Continuous production of extracellular protease by Bacillus subtilis in a two-stage fermentor

Continuous Production of Thermostable beta-Amylase with Clostridium thermosulfurogenes: Effect of Culture Conditions and Metabolite Levels on Enzyme Synthesis and Activity

A beta-amylase-overproducing mutant of Clostridium thermosulfurogenes was grown in continuous culture on soluble starch to produce thermostable beta-amylase. Enzyme productivity was reasonably stable over periods of weeks to months. The pH and temperature optima for beta-amylase production were pH 6.0 and 60 degrees C, respectively. Enzyme concentration was maximized by increasing biomass concentration by using high substrate concentrations and by maintaining a low growth rate. beta-Amylase concentration reached 90 U ml at a dilution rate of 0.07 h in a 3% starch medium. A further increase in enzyme activity levels was limited by acetic acid inhibition of growth and low beta-amylase productivity at low growth rates.

A parametric study ot protease production in batch and fed-batch cultures of Bacillus firmus

Proteolytic enzymes produced by Bacillus species find a wide variety of applications in brewing, detergent, food, and leather industries. Owing to significant differences normally observed in culture conditions promoting cell growth and those promoting production of metabolites such as enzymes, for increased efficacy of bioreactor operations it is essential to identify these sets of conditions (including medium formulation). This study is focused on formulation of a semidefined medium that substantially enhances synthesis and secretion of an alkaline protease in batch cultures of Bacillus firmus NRS 783, a known superior producer of this enzyme. The series of experiments conducted to identify culture conditions that lead to improved protease production also enables investigation of the regulatory effects of important culture parameters including pH, dissolved oxygen, and concentrations of nitrogen and phosphorous sources and yeast extract in the medium on cell growth, synthesis and secretion of protease, and production of two major nonbiomass products, viz., acetic acid and ethanol. Cell growth and formation of the three nonbiomass products are hampered significantly under nitrogen, phosphorous, or oxygen limitation, with the cells being unable to grow in an oxygen-free environment. Improvement in protease production is achieved with respect to each culture parameter, leading in the process to 80% enhancement in protease activity over that attained using media reported in the literature. Results of a few fed-batch experiments with constant feed rate, conducted to examine possible enhancement in protease production and to further investigate repression of protease synthesis by excess of the principal carbon and nitrogen sources, are also discussed. The detailed investigation of stimulatory and repressory effects of simple and complex nutrients on protease production and metabolism of Bacillus firmus conducted in this study will provide useful guidelines for design of bioreactors for production of protease and bulk chemicals by this bacterium.

Comparison of Bacillus subtilis and Serratia marcescens as protease producers under different operating conditions

Two microorganisms, Bacillus subtilis and Serratia marcescens, have been selected in order to assess their ability to produce proteases. First, their performances have been studied using three media providing different levels of the main nutrients (complex, semi-defined and defined). The optimal absolute production was obtained in the complex media, while maximum protease activity per cell weight appeared in defined medium for Bacillus and in semi-defined and complex media for Serratia. Then, the effects of applying different environmental conditions to the cells were studied. The two microorganisms were immobilised in calcium alginate beads, protease production by these systems was assessed in the previously tested culture media, and the performances in free and immobilized operating conditions were compared. The richest medium seemed to be the best one in terms of absolute protease production, although the use of semi-defined or defined media could be considered more appropriate, in order to minimise growth of cells leaked from the support, and therefore downstream processing cost. Productivity was slightly higher in free cultures than in immobilized cultures, and retention of enzyme within the alginate beads was detected in the latter, indicating the occurrence of diffusional limitations. In all the cases studied, Serratia marcescens appeared as a better protease producer than B. subtilis, in terms of absolute production. This fact could be related to the different cell growth levels observed for the two microorganisms.

The production of industrial enzymes

This paper reviews the essential features and current techniques used on an industrial scale in the preparation of partly purified or ‘bulk’ enzymes, as opposed to highly purified enzymes for analytical or diagnostic use, which are covered elsewhere in this volume. Industrial enzymes may be derived from a wide variety of plant, animal or microbial sources, although most production processes rely on the last of these. Microbial enzymes are either extracellular, such as the proteases and carbohydrates, which account for a large proportion of total sales, or intracellular, such as glucose oxidase. Intracellular enzymes usually remain associated with the cell and therefore have to be released, unless the microorganism itself is used as the catalyst. Although specific fermentation procedures adopted by manufacturers vary to a degree, there remain only two principal methods of cultivation, i.e. solid-state and submerged fermentation. Most microbial enzymes are produced by aerobic submerged fermentation, which allows greater control of growth factors than solid-state methods. The recovery and purification techniques discussed are typical of those used for fermentation enzymes, although they may be applied, generally, to most extraction and refining operations irrespective of whether the enzyme source is of plant, animal or microbial origin. In particular the following processes are covered; cell disruption, precipitation and solid-liquid separation including concentration by ultrafiltration. It is shown how, by using a combination of these techniques at different stages in the recovery process, it is possible to produce a complete range of product specifications.

Characterization of bacterial growth by means of flow microfluorometry

By means of flow microfluorometry, the protein and nucleic acid contents of individual bacterial cells may be measured at the rate of several thousand cells per second. Accumulation of such information over a few minutes yields the composition distribution of the microbial population. These distributions have been determined at different times during batch growth of Bactillus subtilis, and the results indicate that the variance of cell composition decreases as the population passes through the exponential into the stationary phase. The relative abundance of endospores and vegetative cells as well as the protein distributions of these subpopulations may be readily determined from flow microfluorometry data. Experimental access to such details of microbial population dynamics should foster improved understanding of cell growth, spore germination, and spore formation kinetics.