Biosynthesis of CGTase by immobilized alkalophilic bacilli and crystallization of beta-cyclodextrin: Effective techniques to investigate cell immobilization and the production of cyclodextrins

Immobilized Cells of Bacillus circulans ATCC 21783 on Palm Curtain for Fermentation in 5 L Fermentation Tanks

Palm curtain was selected as carrier to immobilize Bacillus circulans ATCC 21783 to produce β-cyclodextrin (β-CD). The influence for immobilization to CGTase activity was analyzed to determine the operation stability. 83.5% cyclodextrin glycosyltransferases (CGTase) of the 1st cycle could be produced in the 7th cycle for immobilized cells, while only 28.90% CGTase was produced with free cells. When palm curtain immobilized cells were reused at the 2th cycle, enzyme activities were increased from 5003 to 5132 U/mL, which was mainly due to physical adsorption of cells on palm curtain with special concave surface structure. Furthermore, conditions for expanded culture of immobilized cells in a 5 L fermentation tank were optimized through specific rotation speed procedure (from 350 r/min to 450 r/min with step size of 50 r/min) and fixed ventilation capacity (4.5 L/min), relations between biomass, enzyme activity, pH, and oxygen dissolution was investigated, and the fermentation periods under the two conditions were both 4 h shorter. Compared with free cell, immobilized cell was more stable, effective, and had better application potential in industries.

Heterotrophic culture of Chlorella pyrenoidosa using sucrose as the sole carbon source by co-culture with immobilized yeast

Glucose is normally used as the carbon source for heterotrophic cultivation of algal cells, whereas sucrose is difficult to be heterotrophicly utilized by them. In this study, a new co-culture system was developed through mixed culture of Chlorella pyrenoidosa with immobilized Saccharomyces cerevisiae in the dark to effectively obtain pure algal suspension using sucrose as only carbon source. In this system, a pure algal suspension with a concentration of 2.08g/L was obtained. The lipid content reached 29%, which was higher than that obtained in glucose contained system. In addition, the immobilized yeast beads were repeatedly used for at least three times. Through immobilization, the choice for the yeast strains that are able to hydrolyze sucrose was not limited by its product and pure algal suspension was efficiently obtained. This strategy may effectively decrease the cost of carbon source in the heterotrophic cultivation of microalgae.

Integral Use of Amaranth Starch to Obtain Cyclodextrin Glycosyltransferase, by Bacillus megaterium, to Produce β-Cyclodextrin

Cyclodextrin glycosyltransferase (CGTase) is an enzyme that produces cyclodextrins (CDs) from starch and related carbohydrates, producing a mixture of α-, β-, and γ-CDs in different amounts. CGTase production, mainly by Bacillus sp., depends on fermentation conditions such as pH, temperature, concentration of nutrients, carbon and nitrogen sources, among others. Bacillus megaterium CGTase produces those three types of CDs, however, β-CD should prevail. Although, waxy corn starch (CS) is used industrially to obtain CGTase and CDs because of its high amylopectin content, alternative sources such as amaranth starch (AS) could be used to accomplish those purposes. AS has high susceptibility to the amylolytic activity of CGTase because of its 80% amylopectin content. Therefore, the aim of this work was evaluate the AS as carbon source for CGTase production by B. megaterium in a submerged fermentation. Afterwards, the CGTase was purified partially and its activity to synthesize α-, β-, and γ-CDs was evaluated using 1% AS as substrate. B. megaterium produced a 66 kDa CGTase (Topt = 50°C; pHopt = 8.0), from the early exponential growth phase which lasted 36 h. The maximum CGTase specific activity (106.62 ± 8.33 U/mg protein) was obtained after 36 h of culture. CGTase obtained with a Km = 0.152 mM and a Vmax = 13.4 μM/min yielded 40.47% total CDs using AS which was roughly twice as much as that of corn starch (CS; 24.48%). High costs to produce CDs in the pharmaceutical and food industries might be reduced by using AS because of its higher α-, β- and γ-CDs production (12.81, 17.94, and 9.92%, respectively) in a shorter time than that needed for CS.

Ultrafiltration system for cyclodextrin production in repetitive batches by CGTase from Bacillus firmus strain 37

This study aimed to improve the yield of cyclodextrins (CDs) production in repetitive batches. An innovative ultrafiltration system was used to remove the inhibitory products that accumulated in the medium and to recover the enzyme. The assays were performed with the CGTase from Bacillus firmus strain 37 in purified, semi-purified, and crude extract forms. Maltodextrin (10% w/v) and corn starch (5% w/v) were used as substrates. After eight repetitive 24-h batches, the yield of β-CD obtained with the purified enzyme and the corn starch substrate was 0.54 mmol/L/h, which was 36% greater than that observed with the 10% maltodextrin substrate. The crude CGTase extract with the corn starch substrate showed a productivity of 0.38 mmol/L/h, which was 29% lower than using the purified enzyme and the corn starch substrate but 7% higher than using the purified enzyme and the maltodextrin substrate. The crude extract, assayed with the corn starch substrate in the presence of 10% ethanol reached 0.43 mmol/L/h productivity, which was 12% higher compared to the assay without ethanol. The semi-purified enzyme was assayed with the corn starch substrate in the presence of 10% ethanol for eight batches lasting 12 h and an excellent selectivity for the β-CD was obtained, reaching a mean percentage of 96.0%. Therefore, this ultrafiltration system enabled several batches of CD production, with efficient removal of products inhibitory to the CGTase and recovery of the enzyme. The possibility of industrial application of this system is promising.

Cyclodextrin glycosyltransferase production by free cells of Bacillus circulans DF 9R in batch fermentation and by immobilized cells in a semi-continuous process

Cyclodextrin glycosyltransferase (CGTase) catalyzes starch conversion into cyclic or linear oligosaccharides, important industrial products for the complexation of non-polar substances. In this work, conditions to increase CGTase production from Bacillus circulans strain DF 9R were optimized by two systems. On one hand, free cells were grown in batch fermentation experiments to optimize aeration and pH. The highest activity (1.47 ± 0.21 U ml(-1)) was achieved after 48 h of growth, aeration of 1.5 vvm and pH regulated to 7.6. On the other hand, bacterial cells were immobilized on loofa and synthetic sponge, and used for CGTase production in a semi-continuous process. An initial biomass of 30 mg of lyophilized cells and an immobilization time of 24 h with loofa or synthetic sponge were enough to achieve increased production of CGTase: 0.91 ± 0.10 and 0.95 ± 0.11 U ml(-1), respectively. Sponges with immobilized bacteria were reused in 12 successive cycles. Besides, in our conditions, CGTase was not adsorbed onto the supports used for immobilization, which ensured the total recovery of the enzyme from the culture medium. The two CGTase production processes studied showed similar productivity and could be potentially scaled up.