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Bacillus circulans was able to produce extracellular levansucrase using sucrose as carbon source optimally at 35°C. The enzymic synthesis of levan and fructo-oligosaccharides was studied using a 50% ethanol fraction of crude extract. The molecular weight of the synthesized levan was markedly affected by sucrose concentration, the molecular weight of levan decreased with increased sucrose concentration up to 32% whereby fructooligosaccharides were isolated. Temperature and the reaction time clearly affected the conversion of fructose to levan with molecular weight values ranging from 10 to 38 kDa. Identification of levan indicated that fructose was the building unit of the levan obtained. Thermal and pH stabilities of B. circulans levansucrase could be improved by enzyme glycosylation using sodium metaperiodate treatment. Chemical modification provides additional points of attachment of the enzyme to the support which offered the modified enzyme greater stabilization than did the free enzyme. The modified enzyme exhibited thermal tolerance up to 50°C, where it retained 88.25% of its activity, while the free enzyme only retained 64.55% of its original activity. The half-life significantly increased from 130 min for the free enzyme to 347 min for the modified enzyme at 50°C, however, it increased from 103 min for the free enzyme to 210 min for the modified enzyme at 60°C. Other properties i.e., the response to some metal ions as well as the ability to convert higher substrate levels and tolerance to an extension of the reaction periods were also improved upon modification. Obviously, the results obtained outlined the conditions leading to the formation of important high or low molecular weight or levan and fructo-oligosaccharides suitable for different industrial applications.

Statistically-based experimental designs were used to optimize the production of cyclodextrin glucosyltransferase (CGTase) from a local isolate of Bacillus megaterium using shack culture fermentation. Seven cultural conditions were examined for enzyme production and specifi c activity using Plackett-Burman factorial design. Fermentation time and K 2 HPO 4 level were the crucial for factors improving enzyme production process. The steepest ascent design was adopted-based on the results recorded with Plackett-Burman design. Maximal enzyme estimates (activity 56.1 U/ml, and specifi c activity 62.7 U/mg protein) were achieved. A verifi cation experiment was carried out to examine model validation of this optimization.

Aims:  The objective of this study was to enhance the production of cyclodextrin glucanotransferase (CGTase) produced by a local isolate Bacillus cereus NRC7. Methods and Results:  In batch culture, maximal CGTase activity (69·0 U ml−1) was reached after 24‐h incubation period. In continuous production of CGTase by the free cells of B. cereus NRC7, maximal reactor productivity (11·76 KU l−1 h−1), with enzyme concentration of 49·0 U ml−1 and specific productivity of 904·6 U per g wet cells per h, was attained at dilution rate of 0·24 h−1, over a period of 640 h. Bacillus cereus NRC7 cells were immobilized on chitosan. The immobilization conditions with respect to matrix concentration and maximal cell loading were optimized for maximal CGTase production. In repeated batch operation, the activity of the immobilized cells was stable during ten cycles and the activity remained between 51 and 55 U ml−1. In packed‐bed reactor, the immobilized cells showed maximal productivity (27·18 KU l−1 h−1) with enzyme concentration of 54·63 U ml−1 and specific productivity of 151·89 U per g wet cells per h at dilution rate of 0·5 h−1. The half‐life of the immobilized cells was higher than 20 days. Conclusions:  Continuous fermentation by the immobilized cells in packed‐bed reactor is an appropriate potential technique for B. cereus NRC7 CGTase production that gave maximum productivity (27·18 KU l−1 h−1), which was 9·47‐, 2·31‐, 12·24‐ and 12·94‐fold higher than the free cells in batch, free cells in continuous, immobilized cells in batch and repeated batch cultures, respectively. Significance and Impact of the Study:  This is the first study that evaluates CGTase productivity, in different fermentation modes, in terms of specific productivity (U per gram cells per h). In continuous fermentation by immobilized cells, maximal levels of CGTase productivity are higher than the previously reported values.