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.

Acetone-butanol fermentation revisited.

Plant cell cultures: Chemical factories of secondary metabolites

Deactivation of heterogeneous catalysts is a ubiquitous problem that causes loss of catalytic rate with time. This review on deactivation and regeneration of heterogeneous catalysts classifies deactivation by type (chemical, thermal, and mechanical) and by mechanism (poisoning, fouling, thermal degradation, vapor formation, vapor-solid and solid-solid reactions, and attrition/crushing). The key features and considerations for each of these deactivation types is reviewed in detail with reference to the latest literature reports in these areas. Two case studies on the deactivation mechanisms of catalysts used for cobalt Fischer-Tropsch and selective catalytic reduction are considered to provide additional depth in the topics of sintering, coking, poisoning, and fouling. Regeneration considerations and options are also briefly discussed for each deactivation mechanism.

/pdf/heterogeneous-catalyst-deactivation-and-regeneration-a-166g7jwbkh.pdf

Heterogeneous Catalyst Deactivation and Regeneration: A Review

Culture parameters influencing metabolism of synthetic14C-lignins to14CO2 in defined media have been studied in shallow batch cultures of the ligninolytic wood-destroying HymenomycetePhanerochaete chrysosporium Burds. Study of the effect of O2 concentration in the gas phase above non-agitated cultures indicated essentially complete absence of attack on the lignin polymer at 5% O2 in N2, and a 2- to 3-fold enhancement by 100% O2 as compared to air (21% O2). Agitation of the cultures resulting in the formation of mycelial pellets greatly suppressed lignin decomposition. The optimum culture pH for lignin decomposition was 4 to 4.5, with marked suppression above 5.5 and below 3.5. The source of nutrient nitrogen (NO
 3
 −
 , NH
 4
 +
 , amino acids) had little influence on lignin decomposition, but the concentration of nitrogen was critical; decomposition at 24 mM was only 25–35% of that at 2.4 mM N. Thiamine was the only vitamin required for growth and lignin decomposition. Under the optimum conditions developed, decomposition of 5 mg of synthetic lignin was accompanied by utilization of approximately 100 mg of glucose. The influence of the various culture parameters was analogous for metabolism of synthetic lignin labeled in the ring-,side chain-, and methoxyl carbon atoms.

Influence of culture parameters on lignin metabolism by Phanerochaete chrysosporium

The effect of intraparticle diffusion in artificial membranes on the kinetic behavior of immobilized enzymes has been considered theoretically in terms of an effectiveness factor. When the immobilized enxymes obey a Michaelis-Menten relationship, an approximate equation is proposed for the effectiveness factor. For a substrate inhibited enzymatic reaction, the effectiveness factor may exceed unity and display multiple steady-state behavior. Thus, the over-all rate of reaction in the artificial membrane is faster in this case than that when the substrate concentration in the interior is at the same as that at the exterior surface. In the case of a product inhibited enzymatic reaction, the effectiveness factor is always less than that which corresponds to a Michaelis-Menten relationship.



On a etudie theoriquement, en fonction d'un facteur d'efficacite, l'effet que produit la diffusion entre particules dans les membranes artificielles sur le comportement cinetique d'enzymes immobilisees. Lorsque les enzymes immobilisees obeissent a une relation de Michaelis et Menten, on propose une equation d'approximation pour le facteur d'efficacite. Dans le cas d'une reaction enzymatique inhibee par le substrat, le facteur d'efficacite peut ětre plus grand que 1 et indiquer un comportement de regimes permanents multiples; aussi, la vitesse globale de reaction dans la membrane artificielle est-elle plus considerable dans ce cas que lorsque la concentration du substrat a la surface interieure est la měme que celle qu'on note a la surface exterieure. Dans le cas d'une reaction enzymatique inhibee par un produit, le facteur d'efficacite est toujours moindre que celui qui correspond a une relation de Michaelis et Menten.

Effectiveness factors for immobilized-enzyme reactions

The oxygen uptake rate in mycelial pellets of Aspergillus niger was studied experimentally and theoretically. The specific rate of respiration of mycelial pellets was found to decrease significantly with increasing pellet size. The distribution of respiratory activity in the mycelial pellets was evaluated and the specific rate of respiration of disrupted mycelia showed adaptation to the concentration of oxygen in the medium. The decrease of the specific rate of respiration of the mycelial pellets could be estimated according to diameter, mycelial density, oxygen diffusivity, and adaptation to the concentration of oxygen. Good agreement was found between the theoretical analysis and the experimental data.

Oxygen transfer into mycelial pellets

Escherichia coli and Candida brassicae were cultivated in a fed-batch culture with a DO-stat under the condition that none of the components in the basal medium limited the growth of the microorganism. High densities of biomasses (125 g/l for E. coli and 138 g/l for C. brassicae) were obtained. The final biomasses obtained in the cultivations of E. coli and C. brassicae corresponded to 57% and 51%, respectively, of the limits that the organisms can be cultivated in view of viscosity of the broth. Metabolic products in the supernatant of the broth at the end of the cultivation and concentration of carbon dioxide in exit gas from the fermentor were measured, and the relations between cell concentration and growth yield with respect to carbon source were shown. It was considered that the decreases in growth yield and specific growth rate in the case of E. coli were due to the metabolites, including CO2, which increased to inhibitory concentrations. On the other hand, the possibility of obtaining a higher density of biomass was shown in the case of C. brassicae if a fermentor with higher oxygen transfer rate were used. Merits of using pure oxygen gas for production of biomass were exemplified.

https://www.jstage.jst.go.jp/article/jcej1968/12/4/12_4_313/_pdf

High density cultivation of biomass in fed-batch system with do-stat

Plant hairy roots from horseradish, carrots, etc. transformed by the soil bacterium Agrobacterium rhizogenes showed active growth in the phytohormone-free Murashige–Skoog medium with sucrose as a carbon source. Reticulate polyurethane foam was an appropriate support for the immobilization of hairy root cells. The hairy roots of 11 kg-dry cells·m–3 (110 kg-fresh cells·m–3) were obtained in a 31-d culture in an air-lift column bioreactor with immobilized horseradish cells. A linear relationship was observed between the dry cell mass grown and medium conductivity decrease for hairy root cultures. Thus, it was possible to monitor cell mass concentration during the hairy root culture by on-line measurement of conductivity in the bioreactor system.

Growth Characteristics of Plant Hairy Roots and Their Cultures in Bioreactors

An extractive fermentation system was developed to prevent end-product inhibition of Clostridium acetobutylicum I AM 19012, which mainly produces butanol and acetone. Butanol exhibited greater toxicity to the microorganism than acetone, and its growth was completely inhibited above 10kg/m3 of butanol. As an extracting solvent suitable for acetone-butanol fermentation, oleyl alcohol (cis-9-octadecen-l-ol) and C-20 guerbet alcohol (branched-chain alcohol of carbon number, 20) were selected from among 29 organic compounds, based on their nontoxicity to the microorganism. These two solvents had high partition coefficients for butanol, and could be reused without deterioration. In fermentation with the solvent (solvent phase: aqueous phase = 2:5 (v/v)), the viability of the microorganism was resumed by the liquid-liquid extraction of butanol from the broth, and the amount of butanol produced was 2.6 times that in fermentation without extraction.

https://www.jstage.jst.go.jp/article/jcej1968/18/2/18_2_125/_pdf

Takeshi Kobayashi

Papers

Effectiveness factors for immobilized-enzyme reactions

Oxygen transfer into mycelial pellets

High density cultivation of biomass in fed-batch system with do-stat

Growth Characteristics of Plant Hairy Roots and Their Cultures in Bioreactors

Production of butanol by clostridium acetobutylicum in extractive fermentation system