du Pont de Nemours & Company, Wilmington, DE. Solid superacids have been successfully utilized in a number of reactions such as alkylations2 and esterifi~ations.~ Their utilization in hydrolysis resembles an acid hydrolysis. but the fact that they are solid makes it possible to remove them as well as to operate the hydrolysis process continuously in a plug-flow-type reactor. The hydrolysis of cellulose, starch, and cellobiose were first compared in a batch reaction (FIG. 1). The production of glucose from cellobiose and starch followed zero-order kinetics. No tendency for product inhibition was observed. However, cellulose was barely hydrolyzed. The difference in the results between starch and cellulose is probably due to the fact that starch is gelatinized a t the experimental temperature used, 9SoC, thus opening up the molecules to the catalyst more than for cellulose. In this way, steric hindrances imposed by both substrate and catalyst appear to prevent the hydrolysis of cellulose with solid superacids. The manufacturer recommends that the solid superacids be used in the presence of sodium chloride in order to enhance the reaction rate. In repeated batch hydrolysis experiments, it was found that the presence of sodium chloride released hydrogen ions into the medium, the effect being that the superacids lost their catalytic activity after

Solid Superacids for Hydrolyzing Oligo‐ and Polysaccharidesa

The purpose of this study was to help lay the foundation for further development of xylose-fermentingSaccharomyces cerevisiae yeast strains through an approach that combined metabolic engineering and random mutagenesis in a recombinant haploid strain that overexpressed only two genes of the xylose pathway. Previously,S. cerevisiae strains, overexpressing heterologous genes encoding xylose reductase, xylitol dehydrogenase and the endogenousXKS1 xylulokinase gene, were randomly mutagenised to develop improved xylose-fermenting strains. In this study, two gene cassettes (ADH1
 p
 -PsXYL1-ADH1
 T
 andPGK1
 p
 -PsXYL2-PGK1
 T
 ) containing the xylose reductase (PsXYL1) and xylitol dehydrogenase (PsXYL2) genes from the xylose-fermenting yeast,Pichia stipitis, were integrated into the genome of a haploidS. cerevisiae strain (CEN.PK 2-1D). The resulting recombinant strain (YUSM 1001) over-expressing theP. stipitis XYL1 andXYL2 genes (but not the endogenousXKS1 gene) was subjected to ethyl methane sulfonate (EMS) mutagenesis. The resulting mutants were screened for faster growth rates on an agar medium containing xylose as the sole carbon source. A mutant strain (designated Y-X) that showed 20-fold faster growth in xylose medium in shake-flask cultures was isolated and characterised. In anaerobic batch fermentation, the Y-X mutant strain consumed 2.5-times more xylose than the YUSM 1001 parental strain and also produced more ethanol and glycerol. The xylitol yield from the mutant strain was lower than that from the parental strain, which did not produce glycerol and ethanol from xylose. The mutant also showed a 50% reduction in glucose consumption rate. Transcript levels ofXYL1, XYL2 andXKS1 and theGPD2 glycerol 3-phosphate dehydrogenase gene from the two strains were compared with real-time reverse transcription polymerase chain reaction (RT-PCR) analysis. The mutant showed 10–40 times higher relative expression of these four genes, which corresponded with either the higher activities of their encoded enzymes or by-product formation during fermentation. Furthermore, no mutations were observed in the mutant’s promoter sequences or the open reading frames of some of its key genes involved in carbon catabolite repression, glycerol production and redox balancing. The data suggest that the enhancement of the xylose fermentation properties of the Y-X mutant was made possible by increased expression of the xylose pathway genes, especially theXKS1 xylulokinase gene.

Development and characterisation of a recombinant Saccharomyces cerevisiae mutant strain with enhanced xylose fermentation properties

Bioethanol is an alternative to fossil transportation fuel. It is produced from sugar- and starch-containing crops but current efforts have turned to ethanol from agricultural and forestry waste. These materials are not expected to compete with food and feed production and net emission of carbon dioxide is lower. Several ethanol-producing microorganisms have been assessed at laboratory scale, including Gram-positive and Gram-negative bacteria, eukaryotes such as yeasts and filamentous fungi, but few have so far been used at industrial scale. In this article, the advantages and disadvantages of the different microorganisms including co-cultures are discussed with respect to ethanol production from lignocellulose raw materials. The complexity of lignocellulose materials may require development of different microorganisms for different applications, so that 'tailor-made' strains for different lignocellulose raw materials may be more efficient than one 'super-microorganism' for any raw material.

A Microbial Perspective on Ethanolic Lignocellulose Fermentation

One problem in the utilization of lignocellulosic biomass for the production of liquid fuels such as ethanol is the fermentation of the hydrolyzed pentosan fraction, which can constitute as much as 37% of the raw material‘ and is composed mainly of the pentose, xylose. Several solutions for this problem have been suggested: the enzymatic conversion of xylose to xylulose followed by fermentation with Succharomyces cerevisiae,2 the use of thermophilic anaerobic bacteria such as Thermoanaerobacter ethanolicus’ which can directly ferment xylose to ethanol, or the use of several yeast strains, for example, Cundidu tropicalis, which under “semiaerobic” conditions are also capable of carrying out this p r o c e ~ s . ~ Each of these routes, however, has a flaw of one kind or another. For example, xylose isomerase is of bacterial origin and has a pH and temperature optimum different from yeast, making a one-step process difficult. T. ethanolicus is substrate-inhibited, resulting in product concentrations too low for economical use. Finally, the xylose-fermenting yeasts tend to produce xylitol as a major by-product, thus not utilizing xylose efficiently. This paper deals with the latter problem. Using Candida tropicalis ATCC 321 13 (generously supplied by AC Biotechnics, Arlov, Sweden), an attempt was made to shift product formation from xylitol to ethanol by altering aeration levels, with the use of the respiratory inhibitor, azide, and by decreasing the water activity in the medium. “Semiaerobic” (or oxygen-limited) conditions have been found to enhance ethanol production from xylose in some yeast strains.’ However, xylitol production is also enhanced in an oxygen-limited culture.6 Azide has previously been shown to enhance ethanol production in S. cerevisiue’ and the same was observed with a decreased water activity.* TABLE 1 summarizes the results with C. tropicalis. In agreement with previous reports, the yield of ethanol is highest under “semiaerobic” conditions, 50% higher than under aerobic conditions. However, the xylitol production increases as well under these conditions. The semiaerobic conditions were chosen for further experiments with azide and with decreased water activities because C. tropicalis functions poorly anaerobically (little or no growth and poor utilization of xylose). Azide was tested at two concentrations. 0.2 m M and 4.6 m M (TABLE 1). At the higher concentration, cell growth was inhibited and only 30% of the available xylose

Bärbel Hahn-Hägerdal

Papers

Effect of water activity on the growth and the production of cAMP phosphodiesterase inhibitor with Bacillus subtilis

Solid Superacids for Hydrolyzing Oligo‐ and Polysaccharidesa

Development and characterisation of a recombinant Saccharomyces cerevisiae mutant strain with enhanced xylose fermentation properties

A Microbial Perspective on Ethanolic Lignocellulose Fermentation

Shifting Product Formation from Xylitol to Ethanol in Pentose Fermentation with Candida tropicalis by Alteringa