Monitoring of Saccharomyces cerevisiae in commercial bakers' yeast fermentation.

In the highly competitive market of commercial bakers' yeast, fermentations are operated for maximum efficiency and minimum production cost. In order to maintain competitiveness, the fermentations must be highly consistent with minimum variation in yeast performance, maximum yield on raw materials, and minimum production of undesirable side products. The use of advanced instrumentation is of critical importance to achieving these goals by the production engineer. An in situ optical density probe was used to determine the yeast cell density in full-scale commercial bakers' yeast fermentations. The optical density probe results were compared with oxygen uptake rate analyses, packed cell volume, and off-line measured cell dry weights. The most accurate measurement of cell density was found to be the optical density probe. This instrument allowed the on-line determination of cell density with highly consistent results from fermentation batch to batch and with out the need for intermittent recalibration. (c) 1995 John Wiley & Sons, Inc.

Wheezing, hypoxia, and dyspnea in a 62-year-old woman.

This patient presented with dyspnea, hypoxia, and generalized wheezing; however, her pulmonary function testing did not suggest asthma. Subsequent evaluations for conditions that may mimic asthma were not helpful. An invasive procedure (pulmonary angiogram) was required to diagnose pulmonary embolism, a potentially life threatening but treatable condition. The angiogram was performed despite nondiagnostic ventilation and perfusion scans because of a high index of suspicion for pulmonary embolism. In our patient, observation revealed episodes of sudden tachycardia, dyspnea, and increased wheezing which further raised our suspicion. Because pulmonary emboli can have such protean manifestations, it would be wise to consider pulmonary emboli in any patient with presumed asthma who has symptoms out of proportion to his or her pulmonary function testing and/or is not responding to treatment.

Treatment options in the child with a chronic cough.

Chronic cough is a common symptom in many different disease processes. Because the most effective way to eliminate a chronic cough is to identify and treat the underlying disease, the physician must approach the paediatric patient based on his or her knowledge of the differential diagnosis. The most common causes of cough in children are upper respiratory tract infections, asthma, rhinitis, sinusitis, and gastroesophageal reflux. By using a systematic approach, the cause of a chronic cough can almost always be found, and the cough successfully treated. Asthma is the cause of most undiagnosed chronic coughs but sinusitis, rhinitis, and gastroesophageal reflux must also be considered in difficult patients.

Control of Escherichia coli-Candida utilis continuous, competitive mixed-culture system using the dynamic matrix control algorithm.

The control of the continuous, competitive mixed culture of the yeast Candida utilis (ATCC 8205) and the bacterium Escherichia coli B/r (ATCC 12407) was examined. A modified version of the dynamic matrix control (DMC) algorithm was tested in simulation and then was successfully implemented. This represents the first report of the location and stabilization of a competitive mixed culture at a metastable equilibrium point using automatic control.

Fed-batch fermentation for the production of alpha-amylase by Bacillus amyloliquefaciens.

Fed-batch cultures were performed to maximize the alpha-amylase activity in a bioreactor. Kinetic equations containing a catabolite repression effect were used to model the enzyme formation from Bacillus amyloliquefaciens. Fed-batch culture experiments were performed using maltose to implement the optimal feeding strategy. Optimal fed-batch culture based on sequential parameter estimation was performed successfully using off-line analysis while the fermentation was in progress. The enzyme activity from the fed-batch culture employing maltose was higher than that of the batch culture by 60%. Enzyme production using starch showed similar trends to those obtained using maltose.

Kinetics of alpha-amylase synthesis from Bacillus amyloliquefaciens.

The microbial production of alpha-amylase from Bacillus amyloliquefaciens was investigated. The microorganism was grown using media containing glucose or maltose at 37 degrees C and under aerobic conditions in a 16-L fermentor. The alpha-amylase synthesis from maltose was not found to be inducible but was found to be subject to catabolite repression. The maltose uptake rate was observed to be the rate-limiting step compared to the conversion rate of maltose to glucose by intracellular alpha-glucosidase. The alpha-amylase activity achieved with maltose as a substrate was higher than that achieved with glucose. A slower growth rate and a higher cell density were obtained with maltose. The enzyme production pattern depended upon the nutrient composition of the medium.

Some observations on the role of type 1 fimbriae in Escherichia coli autoflocculation.

Techniques are reviewed for the identification and enrichment of fimbriae-positive and fimbriae-negative Escherichia coli. Fimbriae-positive E. coli were observed to form a semistable suspension of pH 7.0 which settled at a rate much slower than the fimbriae-negative bacteria. Intense autoflocculation of fimbriae-positive E. coli was noted at pH values below 5.2.

Evaluation of Escherichia coli and Candida utilis as a model continuous, competitive mixed culture system.

The yeast Candida utilis and the bacterium Escherichia coli B/r were evaluated as a candidate experimental, continous, competitive mixed culture system under ammonia-nitrogen limited conditions at 30 degrees C. High dilution rates favored yeast dominance, while low dilution rates favored bacterial dominance. The hydrogen ion concentration was also demonstrated to be an effective manipulative variable for control of the yeast-bacterial mixed culture. Through trial-and-error manipulation of the pH for the mixed culture operating at constant dilution rate, it was possible to locate a metastable equilibrium point and to operate in the vicinity of that point for more than 24h. The reproducible emergence of a variant E. coli was also noted in this study.

Experimental design for parameter estimation from batch culture.

An experimental design to estimate the parameters in a Monod-type equation from batch culture data was examined. Consideration was given to the design of experiments to estimate accurate values of the parameters. Sequential experimental design with the information index was used for this purpose. With this approach the standard deviation of the parameter values was reduced using simulated batch culture data.

The response of a nitrogen-limited chemostat culture of Escherichia coli B/r to pH and dilution rate steps.

The effects of four pH steps and one dilution rate step are described for an ammonia-nitrogen-limited continuous culture of Escherichia coli B/r. Two of the pH steps, 6.06-5.49 and 5.96-5.60, led to prolonged transients in both cell density and rate-limiting nutrient concentration. The other two pH steps, 6.20-5.96 and 5.60-6.20, had almost no effect on the culture. The dilution rate step led to a sharp transition in the steady-state external pyruvate concentration. Monitoring of the external pyruvate concentration for the pH 5.96-5.60 step revealed that the transient phase continued long after the cell density and rate-limiting nutrient concentration returned to steady-state values. The implications for industrial and laboratory fermentations are discussed.

Aerobic microbial growth in semisolid matrices: heat and mass transfer limitation.

A conceptual model of aerobic microbial growth in semisolid matrices were developed as a first step in the prediction of the rate of breakdown in semisolid cellulosic material. The conceptual model was described by a series of equations simplified by the assumption of steady-state microbial activity, and heat and mass transfer limitation. Temperature and oxygen distribution in compost piles were measured experimentally at the Butler County Mushroom Farm, Butler County, Pennsylvania, to test the validity of these assumptions. The compost piles consisted of ground corn husks, straw, and race horse manure. The data fit with the model was excellent with deviation between model predictions (as solved by an anglog computer) and actual temperature measurements never exceeding 3 degrees C. The effects of compost pile geometry, external temperature, compost density, external oxygen concentration, and insulation at the bottom of the pile were then predicted using a digital computer to solve the model. The predicitions show that the maximum breakdown rate occurs for an optimum height (which depends upon the system), insulating the base increases the breakdown rate, increasing the external temperature increases the initial breakdown rate but decreases the pseudo-steady-state breakdown rate and the uniformity and any increase in the external oxygen concentration increases the breakdown rate but decreases the uniformity.