Comparison of the aspartase activity and its stability in Escherichia coli cells immobilized on polyacrylamide gel and carrageenan

The conditions for immobilization of Escherichia coli cells (Soviet strain 85) on the natural polysaccharide carrier carrageenan (Soviet-made) were investigated and kinetic regularities of the aspartase reaction catalysed by immobilized in carrageenan cells of E. coli 85 were established. The conditions for retaining a high aspartase activity and stability of biocatalysts based on the E. coli 85 cells immobilized in PAAG and carrageenan were determined using full-loaded tanks for continuous synthesis of L-aspartic acid. The time-stable aspartase activity of the biocatalyst can be increased by treating the beads of the catalyst with bifunctional reagents (hexamethylenediamine, glutaraldehyde), the most active catalyst for the biotechnological synthesis of L-aspartic acid being obtained when carrageenan is used.     

Aspartase activity and the stability of Escherichia coli cells immobilized in different carrageenan samples

The cells of Escherichia coli 85 immobilized in carrageenan from various sources were being studied for the aspartase activity and stability. These properties of the resultant preparations which display a relatively high and stable biocatalytic activity were shown to be almost independent of the raw material from which carrageenan was obtained and of the degree of its purification.     

The influence of a specific microelemental environment in alginate gel beads on the course of propionic acid fermentation

In this work the exchange of calcium, cobalt, iron, magnesium, zinc and manganese ions between alginate gel beads and casein medium was investigated. The high release of calcium ions from alginate to the medium and the biosorption of some metal ions were observed. The pure alginate gel adsorbed all the metal ions examined, from a fermentative medium. Gel with immobilized cells of two strains of Propionibacterium freudenreichii subsp. shermanii showed an active ability to adsorb only cobalt, iron and zinc ions. In this way, a special microelemental environment was created in the alginate gel. This resulted in an increase of propionic acid production and a decrease of vitamin B₁₂ biosynthesis. Received: 30 April 1997 / Received revision: 2 July 1997 / Accepted: 4 July 1997     

Voltammetric study of the antioxidant activity of propionic acid bacteria in liquid cultures

For the first time, liquid cultures of Propionibacterium freudenreichii have been demonstrated to possess significant antioxidant activity. The direct and highly sensitive voltammetric method was applied which allowed for quantitative characterization of the cultures’ antioxidant activity through the calculated kinetic criterion.     

Continuous production of Emmental cheese flavours and propionic acid starters by immobilized cells of a propionic acid bacterium

Summary Characteristics of a continuous reactor with Propionibacterium cells entrapped with Ca-alginate are described. For a dilution rate D=0.45 h^–1, the gel produced 8 g.l^–1 for volatile fatty acids and 0.18 g.l^–1 for diacetylacetoin. The fiability of the process and its ability to produce propionic acid bacterium starter at the rate 4.10⁹ cells.l^–1 gel.h^–1 maked it attractive for industrial applications.     

Characteristics of the sulfate requirement of propionic acid bacteria

The kinetics of sulfate assimilation by Propionibacterium shermanii was found to be peculiar. The assimilation and excretion of sulfate into the medium had an oscillatory character. Sulfate was shown to pass into the cell by active transport. Sulfate transport is described by the Michaelis--Menten kinetics. Thiosulfate and sulfite inhibit sulfate assimilation. Cysteine does not entirely inhibit sulfate assimilation by the cells. The system of sulfate transport was repressed by cysteine to a small extent. The intracellular pool of inorganic sulfate changed in the process of culture growth.     

Superoxide radicals and antiradical defence of propionic acid bacteria

Superoxide dismutase activity was demonstrated for 6 strains of 3 propionibacteria species. Rather high level of superoxide dismutase activity found in propionibacteria was in accordance with high level of catalase activity reported for propionibacteria previously. Both these activities were shown to have cytozolic localization. For the first time peroxidase activity was detected in gel-fractionated crude cell extracts of propionibacteria. The ability to produce superoxide radicals in NADH-dependent oxidation system was revealed for three strains of the bacteria. The level of superoxide production by the membrane particles of the propionic acid bacteria correlated with the levels of superoxide dismutase and catalase activities and was the lowest for Propionibacterium shermanii. The ability to perform monovalent oxygen reduction during succinate oxidation was not revealed. The intact cells of P. globosum, P. vannielii, P. shermanii apparently did not excrete superoxide radicals into culture fluid during respiration.     

Synthesis of organic acids by immobilized propionic bacteria in the flow system and stabilization of the process

The capacity of immobilized cells of propionic bacteria to synthesize organic acids was examined. Propionibacterium shermanii cells incorporated into polyacrylamide gel were capable to synthesize propionic, acetic and pyruvic acids in the flow system. As a carbon source glucose, lactate-Na or whey lactose was used. The greatest amount of the acids was synthesized with the use of lactate-Na. The life-time of the biocatalyst (immobilized cells) can be increased by its reactivation with a nutrient medium required for optimal cell proliferation.     

Effect of ethanol addition on propionic acid consumption in an anaerobic bioreactor

Summary Experiments were carried out during the start up of an anaerobic bioreactor fed with synthetic medium based on glucose. Results showed different substrate fermentative pathways, mainly alcoholic fermentation and anaerobic oxidation. External ethanol additions produced a decrease in the levels of propionic acid. This method for stabilization of anaerobic reactors was more efficient than others reported in the literature.