Effect of toluene-permeabilization on oxidation of D-sorbitol to L-sorbose by Gluconobacter suboxydans cells immobilized in calcium alginate

Summary The effect of permeabilization of G. suboxydans cells with toluene on the oxidation of D-sorbitol to L-sorbose was investigated. Treatment of the cells with 10% toluene resulted in a three fold increase in the specific sorbitol dehydrogenase activity and a two fold increase in the efficiency of D-sorbitol conversion to L-sorbose of the free cell suspension. When the permeabilized cells were immobilized in calcium alginate, the operational stability during air-lift reactor operation was also found to increase with up to three times longer half-life(44 days) of catalytic activity compared with immobilized intact cells.     

Fed-batch cultivation of Acetobacter suboxydans for the microbial oxidation of D-sorbitol to L-sorbose

Microbial oxidation of D-sorbitol to L-sorbose is commercially important since it is the only biochemical process in Vitamin-C manufacture. The main bottleneck in the batch oxidation of D-sorbitol is that the process is severely inhibited by sorbitol. By conducting fed-batch fermentation, the inherent substrate inhibition present in batch fermentation can be eliminated. Batch fermentation with an initial sorbitol concentration of 200 g l^у featured a productivity of 14.2 g l^у h^у and a final sorbose concentration of 200 g l^у. Fed-batch fermentation conducted by feeding nutrients containing 600 g l^у of sorbitol at a constant feed rate of 0.36 l h^у yielded a productivity of 17.7 g l^у h^у and a final sorbose concentration of 320 g l^у.     

Conversion of L-sorbose to L-sorbosone by immobilized cells of Gluconobacter melanogenus IFO 3293.

Gluconobacter melanogenus IFO 3293 cells capable of converting L-sorbose to L-sorbosone were immobilized in polyacrylamide gel. The preferred polymer composition for high activity and stability was determined to contain a total monomer concentration of 7.2% and 16.6% crosslinking agent. No significant differences in optimal conditions for conversion, e.g., pH and temperature, were found in comparison with free cell suspensions. However, in the absence of L-sorbose, the thermal stability of immobilized cells was lower. After the initial loss, the conversion activity of immobilized cells increased, possibly due to lysis, and this increase was related to the polymerization conditions and the incubation temperature for the L-sorbose conversion. The enzymatic activity and stability of the immobilized cells also depended on the physical form of the gel and the aeration levels. Addition of electron acceptors or addition of L-sorbosone to the medium reduced, while addition of neomycin, ampicillin, chloramphenicol, and tetracycline increased the stability of the enzymatic activity.     

Glycerol production by cells of Saccharomyces cerevisiae immobilized in sintered glass

Summary Cells of Saccharomyces cerevisiae were immobilized in sintered glass Raschig rings for the production of glycerol. It can be shown that sintered glass with a porosity of 60% and pore dimensions of 60 to 100 m has a good adsorption capacity for cells of S. cerevisiae. This sintered glass was used in a fixed-bed loop reactor with a working volume of 81. Eight glycerol fermentations were carried out semicontinuously and led to glycerol yields of 26.2 to 29.5 g/l.     

NADPH-dependent L-sorbose reductase is responsible for L-sorbose assimilation in Gluconobacter suboxydans IFO 3291.

The NADPH-dependent L-sorbose reductase (SR) of L-sorbose-producing Gluconobacter suboxydans IFO 3291 contributes to intracellular L-sorbose assimilation. The gene disruptant showed no SR activity and did not assimilate the once-produced L-sorbose, indicating that the SR functions mainly as an L-sorbose-reducing enzyme in vivo and not as a D-sorbitol-oxidizing enzyme.     

Conversion of L-sorbose to L-sorbosone by Gluconobacter melanogenus

Growing cultures, washed cells, and cell-free extracts of Gluconobacter melanogenus IFO 3293 were found to convert L -sorbose to L -sorbosone. The product was identified by thin layer chromatography of the 2, 4-dinitrophenylhydrazone, and by paper partition chromatography using chemically prepared materials as standards. Factors influencing the conversion included incubation temperature and composition of the growth medium. Addition of betaine or choline to the growing cultures stimulated conversion of L -sorbose to L -sorbosone.