Yu Ryang Pyun

Effects of pH and Dissolved Oxygen on Cellulose Production by Acetobacter xylinum BRC5 in Agitated Culture

Acetobacter xylinum BRC5 was cultivated in a jar fermentor using glucose as the sole carbon source. Strain BRC5 oxidized almost all of the glucose to gluconic acid; thereafter, it biosynthesized cellulose by utilizing gluconic acid accumulated in the broth. The optimal pH for metabolizing glucose to gluconic acid was 4.0, while a pH of 5.5 was preferred for cell growth and cellulose production from the accumulated gluconic acid in the medium. Shifting the pH from 4.0 to 5.5 during the cellulose production phase in batch cultures improved cellulose production and reduced the total fermentation time, compared to batch cultures at constant pH. In constant fed-batch culture, 10 g/l of cellulose was obtained from 40 g/l of glucose, a yield which was approximately 2-fold higher than in batch culture with the same initial glucose concentration, even without control of the level of dissolved oxygen. The highest cellulose yield was obtained in fed-batch cultures in which the dissolved oxygen concentration was controlled at 10% saturation. Control of pH and dissolved oxygen to optimal levels was effective for improving the production rate and yield of cellulose, to achieve a high cellulose productivity of 0.3 g cellulose/l x h. Approximately 15 g/l of cellulose was considered to be the highest yield obtainable using conventional fermentors because the culture broth then became too viscous to allow satisfactory aeration.

Cellulose production by Acetobacter xylinum BRC5 under agitated condition

Abstract A potent cellulose producer, Acetobacter xylinum BRC5, was cultivated in shaking flasks and jar fermentors with glucose, fructose, sucrose and mixtures of these as carbon sources. It was confirmed that corn steep liquor (CSL) was cheap and a suitable organic nitrogen source for cellulose production by strain BRC5. When glucose was used as a sole carbon source, strain BRC5 oxidized almost all the glucose to gluconic acid, thereafter it biosynthesized cellulose by utilizing the gluconic acid accumulated in the broth under limited glucose conditions. Since strain BRC5 did not metabolize fructose to acid, the fermentation pattern of fructose was found to be typically growth associated with cellulose production. However, when glucose and fructose coexisted in the medium, strain BRC5 preferentially metabolized all the glucose to gluconic acid. Thereafter, it produced cellulose mainly by utilizing fructose. Overall cellulose productivity in a jar fermentor ranged from 0.071 to 0.086 g/ l /h.

OPTIMIZATION OF OPERATING CONDITIONS IN TUNNEL DRYING OF FOOD

ABSTRACT Food drying process in tunnel dryer was modeled from Keeys drying model and experimental drying curve, and optimized in operating conditions consisting of inlet air temperature, air recycle ratio and air flow rate. Radish was chosen as a typical food material to be dried, because it has a typical drying characteristics of food and quality indexes of ascorbic acid destruction and browning in the drying. Stricter quality retention constraint required higher energy consumption in minimizing the objective function of energy consumption under constraints of dried food quality. Optimization results of cocurrent and counter current tunnel drying showed higher inlet air temperature, lower recycle ratio and higher air flow rate with shorter total drying time. Compared with cocurrent operation counter current drying used lower air temperature, lower recycle ratio and lower air flow rate, and appeared to be more efficient in energy usage. Most of consumed energy was analyzed to be used for air heating and ...

Cloning, Sequencing, and Expression of UDP-Glucose Pyrophosphorylase Gene from Acetobacter xylinum BRC5

A UDP-glucose pyrophosphorylase (UGPase) gene from Acetobacter xylinum BRC5 has been cloned, sequenced, and expressed in Escherichia coli. The gene consists of 867 nucleotides and encodes a polypeptide of 289 amino acid residues with a calculated molecular mass of 31,493 Da. The amino acid sequences of the enzyme showed an 85.8% identity to those of an enzyme from A. xilinum ATCC 23768. A polyhistidine-UGPase fusion enzyme was expressed and purified from the transformed E. coli. The enzyme showed a 35,620-Da single protein band on SDS/PAGE and an about 160,000-Da protein band on 8-16% pore-gradient polyacrylamide gel, indicating the enzyme may be a tetramer or pentamer composed of four or five identical subunits. Kinetic analysis of the enzyme showed a typical Michaelis-Menten substrate saturation pattern, from which Km and Vmax were calculated to be 3.22 mM and 175.4 μmol•min-1•mg-1 for UDP-glucose and 0.24 mM and 69.4 μmol•min-1•mg-1 for PPi, respectively, required Mg2+ for maximal activity, and was inhibited by free pyrophosphate. Computer-aided comparison of the Acetobacter enzyme sequence with those of other bacterial enzymes found significant similarities among them and predicted that Lys84 is a catalytically important residue. Lys84 in the enzyme, which was also conserved in other bacterial enzyme sequences, was replaced by arginine or leucine. The K84R mutant enzyme was successfully expressed in E. coli and showed enzyme activity (63% of the wild-type enzyme activity), but K84L was not isolated in stable form. These results suggest that Lys84 is significant in not only catalysis but also maintenance of the active structure.

Biochemical characteristics of chitinase enzyme from Bacillus sp. of Kamojang Crater, Indonesia.

Chitinase and chitindeacetylase are enzymes capable of degrading chitin into chitooligomers and chitosan. The chitinases characterized and purified in this study were extracted from the acidophillic Bacillus sp. isolated from Kamojang Crater West Java Indonesia. When grown in liquid media containing colloidal chitin, the optimum chitinase activity of the acidophilic isolate was reached after 4-5 days of incubation. The optimum temperature and pH of the chitinase and chitin deacetylase were found at 37 degrees C and pH 5. When incubated at pH 5, the activity of chitin deacetylase was increased; after 3 h, the activity was 1.5 times of the control. The enzyme was stable at pH 4, after 2 h incubation, the activity was still 80% of the control. The chitinase and chitin deacetylase activities were not influenced by Mg(++) nor Ca(++), Ni(++) and Cu(++) inhibited the chitinase activity, while chitin deacetylase activity was not affected by Cu(++) addition. When 1 mM of EDTA was added, the enzyme activity was reduced 40 to 50%.