Henry R. Bungay

Microbial interactions in continuous culture.

Publisher Summary Mixed culture phenomena are not merely composites of the pure culture behavior of the organisms present. The performance of a complex microbial process depends on interactions between its species and strains. Microorganisms have vastly different nutritional requirements. They exhibit a wide range of growth rates and thrive at various conditions of pH, temperature, ionic strength, and the like. In spite of this diversity, species persist in nature throughout times of hardship and can flourish when favorable conditions occur. Thus the occurrence of unusual physical or chemical conditions or of rare nutritional circumstances leads to population changes in which different species achieve predominance so that relatively efficient microbial processes can continue. This adaptability of mixed populations is a key to the study of the microbiology of natural environments. Understanding of the mechanisms underlying this adaptation must come from investigations of population dynamics and microbial interactions.

Recent progress in bioconversion of lignocellulosics

D.B. Wilson, D.C. Irwin: Genetics and Properties of Cellulases.- N.S. Mosier, P. Hall, C.M. Ladisch, M.R. Ladisch: Reaction Kinetics, Molecular Action, and Mechanisms of Cellulolytic Proteins.- J.S. Tolan, B. Foody: Cellulase from Submerged Fermentation.- P. Cen, L. Xia: Production of Cellulase by Solid-State Fermentation.- Y.Y. Lee, P. Iyer, R.W. Torget: Dilute-Acid Hydrolysis of Lignocellulosic Biomass.- T.W. Jeffries, N.-Q. Shi: Genetic Engineering for Improved Xylose Fermentation by Yeasts.- N.W.Y. Ho, Z. Chen, A.P. Brainard, M. Sedlak: Successful Design and Development of Genetically Engineered Saccharomyces Yeasts for Effective Cofermentation of Glucose and Xylose from Cellulosic Biomass to Fuel Ethanol.- H.M. Muhlemann, H.R. Bungay: Research Perspectives for Bioconversion of Scrap Paper. C.S. Gong, N.J. Cao, J. Du, G.T. Tsao: Ethanol Production from Renewable Resources.- G.T. Tsao, N.J. Cao, J. Du, C.S. Gong: Production of Multifunctional Organic Acids from Renewable Resources.

Composites of bacterial cellulose and paper made with a rotating disk bioreactor

Suspended solids in the nutrient medium for Acetobacter xylinium in a rotating disk bioreactor become incorporated into the gelatinous mat of bacterial cellulose as it forms. Embedding fibers of ordinary cellulose creates composites with enhanced strength and the toughness of bacterial cellulose. Purified cellulose and elongated fibers from paper are incorporated differently than are spherical particles such as silica gel. About 90% of the final cellulose can come from scrap paper, and dried composite sheets were much stronger than plain bacterial cellulose per unit area.

Recycle of the cellulase-enzyme complex after hydrolysis of steam-exploded wood

Cellulases can be recovered in high yields by contacting fresh substrate with hydrolysis filtrate and by extraction of spent hydrolysis residue with pH 7 buffer. Recycled enzymes give hydrolysis rates about equal to those with fresh enzymes. Steam-exploded wood (SEW) is washed with water to remove sugars and byproducts from breakdown of hemicellulose, and recycle of enzymes proceeds better if lignin is also removed prior to hydrolysis. Oven drying of SEW interferes with recycle, and the recovery of enzymes is only one-half of that with SEW that is kept moist.Effectiveness of enzyme recovery depends on the completeness of hydrolysis, as determined by contact time and enzyme concentration. For cost-effective operation, enzyme should not be recovered until appreciable filter paper activity and carboxylmethylcellulase activity appear in the hydrolysate.

Inhibition of cellulases by impurities in Steam-Exploded wood.

Steam explosion of hardwood chips produces impurities that reduce the activity and stability of cellulases. Washing the exploded wood with water removes the inhibitors and permits hydrolysis equivalent to that with purified cellulose.

Continuous culture, feedback control and auxostats

Abstract Improved sensing methods and computerized control of bioreactors are encouraging the development of auxostats, continuous culture systems in which, unlike the chemostat, the growth rate (dilution rate) can vary. Auxostats are useful, in particular, for studying cultures growing at rates close to their maxima and they can be used to select fast-growing cultures. Although development is at an early stage, it is clear that, in order to operate commercially, auxostats would probably require some form of effluent recycle or multistage reactor configuration.

Model for microbial growth with more than one limiting nutrient

Abstract Microbial growth rate is determined by concentrations of nutrients. Our new model uses conventional Monod formulations and weighs the contribution of potentially limiting nutrients according to their half-saturation constants. The model fits our data and that of others better than do older models, even though no new coefficients were added.

Recovery of enzymes from the insoluble residue of hydrolyzed wood

During the enzymatic hydrolysis of steam-exploded wood, enzymes are adsorbed on both the cellulosic and noncellulosic components. Significant amounts of enzymes are recovered from the spent hydrolysis residue, which consists mostly of lignin, by neutralizing the pH from 4.5, the optimum for hydrolysis.

Growth of Yeast Colonies on Solid Media

Colonies on nutrient agar of the aerobic yeast Candida utilis show linear increases in diameter and height with time throughout most of the growth cycle. The concentration of glucose in the agar has a negligible effect on radial growth rate although an increase in the glucose concentration prolongs the linear radial growth phase. The rate of increase in height of the colony is proportional to the square root of the initial glucose concentration. A new model that considers both glucose diffusion and oxygen diffusion in the colony is consistent with the observed colony profiles.

Regulation of oxidoreductive yeast metabolism by extracellular factors

Abstract Since antiquity man has consumed ethanol produced by yeast as sugars are metabolized. Industrial alcohol and alcoholic beverages play major roles in our economy. Although the processes have been anaerobic except for the beneficial introduction of a trace of air or oxygen, the focus may shift to a novel approach to yeast bioprocessing using recent understanding of the aerobic ethanol production. In this minireview, we address glycolysis, oxidoreductive metabolism, and ion transport in yeast, and we introduce high-rate bioprocess control strategies that hinge on the effects of ionic composition. Consideration of maintenance requirements for glycolysis leads to an assessment of the role of monitoring and control of ionic concentrations for optimization of ethanol production.